HVAC TERMS & DEFINITIONS
A.S.T.M.
Standards issued by the American Society of Testing Materials
ACCA
Air Conditioning Contractors of America.
Access Door
A closure for an opening or hole in the duct that allows the user access to the inside of the ductwork usually for cleaning.
Adjustable Elbow
A round elbow manufactured with elbow lock seams that can be adjusted to meet multiple angles.
Air Conditioner
A device used to control temperature, humidity, and cleanliness of air in a conditioned space.
Air Conditioning
Control of the temperature, humidity, air movement, and cleaning of air, in a confined space.
Air Diffuser
Grille designed to direct airflow in the desired pattern.
Air Handler
Parts of a system including the fan-blower, filter and housing. The portion of the central air conditioning or heat pump system that moves heated or cooled air throughout a home’s ductwork. In some systems, a furnace handles this function.
ARI
Air Conditioning and Refrigeration Institute.
Ashrae
American Society of Heating, Refrigeration and Air Conditioning Engineers.
Backdraft Damper
A damper with blades actuated by gravity, spring loading or counterbalancing, permitting air to pass through them in one direction only.
Bird Screen
A versatile product that can be used in a variety of commercial, residential and industrial applications. Primarily used in the HVAC industry as a means to keep birds, rodents and other creatures out of exterior openings in duct systems.
Blast Gate
Blast gates are used to focus a dust collection system’s vacuum pressure for maximum dust (or other material) extraction at the desired location. Blast gates are positioned near individual pieces of machinery and operate by being, by default, closed — blocking air flow. When one blast gate is opened, all available suction is focused at that location, maximizing the amount of material collected.
BTU
British Thermal Unit. Measures the amount of heat required to raise or lower the temperature of one pound of water one degree Fahrenheit.
Bullnose Tee
A tee with a branch with a larger diameter than the main. For example an 8/8/12.
Burner
The device that facilitates the combustion of air and gas.
Butyl Gasket
A one-component non-drying permanently flexible material designed for sealing rigid and expansion joints between wood, glass, metal and masonry surfaces without a primer.
Canvas Connector
Also known as a flex connection, the canvas connector is a strip of metal followed by a strip of canvas material followed by another strip of metal. Utilized to isolate vibration and thus noise from the unit to the ductwork.
Carbon Monoxide
Colorless, odorless and poisonous gas (CO) produced when carbon or carbonaceous fuels are burned with too little air.
Celsius
A temperature scale that registers the freezing point of water as 0° and the boiling point as 100° under normal atmospheric pressure.
Centimeter
A metric unit of linear measurement which equals .3937 inches.
CFM
Cubic Feet per Minute. A measurement of airflow volume.
Chiller
A heat exchanger using air, refrigerant, water and evaporation to transfer heat (BTUs) to produce air conditioning (measured in tons). A chiller is comprised of an evaporator, condenser and compressor system.
Comfort Zone
Area on psychometric chart which shows conditions of temperature, humidity and sometimes air movement in which most people are comfortable”
Companion Ring
A heavy-duty ring usually constructed of black iron used to connect pipe and fittings. Can be swedged, tack welded or fully welded onto pipe or fittings.
Compressor
A mechanical device where the refrigerant is compressed from a lower pressure and lower temperature to a higher pressure and higher temperature. The compressor maintains a low pressure in the evaporator by continually removing refrigerant vapors. This low-pressure, low-temperature vapor is then compressed into a higher pressurize, hot refrigerant vapor which leaves the compressor and travels to the condenser. The motor in the compressor is the main consumer of energy in the chiller system. The energy used by the compressor is dependent on the pressure increase. The head pressure divided by the suction pressure or the condenser pressure divided by the evaporator pressure expresses this. If the compressor operates out of its original design, it will affect energy consumption.
Concentric
Centered
Condensate
A fluid formed when a gas is cooled to its liquid state
Condensation
Liquid or droplets which form when a gas or vapor is cooled below its dew point
Condenser
The part of a refrigeration mechanism which received hot, high-pressure refrigerant gas from the compressor and cools gaseous refrigerant until it returns to a liquid state”
Condensor Fan
Electric motor and fan blade used to move air through air-cooled condenser
Conical
A tap or takeoff increasing in size at the base to maximize airflow.
