HVAC Glossary - NB Handy HR



HVAC Glossary

AC - Alternating current (wall plug).

ACR tubing - Copper tubing made especially for refrigeration and HVAC work. It is especially clean and is usually charged with dry nitrogen. The ends are sealed to prevent contamination.

ASHRAE - American Society of Heating, Refrigeration and Air Conditioning Engineers.

ASTM - Abbreviation for American Society for Testing and Materials.

AWG - American Wire Gauge.

Abrasive - Substance used to wear away material (e.g., sandpaper).

Accumulator - A series of fixed and movable rolls which act as a reservoir of strip in a continuous coating or metal processing line. Usually accumulators are found at both the beginning and end of a line. Their purpose is to provide enough strip to avoid the necessity of stopping the process section of the line when attaching a new coil at the entrance or removing a coil at the exit.

Acme Lock - A sheet metal lock made by turning the edges of adjoining sheets 180 degrees in opposite directions, hooking them together and locking them with the aid of a grooving tool.

Acrylics - (Paint) A thin film coating of acrylic resins.

Acute - Angle less than 90 degrees.

Age Hardening - The tendency of a material to lose formability with the passage of time.

Aging - A term applied to changes in physical and mechanical properties of low carbon steel that occur with the passage of time.

Air (Standard) - Dry air under a pressure of 14.7 pounds per square inch and with a temperature of 70 degrees Fahrenheit.

Air Cleaner - A device designed for the purpose of removing airborne impurities such as dust, gases, vapors, fumes, and smoke. Air Cleaners include air washers, electrostatic precipitators, and mechanically operated filtering devices which put a barrier or filter in the air stream to remove unwanted things. Panel type air filters are not considered in this category.

Air Conditioning - The process of treating air so as to control simultaneously its temperature, humidity, cleanliness, and distribution to meet the requirements of the conditioned space.

Air Filters - Nonmechanical air-cleaning devices. In general, air filters are panel type frames filled with treated media. Such filters are either disposable or cleanable.

Air Throw - The distance an air stream travels from an outlet to a position where its motion has been reduced to a velocity of 50 feet per minute.

Alloy - A substance that is a mixture of two or more metals.

Aluminizing - Applying a coating of aluminum or aluminum silicon to steel by the hot dipping process.

Ambient Temperature - The temperature of air before it has been heated or cooled.

American Society For Testing and Materials (ASTM) - Founded in 1898, ASTM International is a not-for-profit organization that provides a global forum for the development and publication of voluntary consensus standards for materials, products, systems, and services. Of specific interest to NBH are standards for copper, corrosion and wear, fasteners, metallic coatings, roofing, rubber and steel. ()

Annealing - The heating and controlled cooling of a material for the purpose of removing stresses, making it softer, refining its structure, or changing its ductility, toughness, or other properties.

Annual Fuel Utilization Efficiency (AFUE) - HVAC industry standard for defining furnace efficiency.

Anodizing - (Aluminum Anodic Oxide Coating) A process of coating aluminum by electrolytic oxidation resulting in a thin film of aluminum oxide of extreme hardness. A wide variety of dye-colored coating is possible by adding pigments during the process.

Anvil - An iron or steel block on which metal objects are hammered into shape.

Applicator Roll - The roll on a roller coater which applies the paint, conversion coating or other liquids to a moving strip of metal, sometimes called the transfer roll.

Arc - A line segment formed by a portion of a circle.

Architect - A licensed and registered professional who designs and supervises the construction of buildings.

Asbestos - A fibrous mineral once used due to its fire-resistive properties. It is a carcinogen and is no longer used. Retrofit work involving asbestos is extremely hazardous and expensive due to federally mandated asbestos abatement procedures.

Auger - A tool with a spiral cutting edge for boring holes in wood and other materials.

Auxiliary Drawings - Drawings that are supplementary to the working drawings. Examples: Electrical Plan, HVAC Plan, Plumbing Plan, Door/Window Schedules, Foundation and Framing Plans.

Back Coat - A coating applied to the back side of the strip. This coating is controlled for consistent color, gloss, and applied dry film thickness. It is both decorative and functional in use. Not to be confused with a wash coat.

B101 (ASTMB101) - Standard material specification for lead-coated copper sheet and strip for building construction. (See for a summary of the standard)

B370 (ASTMB370) - Standard material specification for copper sheet and strip for building construction. (See for a summary of the standard)

Ball peen hammer - A hammer with a flat face used for striking and a rounded front section.

Band Mark - An indentation caused by the packaging band resulting from external pressure on cut lengths or coils of metal. Marking may occur in handling, transit, and storage.

Bar Folder - The first sheet metal bending machine. Currently used primarily for bending drive cleats or making hems on metal with a raw edge.

Bay - A compartment set off from other compartments making up a given structure.

Bell faced hammer - A claw hammer with a slightly rounded, or convex, face.

Bending - A mechanical forming process with the metal at room temperature or at elevated temperatures primarily used to produce angled pieces of sheet metal or curved sections from straight lengths of tube, rod, or extruded shapes. Accomplished with the aid of brakes, rollers, bending shoes, and mandrels.

Bevel cutting - Cutting at an angle other that a right angle; sloped.

Beveled - Cut at an inclination that forms an angle other than a right angle.

Bimetallic Element - An element made of two metals having different coefficients of thermal expansions.

Black Iron Pipe - Carbon steel pipe that gets its black coloring from the carbon in the steel.

Blank - A flat piece of sheet steel produced in blanking dies or by shearing for an identified part. The blank is usually subjected to further press operations

Blanket Insulation - Fiber glass insulation in roll form used with a vapor retarder membrane laminated to the inside face.

Blanking - A punching operation where the slug is kept as the desired part.

Blind Rivet - A rivet applied from one side incorporating a stem which pulls against material on the blind side and 'pops' off when the rivet is fully formed.

Blueprint - A photographic reproduction, as of architectural plans, shown as white lines on a blue background (also referred to as "working drawings" and "construction drawings").

Boiler - A closed vessel in which water is heated or steam is generated.

Bore - Inside diameter of a cylinder.

Brake - Any of several types of machines for bending sheet metal. One of the most basic pieces of sheet metal fabrication equipment (v. the action of bending sheet metal).

Brake Forming - A mechanical bending operation usually performed on sheet, strip, and plate metal.

Brazing - An intermediate temperature joining process using a non-ferrous filler metal with a melting point above 800 degrees Fahrenheit, but generally lower than that of the base metals. The filler metal is drawn between the closely fitted surfaces of the joint by capillary action.

Brinnell Hardness Test - A test which measures the hardness of bare metal, conducted by forcing a ball of standard diameter into the surface under standard pressure and judging hardness by the amount of material displaced.

British Thermal Unit (BTU) - The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.

Buckles - A series of waves in sheets which are ordinarily transverse to the direction of rolling. In formed panels, "excess metal" in the form of wrinkles, kinks, or folds.

Building Code - Any system of principles or rules set to control, design, or construct buildings or materials. Building Codes are generally set by national standards and enforced by local code officials. Selection of which codes to apply and deviations within the specific codes are local or state decisions.

