HVAC terms, defined
Plain definitions of the HVAC words that come up on estimates, inspections and supplier calls, written for HVAC companies. Each term says where it matters on the job and links the Koira calculator, cost guide or template that goes with it.
A
HVACAFUEAFUE is the annual fuel utilization efficiency of a furnace or boiler: the share of the fuel's energy that ends up as heat in the house over a year.HVACAir handlerAn air handler is the indoor cabinet with the blower and coil that moves air through the ducts, used with heat pumps or with electric heat instead of a furnace.Shared with InsulationAir sealingAir sealing is closing the gaps where air leaks in and out of a house, such as around chimneys, wiring and plumbing holes, top plates, rim joists and attic hatches, with foam, caulk and blocking.
B
Shared with InsulationBlower door testA blower door test uses a calibrated fan in a doorway to pressurize or depressurize a house and measure how leaky it is.HVACBoilerA boiler heats water, or makes steam, and circulates it through pipes to radiators, baseboard or floor tubing to heat a building.HVACBTUA BTU, or British thermal unit, is a unit of heat.Shared with General ContractorBuilding permitA building permit is the local government's approval to do regulated construction work, with inspections at set stages.
C
Shared with Home InspectionCarbon monoxide alarmA carbon monoxide alarm senses the odorless gas from fuel burning appliances, attached garages and blocked vents and sounds an alarm.HVACCFMCFM means cubic feet per minute, the volume of air a fan, register or duct moves.HVACCompressorThe compressor is the pump in a cooling or heat pump system that squeezes refrigerant vapor, raising its pressure and temperature so it can shed heat outside.HVACCondensate lineThe condensate line carries water that drips off the cooling coil, or out of a high efficiency furnace, to a drain or outside.HVACCondenserThe condenser is the outdoor half of a split air conditioner.
D
Shared with Appliance RepairDiagnostic feeA diagnostic fee is the set charge for coming out and finding what is wrong, before any repair is approved.HVACDirect ventA direct vent appliance takes all its combustion air from outside and sends all its exhaust outside through a sealed vent, so it does not use or affect the air in the house.Shared with Kitchen Hood CleaningDuct access panelA duct access panel is a sealed door in a duct that lets cleaners reach the inside to clean it.HVACDuct boardDuct board is rigid fiberglass board with a foil face, cut and folded into rectangular ducts and plenums.HVACDuct damperA duct damper is a movable plate inside a duct that controls how much air flows through that branch.HVACDuct sealingDuct sealing is closing the leaks at duct joints, seams and connections with mastic or approved tape so the air you paid to heat or cool reaches the rooms.
E
HVACEEREER is the energy efficiency ratio of a cooling system at one fixed hot outdoor condition, rather than averaged over a season like SEER.HVACEPA Section 608 certificationThis is the EPA credential, under the Clean Air Act, that a technician needs to work on equipment that can release refrigerant.HVACERVAn ERV is an energy recovery ventilator: a balanced fan unit that brings in fresh air and exhausts stale air while passing heat, and some moisture, between the two streams.HVACEvaporator coilThe evaporator coil is the indoor coil, usually on top of the furnace or in the air handler, where refrigerant boils off and pulls heat and moisture out of the air.Shared with PlumbingExpansion tankAn expansion tank is a small tank with an air cushion that absorbs the extra volume of water as it heats, in a closed water heater or boiler system.
F
H
HVACHard start kitA hard start kit is a capacitor and relay added to a compressor circuit to give the compressor extra torque when it starts.HVACHeat exchangerA heat exchanger is the metal chamber in a furnace that keeps the flame and exhaust gases on one side while house air is heated on the other.HVACHeat pumpA heat pump is an air conditioner that can run in reverse, moving heat into the house in winter and out in summer.HVACHSPFHSPF is the heating seasonal performance factor of a heat pump: heat delivered over a season divided by the electricity used.HVACHVAC maintenance planAn HVAC maintenance plan is a yearly agreement where the customer pays a set price for scheduled tune-ups and gets perks such as priority service or repair discounts.HVACHVAC zoningZoning splits a house into areas with their own thermostats, using motorized dampers and a control panel on one system, or separate systems or mini-split heads.HVACHydronic heatingHydronic heating moves heat with hot water pumped from a boiler through baseboard, radiators or tubing in the floor.
L
HVACLine setA line set is the pair of copper refrigerant lines between the outdoor unit and the indoor coil: a larger insulated suction line and a smaller liquid line.HVACLocking refrigerant capsLocking refrigerant caps are tamper resistant caps on the outdoor service ports of a cooling system, so nobody can open the refrigerant circuit without a special key.
M
HVACMakeup airMakeup air is outside air brought into a building to replace air that exhaust fans or a range hood pull out.HVACManual DManual D is the ACCA method for designing duct systems: sizing trunks, branches and registers so each room gets the airflow its load calls for.HVACManual JManual J is the ACCA method for calculating a home's heating and cooling loads room by room, from its size, insulation, windows, air leakage and climate.HVACManual SManual S is the ACCA method for picking equipment that matches the Manual J loads, using the maker's performance data at the actual design conditions.HVACMERV ratingMERV is the rating for how well an air filter catches particles.HVACMini-splitA mini-split is a ductless heat pump with an outdoor unit piped to one or more wall, ceiling or floor heads inside.
P
Shared with RemodelingPipe chaseA chase is an enclosed vertical or horizontal space framed to hide pipes, ducts or wires as they pass through a building.HVACPlenumA plenum is the box that connects the furnace or air handler to the duct system: a supply plenum on the outlet side and a return plenum on the inlet side.Shared with Property MaintenancePreventive maintenancePreventive maintenance is scheduled inspection and upkeep, like filter changes, gutter cleaning and caulking, done before things break.
R
Shared with TileRadiant floor heatingRadiant floor heating warms a floor with electric heating cable or mats, or with hot water tubing, set under the finished floor.HVACRefrigerantRefrigerant is the fluid that absorbs heat inside the house and releases it outside as it is compressed, condensed and evaporated in a cooling or heat pump system.HVACReturn airReturn air is the air pulled back from the rooms to the equipment to be heated or cooled again, through return grilles and ducts.Shared with General ContractorRough-inRough-in is the stage after framing when plumbing, electrical and HVAC lines are run inside the open walls and floors, before insulation and drywall.
S
HVACSEERSEER is the seasonal energy efficiency ratio of an air conditioner or heat pump: cooling output over a season divided by the electricity used.Shared with Money and paperworkService agreementA service agreement is a contract for recurring work over a set period at a set price, listing the visits, what each covers and how renewal and cancellation work.HVACShort cyclingShort cycling is when a furnace, air conditioner or heat pump turns on and off in short bursts instead of running steady cycles.HVACStatic pressureStatic pressure is the resistance the blower pushes against in the duct system, measured in inches of water column with a manometer.HVACSubcoolingSubcooling is how many degrees the liquid refrigerant leaving the condenser is below its condensing temperature at that pressure.HVACSuperheatSuperheat is how many degrees the refrigerant vapor leaving the evaporator is above its boiling point at that pressure.HVACSupply registerA supply register is the grille where conditioned air enters a room, usually with louvers or a damper to aim or adjust the flow.
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More for HVAC companies: free HVAC tools, templates and guides and how the trade runs on Koira. Or browse the whole glossary.