Contractor
A switch that can repeatedly cycle, making and breaking an electrical circuit. When sufficient current flows through the A-coil built into the contractor, the resulting magnetic field causes the contacts to be pulled in or closed.
Damper
A damper is a valve or plate that stops or regulates the flow of air inside a duct, chimney, VAV box, air handler, or other air handling equipment. A damper may be used to cut off central air conditioning (heating or cooling) to an unused room, or to regulate it for room-by-room temperature and climate control. Its operation can be manual or automatic. Manual dampers are turned by a handle on the outside of a duct. Automatic dampers are used to regulate airflow constantly and are operated by electric or pneumatic motors, in turn controlled by a thermostat or building automation system.
Dehumidifier
A device that removes humidity, or moisture, from the air.
Dieform
A two-piece stamped elbow that is welded together on the throat and heel to make it airtight.
Diffuser
A grille over an air supply duct with vanes that distribute the discharging air in a specific pattern or direction.
DOE
Department of Energy.
Double Wall Duct
Ductwork that is fabricated from 2 layers of metal with a layer of insulation in between. The inner wall may be perforated for sound attenuation or solid to prevent thermal loss. A layer of film may be added in some cases to ensure no insulation enters the air stream.
Drain Pan
Also a condensate pan. As the refrigerant vapor is liquefied, the drain pan collects the condensate and funnels it to the drain line.
Duct Cap
A reusable plastic bag with an elastic band sewn on the open end. The duct cap will keep dust and other construction debris out of the ductwork during the construction process.
Duct Sealer
A caulking either water or solvent-based that when applied to connections or penetrations in HVAC systems seals gaps to ensure a minimum of air leakage.
Ductwork
A network of metal, fiberboard or flexible material flowing throughout a space which delivers air from an HVAC unit to the respective zones of a home or office.”
Eccentric
Circle or disk mounted off-center on a shaft
Egg Crate – (Aluminum Louvers)
Open grid design allowing use in air ventilation applications and for concealing fire sprinkler systems.
Evaporation
A term applied to the changing of a liquid to a gas. Heat is absorbed in the process.
Evaporator
Part of a refrigeration mechanism in which the refrigerant vaporizes and absorbs heat.
Evaporator Fan – Fan which increases airflow over the heat exchange surface of evaporators.
E-Z Flange
A system used to connect spiral pipe and fittings through the use of flanges, gasket and barrel clamps.
E-Z Tap
The E-Z Tap takeoff collar has a one inch flange turned out. This one-piece design add rigidity to the collar. There is a double faced gasket applied to the flange to assure a tight seal. Just peel, stick and fasten with sheet metal screws.
Fahrenheit
A temperature scale in which water freezes at 32 degrees and boils at 212 degrees at normal atmospheric pressure.
Fahrenheit Scale
On a Fahrenheit thermometer, under standard atmospheric pressure, boiling point of water is 212 degrees and freezing point is 32 degrees above zero”
Fan
A device that creates air flow.
Fan Coil
An indoor component of a heat pump system, used in place of a furnace, to provide additional heating on cold days when the heat pump does not provide adequate heating.
Filter
A device that acts as a strainer to remove dirt or undesired particles.
Flat Oval Ductwork
Designed for restricted space conditions that cannot accept round spiral ductwork, flat oval duct is stretched with radius sides and a flat top and bottom.
Freon
Trade name for a family of synthetic chemical refrigerants manufactured by E.I. du Pont de Nemours & Co., Inc.
Full Saddle
A saddle with a large flange usually 2.5 to 3 inches to connect it to the main pipe.
Furnace
The major component in heating a home. A device that facilitates the combustion of fuel and air to create heat.
Galvanic
Action Wasting away of two unlike metals due to electrical current passing between them. The action is increased in the presence of moisture.
Gasket
Resilient(spongy) or flexible material used between mating surfaces of refrigeration unit parts, or on doors to give a leak-proof seal.
Gasket Foam
Joint sealing material made of rubber or plastic foam strips.