Burnishing - A change of gloss induced by friction between two surfaces.

Bushing - Pipe fitting with male threads on the outside and female threads on the inside. Most often used to connect the male end of a pipe to a fitting of a larger size.

Button, Clip Punched - When two or more pieces of metal are to be joined by slipping together, the union can be made tight by the use of a tool that forces a deep indentation into all pieces of metal at one time. These indentations are generally spaced about 18 inches apart.

CDA - Copper Development Association.

CFM - Cubic Feet per Minute, a measurement of air movement.

C.M.U. - Concrete Masonry Unit; concrete block or cinderblock.

C.S.A - Canadian Standards Association.

CSI - Construction Specifications Institute. This organization developed the Uniform Construction Index which provides a uniform system for arranging specifications and product information pertaining to a construction project ("Division 7," etc.).

C-factor - A measurement of resistance to heat flow. The C-factor is measured in terms of the total performance of the insulating material. It is the reciprocal of the R-value (when expressed in inches). A product with an R-value of 5.14 has a C-factor of 0.195 (1 divided by 5.14). The lower the C-factor, the more the insulating value. See also R-value, K-factor and U-factor.

Camber - The deviation of a side edge of metal sheet from a straight line. The measurement is taken on the concave side using a straight edge. Long lengths of unsupported metal having a large amount of camber tend to deviate from the horizontal or slope to one side.

Cap Strip - A strip of metal which has had its two edges turned 180 degrees inward and on the same side of the metal strip. (Used to form a drive seam.)

Capacitor - A device used to introduce capacitance into an electric circuit. Used in the starting circuit of some electric motors.

Cast - To form by pouring or pressing into a mold. Weaker than dropped-forged.

Casting - Forming an article by solidification of molten metal in a mold.

Caulking - Any of a wide range of bituminous, rubber, plastic, or other materials suitable for filling seams or cracks to make them tight against air and/or water infiltration.

Center Buckle - An "out of flat" condition caused by stretching of the metal so that the center of the sheet is longer than the edges.

Chalking - A process by which finishes develop a loose powdery surface resulting from decomposition of the binder, principally through the action of ultraviolet rays.

Change of State - Changing from a solid to a liquid or from a liquid to a vapor. Also the reverse of this procedure.

Chatter - In metal processing, either 1) a transverse series of marks or lines on the metal surface caused by vibration or eccentric rolls on a tandem or temper mill or 2) a transverse series of marks or lines occurring in the coating caused by vibration or eccentric coater rolls.

Check Valve - A one-way value in the discharge line of a refrigerant circuit or a water line which prevents the liquid in the line from draining back "upstream."

Chimney - A vertical shaft enclosing one or more flues for conveying flue gases to the outside atmosphere. (a) Factory-Built Chimney. AUL listed. (b) Masonry Chimney. A chimney of solid masonry units, bricks, stones, listed masonry units or reinforced concrete lined with suitable flue liners.

Chuck - A clamping device which holds the attachment to be turned; for example, the chuck of the drill holds the drill bit.

Chuck key - Small T-shaped steel tool used to open and close the chuck on power drills.

Circumference Rule - A 48" long steel scaled rule used in sheet metal pattern layout. One edge has standard measurement scales, the other has conversions that assist in determining circumferences of a circle, based on a given diameter.

Cleats - Used to fasten sheet metal to other materials. Usually formed from 2 inch wide strips that are folded 180 degrees at one end for fastening under a 180 degree fold along the edge of the sheet being anchored. The cleat is usually nailed to other materials and the remaining metal bent back over the nail heads.

Coater or Roll Coater - An apparatus that applies paint, conversion coating or other liquids to a flat metal strip. The coater consists of rolls for supporting a strip through the apparatus and for the pick up, metering and deposition of material onto a moving strip of metal.

Coil - 1. In HVAC, a cooling or heating element made up of pipe or tubing. 2. In steel and other sheet metals - sheet metal that has been wound. A slab, once rolled in a hot strip mill, is more than 1/4 mile long. Coils are the most efficient way to store and transport sheet metal.

Coil Breaks - Creases or ridges appearing in sheets as parallel lines transverse to the direction of rolling and generally extending across the width of the sheet.

Coil Set - A tendency of a length of metal cut from coil to maintain the curved shape of the coil diameter from which it was cut.

Coil Weld - A joint between two lengths of metal within a coil - not generally visible in the cold reduced product.

Cold Rolled Finish - The finish obtained by cold rolling of plain pickled strip with a lubricant giving a relatively smooth appearance. In the case of sheet or strip, cold rolling may be done without any lubricant so the finish then is similar to that described under "Dry Rolled Finish."

Cold Rolling - The process of passing metal between rolls under pressure to reduce its cross section (width or height) while the metal temperature is below its softening point.

Combustible - Capable of catching fire and burning.

Combustible Material - Pertaining to materials adjacent to or in contact with heat producing appliances, vent connectors, gas vents and chimneys. Materials made of wood, compressed paper, plant fibers, or other materials that will ignite and burn. Such material shall be considered combustible even though flame proofed, flame-retardant treated, or plastered.

Combustion - Rapid oxidation of fuel gases accompanied by the production of heat or heat and light. Complete combustion of a fuel is possible only in the presence of an adequate supply of oxygen.

Combustion Air - Air supplied to an appliance specifically for the combustion of fuel.

Common Vent - The portion of a vent system into which the vent gases from two or more appliances flow.

Companion Angle Joints - This transverse joint is formed when angle frames are bolted, riveted, or welded to duct ends and are then bolted together with gaskets (or caulked) to prevent air leaking.

Compression Joint - A method of connection in which tightening a threaded nut compresses a compression ring to seal the joint.

Compressor - In a refrigeration system, the mechanical device that converts low pressure, low temperature refrigerant gas to high temperature, high pressure refrigerant gas.

Compressor, Reciprocating - A positive displacement compressor utilizing a piston that operates first in one direction and then the other.

Compressor, Screw - The spiral flutes of one screw act as a cylindrical pathway for the refrigerant to be moved and compressed by the mating screw as they are rotated at high speed.

Condensate - The moisture that condenses from warm, humid air when exposed to a cooler surface, such as an air conditioner evaporator coil. The energy required to change the humid air to a liquid is referred to as latent energy or latent heat.

Condensate Pump - Small, self-priming pump used near an air conditioner's evaporator to pump excess condensate away from the air handler.

Condensation - The conversion of water vapor or other gas to liquid as the temperature drops or atmospheric pressure rises (see also dew point).

Condenser - A heat exchanger that transfers heat from the refrigerant flowing inside it to the air or water flowing over it.

Condensing Furnace - A furnace that contains a secondary heat exchanger that extracts latent heat by condensing flue gases.

Condensing Unit - The high side of the refrigeration system. In a "split-system" air-conditioning system, it is the "outdoor" unit where the heated refrigerant is cooled and condensed back into liquid form.

Conduction - A means of heat transfer in which heat is moved from one substance to another by means of direct contact.

Construction Drawings - Drawings used in actual construction of a building or part of a building. Also referred to as "Blueprints" and "Working Drawings."

Contactor - A control device consisting of a coil and one or more sets of contacts used as a switching device in high voltage circuits.

Continuity - A continuous current path. The absence of continuity indicates an open circuit.

Contour Lines - Show the rise and fall of land elevation on a site.

Control - Any device used for the regulation of the refrigeration system.

Convection - The transfer of heat by the flow of liquid or gas.

Conversion Coating - A chemical treatment which, by reaction with the metallic surface of the strip, converts this to a non-metallic, non-conductive surface for improved paint adhesion and corrosion resistance after painting.

Convert - To change from one unit or expression to another.

Copper - A ductile, malleable, reddish -brown metal used for roofing and architectural sheet metal applications. Copper is highly resistant to corrosion and weathers to a natural patina color when used in exterior applications.

Corrosion - The electrochemical degradation of metals due to reaction with their environment.

Corrugation - In a metal panel, the formed rib, drawn or rolled into parallel ridges and furrows to provide additional mechanical strength.

Cratering - A surface coating defect related to surface tension. It is characterized by small pock marks or indentures surrounded by a ring of coating material projecting above the general plane of the coating. In severe instances the area in the center of the crater may show the substrate.

Cross Braking - Where additional support is desired in sheet metal ductwork or panels, the sheet may be placed diagonally in a press brake and slightly crimped, then turned and similarly crimped between the two other opposite points, forming a criss-cross in the flat surface of the sheet.

Crown - Increased thickness in the center of a metal sheet or strip as compared with the thickness of the edge.

Curbs, Roof - Raised sections formed at the time the basic roof foundations are installed. They are intended as raised bases for equipment foundations. Curbs should be flashed between the roof and the installed equipment.

Cut List - An information sheet that is derived from shop drawings. Provides a list of materials needed to fabricate a finished component of construction.

Cut Sheet - Schematic or line drawing of an object or design.

DC - Direct current (battery).

Deburring - A method whereby the burr along the slit edge of metal is removed by rolling or filing.

Decibel - An acoustical term used to express the relationship between two sound levels.

Decimal - Part of a number, represented by digits to the right of a decimal point.

Deep Drawing - An extreme condition of drawing sheet metal. The term "deep drawing" is commonly used to describe metal stamping operations which are a combination of drawing and severe stretching.

Defrosting - Removal of accumulated ice.

Dehumidification - The removal of water vapor from air.

Delta - T - The temperature differential between two different materials (air and metal duct) or the temperature differential in air after being heated or cooled.

Denominator - The bottom number of a common fraction, indicates how many equal parts the whole is divided into.

Density - Mass or weight per unit of volume.

Desiccant - Any material that will remove water from a substance.

Detail Drawings - Enlarged views taken from an architectural or engineering drawing. Used to show an area more clearly.

Dew Point - The temperature at which a sample of humid air, cooled from some temperature, becomes saturated and at which water vapor begins to condense to liquid water.

Diameter - The length of a line segment from one edge of a circle to another which passes through the center of a circle. Twice the length of the radius.

Die - The female part of a tool that accepts a formed part or slug produced by a male punch.

Difference - The result of a subtraction problem.

Digit - One of the symbols 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.

Dilution Air - Air which enters a draft hood or draft regulator and mixes with the flue gases.

Dimensions - A definite measurement shown on a drawing as length, width, or height.

Dimple - A defect resulting from foreign matter being mechanically impressed into the sheet surface.

Dings - Accidental impact damage similar in appearance to dimples.

Direct Vent Appliances - Appliances which are constructed and installed so that all air for combustion is derived from the outside atmosphere and all flue gases are discharged to the outside atmosphere

Discharge Line - The high-pressure refrigerant line connecting the compressor to the condenser.

Dispersion - A heterogeneous system in which a finely divided material is distributed in another material. Note: A dispersion is usually the distribution of a finely divided solid in a liquid or a solid; for example, pigments or fillers in coatings. The dispersion of a liquid in another liquid is an emulsion.

Dissimilar Metals - Metals of unlike composition tend to set up a galvanic action that results in rapid deterioration in one or the metals. Dissimilar metals should be insulated from one another by membranes, caulking, or other coatings.

Dividend - In a division problem, the number being divided.

Divisor - In a division problem, the number being divided by.

Double Fold - A straight-edged sheet that has been turned back 180 degrees and again turned another 180 degrees, then flattened.

Double-Insulated - Electric shock protection for power tools utilizing two separate insulating systems, usually consisting of non-conducting housing components and electrically insulated internal components.

Dowel - A pin, usually round, that fits into a corresponding hole to fasten or align two adjacent pieces.

Down draft - A flow of air downward in the stack caused by excessively high air pressures created at the outlet of the chimney or vent cap or by negative pressure at the inlet or the vent system.

Draft - A noticeable current of air that is objectionable to a person (or persons) using a conditioned space.

Draft Hood - A device built into an appliance or made a part of the flue or vent connector from an appliance. It is designed to (1) provide for the ready escape of the flue gases in the event of no draft, back draft, or stoppage beyond the draft hood, (2) prevent a back draft from entering the appliance, and (3) neutralize the effect of stack action of the chimney or gas vent upon the operation of the appliance.

Drawing - The shaping of a flat blank into the desired contour by causing the metal to flow over a draw ring and around a punch. The flow of metal is restrained by sufficient blank holder pressure to prevent buckling.

Drawing Title - Located within the title block of architectural drawings, it identifies the project.

Dropped - forged - Pounded, heated metal. Stronger than cast.

Dry Rolled Finish - The finish obtained by cold rolling on polished rolls without the use of any coolant or metal lubricant on material previously plain pickled, bichromate, or bright dipped.

Duct - Formed section of metal or other materials that distribute conditioned air throughout a building or exhaust air to the outside.

Duct Butter - Duct sealer.

Duct Section - A single piece of duct.

Ductility - The ability of a metal to be deformed plastically by drawing and similar processes without fracturing (see also malleable). The ability to be fashioned into a new form.

Duct work - System for distributing conditioned air within a structure or for exhausting air out of a structure. Usually round or rectangular, duct work is fabricated from metal or fiberglass components.

Durometer Hardness Tester - An instrument for the determination of hardness of elastomers or other compressible rubber-like materials, commonly used for hardness measurement of roll coverings and heavy films of plastic (e.g. plastisols). Test results are displayed as a percentage of scale deflection from 0 to 100 for any given scale employed (most commonly used Shore "A").

ETL - Electrical Testing Laboratories.

Elastic Limit - Maximum stress that a material will stand before permanent deformation occurs.

Elastomer - Any of several elastic substances that, at room temperature, resemble and display the qualities of rubber.

Electro - magnetic - Magnetism developed by the application of a current of electricity. Typically, a soft iron core surrounded by a coil of wire that temporarily becomes a magnet when an electric current flows through the wire.

Electrostatic - Capable of generating a static electrical charge, the state of an electrical charge having been applied to materials so that particles are attracted. In HVAC, filters which generate a static electrical charge to enhance particle adhesion.