Gasketed Connection
A spiral ductwork connection that utilizes a factory-installed rubber gasket on the fittings to seal the ductwork.
Gauge Compound
An instrument for measuring pressures both above and below atmospheric pressures
Gorelock
An airtight standing seam connection used to join gores of elbows or other fittings.
Heat
Form of energy which acts on substances to raise their temperature; energy associated with random motion of molecules
Heat Exchanger
Device used to transfer heat from a warm or hot surface to a cold or cooler surface. (Evaporators and condensers are heat exchangers).
Heat Pump
Compression cycle system used to supply heat to a temperature-controlled space. Same system can also remove heat from the same space
HETO
High-Efficiency Takeoff. This tap used on rectangular duct is designed with an increase on the upstream side of the fitting, this design allows the maximum amount of air to flow downstream making the system much easier to balance and saves energy.
High-Efficiency Air Cleaner
An air filter installed in your central system that collects up to 99% of particles 5 microns or larger. In comparison, your standard air filter only picks up about 8% of these same particles.
Humidity
Moisture. Dampness in air.
HVAC
Heating, Ventilation and Air Conditioning.
Kilometer
A metric unit of linear measurement = 1000 meters.
Louvers
Louvers are very similar to dampers except that the slats or vanes are usually fixed and non-adjustable. Louvers are normally installed into a wall or other location to provide positive ventilation for a room or enclosed area. Louvers are available in all shapes, sizes and flow capabilities. They are typically fabricated from aluminum or galvanized steel.
Media
The fine material of a filter that traps dirt, dust, mildew and bacteria.
Mitered Elbow
An elbow that has a sharp 90-degree turn with no radius.
NEBB
National Environmental Balancing Bureau.
Neoprene
Synthetic rubber which is resistant to hydrocarbon oil and gas
Nonferrous
Group of metals and metal alloys which contain no iron
Operating Cost
The day-to-day cost to run your home comfort system, based on the energy required to run it.
Operating Pressure
Actual pressure at which the system works under normal conditions. This pressure may be positive or negative (vacuum).
Opposed Blade Damper
A damper, 1 through which the airflow is adjusted by means of two sections of damper blades on a common linkage, arranged so that adjacent blades rotate in opposite directions.
Orifice
An opening or hole.
Paint Grip
Also known as Galvanealed or Paint Lock material. Paint grip material is carbon steel coated with zinc on both sides by the continuous hot dip process and then subjected to an in line heat treatment that converts the entire coating to a zinc-iron alloy. This results in a matte finish which makes the steel suitable for painting without further treatment.
Pair of Pants
Also known as a “Y” fitting because of its shape, the pair of pants fitting is a main going in and two branches coming off at either 45 or 90-degree angles in relation to the main.
Parallel Blade Damper
A damper, 1 through which the airflow is adjusted by means of sections of damper blades on a common linkage, arranged so that adjacent blades rotate in parallel direction.
Pookie
HVAC slang term for duct sealant.
Pressure
The application of force to something by something else in direct contact with it.
Pressure Gauge
An instrument that measures pressure in psig, psid or psia depending on the circumstances.
PSI
Symbol or initials used to indicate pressure measure in pounds per square inch absolute. Absolute pressure equals gauge pressure plus atmospheric pressure
Pump
Any one of the various machines which force a gas or liquid into — or draw it out of – something as by suction or pressure.
PVC
PolyVinyl Chloride. A coating added to galvanized metal that gives it added resistance to chemicals and moisture.
R-22
Monochlorodifluoromethane…Low temperature, used in HVAC and occasionally coolers.
Radiant Heating
A heating system in which warm or hot surfaces are used to radiate heat into the space to be conditioned.
Radius Elbow
An elbow that has a rounded throat and heel.
Rain Cap
Also known as a china cap, the rain cap is used at the top of a round stack to keep rain and snow from entering the pipe.
Refrigerant
A substance used in a refrigeration mechanism. It absorbs heat in evaporator by a change of state from a liquid to a gas and releases its heat in a condenser as the substance returns from the gaseous state back to a liquid state
Register
Combination grille and damper assembly covering an air opening or the end of an air duct
Register Takeoff
A box that mounts on round pipe allowing a rectangular register to be installed to it.