Elevation Drawings - The side view of a building or object. Shows height and width but not depth.

Elevation - Height above sea-level (or the defined surface), usually expressed in feet. Elevation (ELEV) is given at each corner of the site.

Elongation - Increase in length which occurs before materials fracture when subjected to stress. This is usually expressed as a percentage of the original length and is a measure of ductility.

Embossing - The process of decorating or covering with design by depressing the surface using a pattern roll.

Enamel - 1. A type of paint consisting of an intimate dispersion of pigments in a resin vehicle. 2. Porcelain enamel.

Energy Efficiency Ratio - The ratio of the rated cooling capacity in BTU's per hour divided by the amount of electrical power in watts at any given set of conditions.

Engineer - One who applies scientific principles for practical purposes in the design, construction, and application of efficient and economical structures, equipment, and systems.

Equipment Screen - False wall used to conceal HVAC/mechanical equipment housed on a flat roof.

Equivalent Fractions - Fractions having different numerators and denominators but equal value such as 1/2 and 2/4.

Evaporator -A heat exchanger that transfers heat from the air flowing over it to the cooler refrigerant flowing through it. In a "split-system" air conditioning system, it is the "indoor" unit.

Exhaust System - An exhaust air system designed to evacuate air from selected areas and to discharge it to the atmosphere. Such exhausted air may or may not be treated prior to being discharged.

Expansion device - Also known as the liquid metering device or metering device. Provides a pressure drop that converts the high temperatures, high pressure liquid refrigerant from the condenser into the low temperature, low pressure liquid refrigerant entering the evaporator.

Extension ladder - Two straight ladders assembled such that the overall length of the combination can be adjusted.

Extractors - A set of curved blades formed into a unit that can be adjusted to direct air flow into a branch duct or supply outlet to provide positive control of air volume and to smooth out air turbulence.

Extrusion - The process of shaping heated metal into a chosen continuous form by forcing it from a closed container through a die of appropriate shape.

Exude - The migration of coating components toward an interface, usually the outer coating surface, during curing, storage, or use.

Fan - Assisted Combustion - The use of a fan (blower) to support the burning of gas and the removal of the products of combustion from the appliance. The fan may be upstream or downstream of the combustion chamber.

Fastener - A device used to attach or secure materials of various types one to another thing, e.g., bolt, nail, screw, etc.

Fatigue - The phenomenon in sheet metal of leading to fracture under repeated fluctuating stress. Fatigue fractures are progressive, beginning as minute cracks, and grow under the action of fluctuating stress.

Ferromagnetic - Of or characteristic of substances, as iron, nickel, cobalt, and various alloys, that have magnetic properties.

Ferrous - Related to iron (derived from the Latin "ferrum"). Ferrous alloys are iron base alloys.

Fire Dampers - A damper installed in ducts or walls to retard the spread of fire. Such dampers are fabricated to operate at predetermined temperatures and to have overlapping blade edges along the top and bottom of the frame and where contact is made with other blades.

Firestop - A blockage place in a hollow wall or opening in any other part of a building structure to halt upward progress of fire through the wall or opening.

Fish - Eye - An elongated crater (see Cratering).

Flare Fitting - A fitting in which the end of each tube to be joined is flared outward using a special tool. The flare tube ends mate with the threaded flare fitting and are secured to the fitting with flare nuts.

Flash Gas - The gas resulting from the instantaneous evaporation of the refrigerant as it enters a low pressure area.

Flat - Lock Seams - Made by turning 180 degrees the edges of adjoining sheets in opposite directions, hooking them together and locking them with the aid of a grooving tool.

Floor Plan - A building drawing indicating a plan view of a horizontal section at some distance above the floor, usually midway between the floor and ceiling.

Flue - 1. The general term for the passageways in a furnace and chimney through which combustion products pass to the outside atmosphere. 2. Appliance Flue - The flue passageways within a furnace. 3. Chimney Flue - The vertical conduit for conveying combustion products delivered to it by a vent connector to the outside atmosphere.

Flue Gases - Products of combustion plus excess air in appliance flues or heat exchanges (before the draft hood).

Flue Outlet - The opening provided in an appliance for the escape of flue gases.

Fluting - A series of sharp parallel kinks or creases occurring in the arc when sheet steel is roll formed into a cylindrical shape.

Flux - A chemical substance that prevents oxides from forming on the surface of metals as they are heated for soldering, brazing, or welding.

Foil - Metal in any width not more than about 0.005" thick.

Forging - A forming process in which the metal is shaped as desired by repeated blows.

Foring - A method of forming parts by pressing a heated slug or blank cut from wrought material into a closed impression die.

Fraction - A number represented by a numerator and denominator, such as 1/2.

Ft. - Abbreviation for "foot" or "feet."

G-90 - Galvanized steel coating designation. The G-90 designation indicates that a given sheet or coil would have .90 ounces of zinc coating per square foot total for both sides of the product.

G-60 - Galvanized steel coating designation. The G-60 designation indicates that a given sheet or coil would have .60 ounces of zinc coating per square foot total for both sides of the product.

G-40 - Galvanized steel coating designation. The G-40 designation indicates that a given sheet or coil would have .40 ounces of zinc coating per square foot total for both sides of the product.

G.P.H. - Gallons per hour.

Gage, Gauge - A designation of metal thickness.

Galvalume - Black carbon sheet steel having a hot dipped coating of corrosion resistant aluminum-zinc alloy.

Galvanized - Black carbon sheet steel having a hot dipped or electro deposited coating of zinc alloy.

Galvanizing - Applying a coating of zinc to steel; application may be hot-dipping or electro-deposition.

Galvannealed Coating - Galvannealed sheets are hot dipped zinc coated sheets which have been processed to produce a zinc-iron alloy coating. This product does not have a spangle and is suitable for painting after cleaning. The alloy produced lacks ductility, and powdering of the coating can occur during forming.

Gas Vents - Factory-built vent piping and vent fittings listed by a nationally recognized testing agency that are assembled and used in accordance with the terms of their listings for conveying flue gases to the outside atmosphere.

(a) Type B Vent: A gas vent for venting gas appliances with draft hoods and other gas appliances listed for use with Type B Gas Vents.

(b) Type BW Vent: A gas vent for venting listed gas-fired vented wall furnaces.

(c) Type L Vent System: A vent system intended for use with appliances having a flue gas temperature higher than can be accommodated by a Type B gas vent. Must only be used with appliances listed for safe operation with Type L.

Government Lock - A transverse joint formed by placing a right angle flange with and "S" type slip arrangement over the end of one duct section and fastening by button punching. A second duct section with a short 90-degree right angle flange is inserted into the first flange arrangement, then the higher flange is turned over the inserted flange to form a tight lock. (Also known as a Pocket Lock or a Box Lock.)

Grille - A covering for the termination of an HVAC duct, does not have a damper. Has bars or vanes which help direct the airflow in a predetermined pattern.

Ground Fault Protection - An electrical safety device that cuts power as soon as it senses any imbalance between incoming and outgoing current.

Gutters - The troughs used to carry water along the horizontal plane of a roof.

HACR Circuit Breaker - A circuit breaker with a built-in trip delay used specifically in HVAC circuits because of the power surge that occurs with compressor start-up.

Hand brake - A brake which is operated by hand, with electrical, mechanical or hydraulic compressor start-up, used to form sheet metal.

Hangers - Supports, generally of metal, used to hold duct work and piping in place. They may be attached to beams, etc., or may be in the form of brackets and attached to walls. Spacing of hangers varies with the application.

Hazard Communication Standard - The Occupational Safety and Health Administration standard which requires all contractors to educate employees about hazardous chemicals and the methods to work safely in their presence.

Hazardous Materials - Materials (e.g., chemicals) which must be transported, stored, applied, handled, and identified in accordance with Federal, State, or Local regulations. Must be accompanied by Material Safety Data Sheets (MSDS).

Heat - A form of energy. It causes molecules to be in motion and raises the temperature of a substance. Other forms of energy like electricity, light, and magnetism deteriorate into heat.

Heat Content - The amount of heat energy contained in a substance. Measured in BTU's.

Heat Exchanger - A chamber in the furnace that transfers the heat of combustion to the moving air without direct contact between the combustion gases and room air. Also a device to transfer heat between two physically separate fluids (gas or liquid).

Heat Pump - An air conditioning unit that has been designed to reverse the refrigerant cycle when necessary. This allows the unit to provide cooling to a structure in the summer and heating in the winter.

Heat Transfer - The transfer of heat from a warmer substance to a cooler substance.

Hem or Crushed Fold - A straight-edged sheet that has been turned 180 degrees and the fold flattened.

High Side - High pressure side of a refrigeration system.

Hot Dip - In steel mill practice, a process whereby ferrous alloy base metals are dipped into molten metal, usually zinc, aluminum, tin or terne for the purpose of fixing a rust resistant coating.

Hot Rolled - Hot rolled sheets are those in which slabs are reduced to required thickness at temperatures at which scale is formed and, therefore, carry hot mill oxide.

Hot Rolled Finish - The finish obtained by rolling metal while hot resulting in a dark, oxidized, and relatively rough surface.

Hot Rolled, Pickled - The hot rolled product which has been pickled to remove the hotmill oxide.

Hot Rolling - The process of passing a metal slab between rolls under pressure to reduce its cross section (height or width) while the metal temperature is above softening point.

Hot Surface Igniter - A ceramic device that glows when an electrical current flows through it. Used to ignite gas in a gas furnace.

Humidistat - A control that is responsible for changes in the relative humidity of air.

HVAC - Heating, Ventilation, Air Conditioning.

Hydraulic tools - Tools powered by fluid pressure. Hand pumps or electric pumps are used to produce hydraulic pressure.

Hydrostatic Test - A test designed to assure tight joints in a piping system.

ICBO - International Conference of Building Officials. Maintain the Uniform Building code.

Impact Resistance - Capability to withstand mechanical or physical abuse under severe service conditions. Resistance to blows, bumps, and shocks incident to use.

Impact Test - A test using a steel ball of established weight and diameter dropped from varying heights to determine impact values. Commonly used to determine adhesion and flexibility of a coating.

Impact Valves - Resistance to shock and ability to distribute localized stress as measured by an impact test usually expressed in inch-pounds.

Improper Fraction - A fraction where the numerator is larger than the denominator.

In. - Abbreviation for "inch."

Inclusions - In metal processing 1) particles of non-metallic material, usually oxides, sulphides, silicates, and such which are mechanically entrapped within solid metal sheet or 2) particles or agglomerates which are mechanically entrapped within a finish.

Induced - Draft Furnace - A furnace in which a motor-driven fan draws air from the surrounding area or from outdoors to support combustion.

Infiltration - Air that enters a building through doors, windows, and cracks in the construction.

Insulation - A substance that retards the flow of heat.

Insulation Pins - A spindle-shaped metal or other material with serrations near the pointed end for attaching washer type insulation retainers to metal or other surfaces.

Invert - To reverse the order or position of numbers; in common fractions, to turn them upside down, such as 2/3 to 3/2.

K - factor - A measurement of resistance to heat flow. The K-factor has a constant value for one inch of a given insulating material. It is the reciprocal of the R-value (when expressed in inches). A product with an R-value of 4.17/inch has a K-factor of 0.24 (1 divided by 4.17). The lower the K-factor, the more insulating value. See also R-value, C-factor, and U-factor.

Kerf - Cut or channel made by a saw.

Killed Steel - Steel deoxidized with certain deoxidizing elements, such as aluminum, silicon, etc. The term "killed" is used because such additions cause the steel to lie quietly in the molds during solidification.

Labeled - Equipment or materials affixed with a recognized symbol, acceptable to a local inspector, building department, etc., that the equipment/material is in compliance with recognized safety and performance standards.

Laminate - A composite of two or more dissimilar materials.

Lanyard - A short section of rope used to attach a worker's safety harness to a strong anchor point located above the work area.

Latent Heat of Condensation - The heat given up or removed from a gas in changing back to a liquid state (steam to water).

Latent Heat of Fusion - The heat gained or lost in changing to or from a solid (ice to water or water to ice).

Latent Heat of Vaporization - The heat gained in changing from a liquid to a gas (water to steam).

Legend - Explains or defines a symbol or special mark placed on a drawing.

Level - Perfectly horizontal.

Leveling - 1. The phenomenon by which paint flows out to minimize surface irregularities and approaches a smooth surface. 2. Flattening metal sheet.

Lift - The vertical distance a condensate pump can pump liquid at its stated capacity (G.P.H.).

Lined Ductwork - Duct sections that have been fabricated with inside acoustical insulation to reduce noise transmission within the duct system or as thermal lining where ductwork is exposed to weather.

Liquid Line - The high-pressure liquid line running from the condenser to the refrigerant expansion device.

Listed - Equipment or materials included in a list, published by a nationally recognized testing laboratory that conducts periodic inspections of the production of listed equipment or materials. The listing states either that the equipment or materials meet nationally recognized standards or has been tested and found suitable for use in a specific manner.

Lockout/Tagout - An established, formal procedure for deactivating equipment and systems making them safe for work.

Longitudinal Joint - A seam running the length of a fabricated item.

Make - up Air - Air introduced into an air distribution system to replace air removed through an exhaust system. Air so introduced may have been given some treatment to adjust its temperature and cleanliness to that of the recirculated air.

Malleable - Capable of being shaped or formed by hammering or stamping (see also ductile).

Mallet - A short-handled hammer, usually with a cylindrical head of wood.

Manometer - Device used to measure small pressures such as the static pressure of duct systems.

Masonry - Building material made of stone, brick, concrete block, etc.

Material Safety Data Sheet - A document accompanying any material which contains the identity of the substance, exposure limits, its physical and chemical characteristics, the nature of the hazard it presents, precautions for safe handling and use, and specific control measures.

Matte Surface - A surface with low luster or gloss. A uniform surface lacking gloss.