Seal
A seal is a tight and perfect closure (as against the passage of gas or water) or a device to prevent the passage or return of gas or air into a pipe or container.
SEER
Seasonal Energy Efficiency Ratio. A rating system developed by the U.S. Government to indicate the efficiency level of cooling equipment.
Sensor
A device that reacts to a change in conditions.
Shoe Tap
A takeoff that is increased on the upstream side of the fitting.
Single Blade Damper
A damper through which the airflow is adjusted by means of a single blade or piece of metal on a single shaft.
Single Wall Duct
Ductwork that is fabricated with a single layer of metal.
Sky Blast
Semi-circular flaps (butterfly damper) cover the exhaust stack when the fan is off. When the fan is on, flaps are forced out of the way to provide a clear path for air movement. A built-in gutter system is designed to prevent rain and snow from entering the stack. Made from galvanized spiral pipe for strength and durability.
Slip and Drive
A transvers connection for rectangular duct and fittings by means of a drive cleat and a slip. On the drive, the ends are mated together and the drive cleat is pounded on from one end. On the slip, the ends of the duct are inserted into the open ends of the s-shaped piece.
SMACNA
Sheet Metal and Air Conditioning Contractors National Association
SPIDA
Spiral Duct Manufacturers Association
Spiral Pipe
Round ductwork formed from a coil of metal into a rigid tube with a 4-ply lockseam. It has a smooth interior for low friction loss with the grooved seam entirely on the outside. The pipe has a resistance to crushing approximately 2.5 times that of longitudinal lockseam or welded pipe.
Split System
An outdoor unit combined with an indoor unit.
Squirrel Cage
Fan which has blades parallel to the fan axis and moves air at right angles or perpendicular to the fan axis
Standoffs
Or insulation standoffs are used to extend damper handles so they remain accessible when ductwork is wrapped with insulation.
Swedged Saddle
A takeoff that has a 5/8″” flange to connect it to the main pipe.
SWMIA
Sheet Metal Workers International Association
TABB
Testing Adjusting and Balancing Bureau
TDC
Transverse Duct Connection is a connection system for rectangular ductwork that is formed directly onto the ductwork. This provides a solid metal connection that reduces leakage. Used in leau of external 4 bolt add ons TDC saves the time of cutting, assembling and installing a separate flange. A TDC connection is completed by installing the corners, applying gasket to the flange, mating it to another flange, placing nuts and bolts in the corners, and installing cleats at 6″” intervals along the flange. TDF is another variation of this system.
TEK Screws
Self-drilling screws are similar to sheet metal screws but have a drill point instead of coming to a sharp point and will drill their own hole. This eliminates the need to pre-drill a pilot hole.
Temperature
Degree of hotness or coldness of an object or location measured on a definite scale.
Temperature-Humidity Index
Actual temperature and humidity of air sample compared to air at standard conditions.
Thermal Relay
Heat-operated electrical control used to open or close a refrigeration system electrical circuit. This system uses a resistance wire to convert electrical energy into heat energy.
Thermometer
Measures and evaluates temperature.
Thermostat
Sensors that monitor and control the output of an HVAC system.
Ton of Refrigeration
Refrigerating effect equal to the melting of 1 ton of ice in 24 hours. This may be expressed as follows: 288,000 Btu/24 hr., 12,000 Btu/1 hr, 200 Btu/min.
Transition
A fitting that increases or decreases the duct size.
Turning Vane
Turning vanes are curved fins of metal placed inside ductwork where air is changing direction, used to promote a more uniform airflow and decrease turbulence Turning vane and rail are recommended for use in square throat elbows and tees. When using turning vane and rail performance is greatly enhanced in the HVAC system.
Vacuum
A space where the pressure is significantly below that of standard atmospheric pressure.
Zip Screws
Self-drilling screws that come to a sharp point allowing the screw to penetrate the metal easily which eliminates the pre-drilling of holes.
Zoning
A system that divides a home, office, or space into different regions in order to better control the temperature and effectiveness of a heating and cooling system.
© 2017 Sheet Metal Connectors, Inc.