Mechanical Properties - The properties of a material that reveal its elastic and plastic behavior when force is applied; for example, yield strength, ultimate strength, elongation, hardness, etc.

Mechanical refrigeration - The use of machinery to provide cooling.

Mesh - The square opening of a sieve.

Metallizing - Coating of material with a deposit of metal.

Metric Ruler - Instrument that measures in Metric units (millimeters, centimeters, meters).

MicroFlex - Fully annealed, dead soft, chrome-nickel stainless steel. Usually type 304 AISI specification range. The material can be easily formed with conventional hand tools and can be used for roofing or other architectural sheet metal applications. MicroFlex is highly resistant to corrosion.

Micrometer - An instrument used for mechanically measuring the dry film thickness of finishes or the thickness of metal.

Mil - A unit used in measuring thickness, being 0.001 inch. (British equivalent: Thou. -- Metric equivalent: 0.0254).

Mild Steel - A low carbon steel, approximately 50,000 PSI yield strength.

Minimized Spangle - Minimized spangle galvanized sheet has very small spangles which are obtained by treating the galvanized sheet during the solidification of the zinc to restrict the normal zinc spangle formation.

Mixed Numbers - Combination of whole numbers with fractions or decimals.

NAIMA - North American Insulation Manufacturer's Association.

NEC - National Electric Code.

N.F.P.A. - National Fire Protection Association.

N.R.C. - Noise Reduction Coefficient.

N.S.F - National Sanitation Foundation.

Natural - Draft Furnace - A furnace in which the natural flow of air from around the furnace provides the air to support combustion.

Negative Numbers - Numbers less than zero.

Nipple - Short length of pipe, usually less than 12 inches, with male threads on both ends; used to join fittings.

Nominal - According to generally accepted standards of quality or approximation of size (esp "nominal dimensions").

Non-Ferrous Metals - Metal or alloys that are free of iron.

North Arrow - Positions the architectural drawings toward North (compass orientation).

Numerator - The top number of a fraction, representing the number being divided.

OEM - Original Equipment Manufacturer.

OSHA - The Occupational Safety and Health Administration; an agency of the U.S. Department of Labor.

OSHA Recordable - An injury, accident, or illness which must be reported under the provisions of the Occupational Safety and Health Act of 1970 by recording it on the employer's injury and illness log.

Obtuse - An angle greater than 90 degrees and less than 180 degrees.

Oil Can - A localized out-of-flat condition often seen as buckles toward the center of an otherwise flat sheet.

Outside Diameter - The distance between the outer walls of a pipe. Used as the standard measure for ACR tubing.

Oxidation - The process by which the oxygen in the air combines with metal to produce tarnish and rust.

PSI - Pounds per square inch.

Package System - An air-conditioning system which is a self-contained unit, located outside the area to be heated or cooled. The conditioned air is directed into and out of the unit by return and supply ducts which penetrate the wall or roof of the structure.

Paintgrip - See Zincgrip.

Pallet - A portable wooden platform that supports heavy or bulky items such as steel or roofing materials.

Parallel - Two straight lines in the same plane that do not intersect.

Perforated - Patterned holes placed in sheet metal to allow for venting or for acoustical purposes.

Perimeter Air Distribution - A system of distribution where air outlets are located around the perimeter of the building. The outlets may be located in either the floor or the ceiling.

Perm - Unit of water vapor transmission. Defined as one grain of water vapor per square foot per hour per inch of mercury pressure difference (1 inch of Mercury = 0.491 PSI). The formula per perm is: P = grains of water vapor/square foot x hour x inch Mercury).

Perpendicular - Two lines that intersect at a 90 degree angle.

Personal Protective Equipment - Pieces of equipment or clothing designed to prevent or minimize the effect of injuries.

Pexto - The original bar folder was invented by Edward Converse and patented by Seth Peck of Peck, Stowe & Wilcox. The company was later known as "Pexto" until it was purchased by Roper-Whitney.

Physical Properties - The properties other than mechanical properties that pertain to the physics of a material; for example, density, electrical conductivity, thermal expansion, etc. Often improperly used to express mechanical properties.

Pickle Patch - A tightly adhering oxide that was not removed during the pickling process.

Pickling - The removal of surface oxides from sheets by chemical or electro-chemical reaction.

Piers - Any of various vertical supporting structures.

Piping Symbols - Symbols for piping used to contain gas, oil, steam heat, and conduit wiring.

Pittsburgh Lock - A corner-locking longitudinal seam where a right angle flange is inserted into a formed pocket flange flattened over the right angle flange.

Place Value - The exact quantity of digit determined by its place relative to the decimal point.

Plan - The top view of a building or object from about four feet above the level shown.

Plenum - A pressure-equalizing chamber used in air distribution systems.

Plumb - Perfectly vertical.

Pneumatic - Operation by air pressure.

Pneumatic tools - Air powered tools. Electric or gasoline powered compressors produce the pneumatic pressure.

Points - Teeth per inch on a handsaw.

Product - The answer in a multiplication problem.

Proper Fraction - A fraction where the numerator is smaller than the denominator.

Psychrometer - Instrument for measuring relative humidity.

Psychometric Chart - A graphical representation of the properties of air.

Psychrometry - The study of air and its properties.

Punch - The male part of a tool that forces a slug of scrap material through a die, leaving a hole of a prescribed shape and size.

Purging - The act of blowing non-condensing gases out of a refrigeration system.

Quotient - The answer in a division problem.

R.P.M. - Revolutions per minute.

R-Value, R-Factor - A measurement of resistance to heat flow. R-value is measured in terms of the total performance of the insulating material. It is the reciprocal of the C-factor. A product with an R-value of 5.14 has a C-factor of 0.195 (1 divided by 5.14). The higher the R-value, the more insulating value. See also C-factor, K-factor, and U-factor.

Radius - The length of a line segment from the center of a circle to the circumference. Half the length of the diameter.

Reciprocate - To move alternately back and forth.

Reclamation - Remanufacture of used refrigerant to bring it up to the standards required of new refrigerant.

Recoiler - The apparatus used to recoil a metal strip after it is processed.

Recovery - The removal and temporary storage of refrigerant in containers approved for that purpose.

Refrigerant - A substance used in a refrigeration system to pick up heat in the evaporator and discharge it in the condenser.

Refrigeration cycle - The process by which circulating refrigerant absorbs heat from one location and transfers the heat to another location.

Register - A covering for the termination of an HVAC duct with a closeable damper to regulate airflow. It has bars or vanes which help direct the airflow in a predetermined pattern.

Reinforcing - Usually heavier pieces of metal shaped to form 90-degree angles that have been fastened to sheet metal at intervals to add rigidity to the sheet. Reinforcing may be either exposed or on the inner side.

Relative Humidity - The amount of moisture in the air in relation to the capacity of the air to hold moisture.

Relay - A magnetically-operated device consisting of a coil and one or more sets of contacts. Used in low current circuits.

Remainder - Left over amount in a division problem.

Respirator - A device designed to provide clean, filtered air for breathing no matter what is in the surrounding air.

Right Angle Flange - A straight-edge sheet folded 90 degrees.

Rockwell Hardness Test - A standard method for measuring the hardness of metals. The hardness is expressed as a number related to the depth of residual penetration of a steel ball or diamond cone "brale."

Roll Former - A series of mechanically driven roller dies capable of converting flat sheet metal to a profile configuration.

Roll Forming - Shapes made from a flat product by passing it between multiple stands of contoured rolls. Generally, the corners are not as sharp as those achieved in extrusion.

Roller Levelers - A series of small diameter staggered rolls used primarily to improve flatness and/or to remove yield point elongation.

Rolling Oils - Lubricants used during roll forming.

Roof Flashing - Metal, or other material, used to waterproof roof joints or openings where penetrations occur on a roof or where there is a change in a plane such as a wall.

Roof Plan - A view of the roof level of a building, taken from directly above the roof, usually showing perimeter treatments, penetrations, roof top equipment, roof drains, skylights, hatches, etc.

SBCC - Southern Building Code Congress. Publishes the Standard Building Code.

Salt Spray Test - An accelerated corrosion test in which the metal specimens are exposed to a fine mist of salt water either continuously or intermittently (ASTM B117).

Scaffold - An elevated work platform for both personnel and materials.

Scaffolding - A manufactured or job-built structure that supports a work platform.

Scale - 1. Metal - Oxides of iron which form on the surface of hot steel. 2. Architectural - The ratio between the size of an object being drawn and its actual size. Also, a measuring device used for laying off distances.

Schedule - Tables containing information that describes and specifies the types of items required for the construction of a building.

Seasonal Energy Efficiency Ratio - The total cooling of an air conditioner or heat pump in BTU's during its normal annual usage period for cooling divided by the total electrical energy input in watt-hours during the same period.

Secondary Air - Air that is added to the mix of fuel and primary air during combustion.

Sectional Drawings - A cutaway drawing showing the inside of an object or building.

Self - Priming - In pumping technology, a pump that creates a vacuum or suction in the impeller housing (volute) and which has the ability to lift a fluid (positive displacement).

Sensible Heat - Heat that can be measured by a thermometer or sensed by touch. The energy of molecular motion.

Shot Blasting - The cleaning of a metal surface by air blast using metal shot as an abrasive.

Skid - A portable wooden platform that supports heavy or bulky items such as steel or roofing materials.

Slitting - A process by which wide sheet is slit or cut into narrower widths.

Slug - The material ejected from a punch and die forming operation.

Snap Lock - A corner-locking longitudinal seam where a right angle flange containing notches at 2 inch intervals is inserted into a preformed pocket with a 180 degree open hem. When fully inserted, the right angle flange snaps behind the open hem, forming a tight-fitting longitudinal seam.

Solder - A fusible alloy used to join metals.

Soldering - A relatively low temperature joining process, the lowest of the three, using lead-base or tin-base alloy solder filler metals which melt below 500 Fahrenheit. The solder is drawn between the closely fitted surfaces of the joint by capillary action.

Solenoid - An electromagnetic coil used to control a mechanical device such as a valve or relay contacts.

Solid Content - The amount of solids suspended in liquid carrier (water or solvent). When the carrier dries (evaporates or "flashes off"), the solids remain behind as the finished product. Solid content is important in adhesives and duct sealers; the higher the percentage, the more usable product is available.

Sones - A measurement of sound; the greater the sones, the louder the sound.

Spangle - The characteristic crystalline form in which the hot dipped zinc coating solidifies on the steel surface.

Specification Sheet - Also called specs. The written (usually typed) requirements issued by architects or engineers to establish general conditions, standards, and detailed instructions which are used with the blueprints.

Spillage - Combustion products flowing from the appliance air openings or draft hood relief openings due to a malfunction of the venting system.

Spinning - Forming sheet metal by bending or shaping it under pressure applied by a smooth hand tool or roller while the metal is revolved rapidly.

Split System - An air-conditioning system which has two main components, an outside condenser and an indoor evaporator.

Spread - Width of the air pattern at specified throw.

Stamping - Bending, shaping, cutting out, indenting, embossing, coining or forming metal by means of shaping dies in a press or power hammer.

Standard English Ruler - Instrument that measures in English units (inches, feet, yards).

Standing Seam - An unsoldered longitudinal seam that permits limited expansion and contraction. Formed by abutting two right angle flanges with one flange 1/4 inch higher than the second flange. The long flange is turned over the shorter flange 180 degrees and button punched at intervals to provide a method of fastening. In some cases a second fold is made by turning both flanges inward another 180 degrees; if this type is used the button punch is omitted. The double seam is used for roof and architectural applications.

Static Pressure - A normal force exerted on a moving fluid (air) which tends to burst the duct (if a positive pressure) or to collapse the duct (if a negative pressure). Supply trunk static pressure usually is stated for the point where the duct pulls off the supply plenum.

Stepladder - A self-supporting ladder consisting of two elements hinged at the top.

Storm Collar - A cone-shaped metal piece providing a waterproof transition from a vent pipe and a roof where the pipe emerges from the roof.

Straight Ladder - A non-adjustable ladder of fixed length.

Stretcher Leveling - A method of producing extreme flatness in sheets by stretching them.

Stretcher Strains - Irregular surface patterns which develop during drawing.

Strippable Film - A protective film over prefinished metal sheet. There are two versions of strippable film. One is applied in liquid form during the coil coating process. The other form is an adhesive film which is post applied to a prefinished product.

Structural - A term that means that a given product can stand on its own merit load wise.

Stucco Embossed - The coining of a sheet metal surface for the purpose of diffusing the reflection of light. In metal roofing this helps reduce the visual impact of oil canning. This is a cold form process done via mating drum rollers after the coil coating process but prior to the forming of the metal roof panels.

Studs - Upright pieces in the outer or inner walls of a building to which panels, siding, etc. are nailed.

Subcooling - The temperature of a liquid when it is cooled below its condensing point.

Submersible Pump - A pump which is designed to operate under the surface of a fluid.

Suction Line - The low-pressure refrigerant line connecting the direct expansion cooling coil to the low side of the compressor.

Sum - The answer to an addition problem.

Superheat - The measurable heat added to the vapor or gas produced after a liquid has reached its boiling point and completely changed into a vapor.

Supply Air System - Air being delivered through a duct system to selected areas. The air may or may not have been fully conditioned, but in general, will have been passed through air filters.

Swaged Joint - A method of creating a pipe joint in which the diameter of one of the pipes to be joined is expanded using a special tool. The other pipe then fits inside the swaged pipe.

Sweating - A method of joining pipe in which solder is applied to the joint and heated until is flows into the joint.

TCS - See Terne Coated Stainless Steel.

TDC - Transverse Duct Connector- A roll-formed operation performed on the ends of metal duct; produces a right angle flange which can be mated to another piece of duct with the same profile. Proprietary product of Iowa Precision Industries (IPI). Competes with TDF (Engel) and Ductmate 4-bolt connector.

TDF - Transverse Duct Flange - A roll-formed operation performed on the ends of metal duct; produces a right angle flange which can be mated to another piece of duct with the same profile. Proprietary product of Engel Industries. Competes with TDC (IPI) and Ductmate 4-bolt connector.

T-Bend Test - Bending metal 180 degrees with an internal diameter equal to xt where t = metal thickness.

Takeoff - The process of surveying, measuring, itemizing and counting all materials and equipment needed for a construction project as indicated by the drawings.

Tee - Pipe fitting shaped like the letter T. Each leg of the tree can be joined at a pipe or another fitting.

Telescoping - Transverse slipping of successive layers of a coil so that the edge of the coil is conical rather than flat.

Temper - The condition produced in a metal by mechanical or thermal treatment and having characteristic structure and mechanical properties.

Temper Rolling - Light and cold rolling sheet steel. This operation is performed to improve flatness, to minimize the tendency to stretch, strain and flute, and to obtain the desired texture and mechanical properties.

Tempered - A heat treatment used to create or restore hardness in steel.

Tensile Strength - Also called ultimate strength - The breaking strength of a material when subjected to a tensile (stretching) force. Usually measured by placing a standard test piece in the jaws of a tensile machine, gradually separating the jaws, and measuring the stretching force necessary to break the test piece. Tensile strength is commonly expressed as pounds (or tons) per square inch of original cross sectional area.

Terne - Prime copper bearing steel coated both sides with Terne alloy (80% lead, 20% tin). Terne is typically used for standing, batten, and flat seamed roofs as well as for architectural sheet metal applications.

Terne Coated Stainless Steel - TCS is type 304 stainless steel coated both sides with terne alloy (20% tin, 80% lead). The terne coating provides a slate gray appearance, while the stainless steel base sheet is highly resistant to corrosion. The product is used for standing, batten and flat seamed metal roofs as well as for architectural sheet metal applications.

Thermal Overload Protection - A device which prevents motor burnout if an air-conditioning system or pump operates improperly. The overload circuit is attached in series with a motor coil, and when excessive heat occurs, the thermal overload opens, breaking the electrical circuit. When the motor cools, the overload returns to the normal (closed) position and restarts the motor. A motor operating under overload protection should be checked.

Thermocouple - A device made of two different metals that generates electricity when there is a difference in temperature from one end to the other.

Thermometer - An instrument for measuring temperature.

Thermostat - A temperature-sensing control device.

Thimble - A metal device penetrating a wall with a hole for a vent pipe to pass through. The thimble secures the pipe, seals the wall opening, and ensures that the hot vent is isolated from combustible material.

Throw - The distance air travels until velocity drops below 75 feet per minute.

Tolerance - The upper and lower limits of a size of specification.

Ton of Refrigeration - Large unit for measuring the rate of heat transfer. One ton is defined as 12,000 BTU's.

Tool Steel - Special alloy steel that combines different elements to produce a steel that is extremely hard and tough after heat treatment.

Topographic - The physical features of an area.

Torque - A measurement of force used to describe the "twisting power" of power tools. Usually measured in foot/pounds.

Total Elongation - Percent elongation measured after fraction in a tension test.

Total Heat - Sensible heat plus latent heat.

Transformer - Two or more coils of wire wrapped around a common core. Used to raise and lower voltage.

Transition - a) The process of going from one plane to another.

b) A sheet metal fitting that adapts from one size to another (12x8 to 10x8).

Transverse - Lateral or crosswise. The side to side dimension of an object.

Transverse Drawing - A section showing where the "cut" is made along the short dimension of the building.

Transverse Duct Joints - Those points where one duct section is joined to a fitting or another duct section.

Trigger lock - A small lever or part which when pulled or pressed releases or activates a locking catch or spring.

Tubing - Thin wall pipe; generally, pipe that can be easily bent.

Turning Vanes - Rigidly installed curved metal air guides placed in elbows, stack heads, etc. to produce a uniform air pattern through the fitting.

U - Factor - A measurement of resistance to heat flow. The U-factor is the total of all the insulating components in a given assembly (total of all C-values). It can be expressed as a reciprocal of R-value (an assembly with two layers of insulation, each having an R-value of 5.6, has a total R-value of 11.2, or a U-factor of 0.089). The lower the U-factor, the more the insulating value. See also R-value, K-factor, and C-factor.

Ultimate Strength - See Tensile Strength.

Uncoiler - An apparatus at the beginning of the coil line used to payoff the strip or coil.

Underwriters Laboratories - UL is an independent testing agency that tests a wide range of products and assemblies for various traits (especially fire resistance) according to established tests (usually ASTM's).

Union - Pipe fitting used to join two lengths of pipe. It permits disconnecting the two pieces of pipe without cutting it.

Unit Heater - A manufactured product for direct heating of air, designed primarily for support from the ceiling, and when used in these specifications. It generally does not apply to applications where ductwork is used.

Updraft - An increase in the upward velocity and volume of flue gases caused by excessively low atmospheric pressures at the outlet of the chimney or vent cap.

Vapor Barrier - A membrane, usually foil or plastic, that prevents the flow of vapor pressure driven moisture.

Velum - An original drawing, from which blueprints and working drawings are duplicated. Velum is a thin, translucent paper, typically with black ink. This process is used less often now that large scale photocopying is available.

Vent - An opening designed to convey water vapor or other gas from inside a building or a building component to the atmosphere.

Vent Connector - That portion of the venting system which connects the gas appliance to the gas vent or chimney

Vent Gases - Products of combustion from gas appliances plus excess air and dilution air in the venting system above the draft hood or draft regulator.

Vent Terminal - The fitting at the end of a vent pipe that directs the vent gases into the outside atmosphere and keeps out rain, snow, debris, and animals.

Ventilation - A process of supplying or removing air by natural or mechanical means to or from any space. This air need not have received any of the treatments described under the definition for air conditioning.

Ventilation/Makeup Air - Air brought into or allowed to enter the space occupied by an appliance to replenish air used in combustion and draft hood dilution.

Viscosity - The internal resistance to flow exhibited by a fluid.

Volume Dampers - A damper designed to control the direction and quantity of air flow within a duct system.

Wavy - Not flat. A slight wave following the direction of rolling.

Weather tight Joint - Joint formed in such a manner as to resist moisture penetration when exposed to maximum wind and rain (or snow) conditions occurring during the most severe weather conditions normally encountered in the area of the installation.

Welding - A high temperature and/or pressure joining process involving fusion of the base metals with or without the addition of filler metal.

Whip - A preassembled wire and conduit for connection of outdoor condensers and heat pumps to the electrical disconnect box.

Whole Numbers - Complete units without fractions or decimals.

Work Hardening - Increase in resistance to deformation (i.e., in hardness) produced by cold working in sheet metal.

Working Drawings - Drawings used in actual construction of a building or part of a building. Also referred to as "Blueprints" and "Construction Drawings."

Yield Point - The stress beyond which the metal is permanently deformed.

Yield Strength - In steel, the force that a product can withstand before it is permanently deformed or shaped. Expressed in PSI.

Zincgrip - Armco AK Steel's trade name for a hot-dipped galvanized coating that is phosphatized for paintability.

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