AFUE
Annual Fuel Utilization Efficiency. The percentage of the fuel a furnace burns that ends up as heat in your house rather than going up the flue. A 96% furnace wastes almost nothing.
HVAC terms, A to Z
Our trade is full of acronyms, and a quote covered in them is hard to evaluate. Here is what they mean.
23terms, from AFUE to zoning
A
Air handler
The indoor unit of a split system: blower, coil and filter rack, and usually some electric backup heat. The half that decides whether the ductwork gets the airflow the equipment was rated for.
Auxiliary heat
Electric resistance heat that supplements a heat pump when it cannot keep up. It is effective but expensive, so if it runs constantly, something is wrong.
High energy billsC
Capacitor
A component that gives motors the jolt they need to start and helps them run. It is the most common single failure in HVAC and cheap to replace, and it usually goes on the hottest day of the year.
Ready for maintenanceChangeover temperature
On a dual-fuel system, the outdoor temperature below which the furnace takes over from the heat pump. Set wrongly, it runs the expensive appliance when the cheap one would have coped.
Compressor
The pump at the heart of the refrigeration cycle, and the most expensive single component. Protecting it is why so many other parts have safeties.
Condenser
The outdoor coil, where heat collected from inside is released to the outside air. Keeping it clean and clear is the most useful thing an owner can do outdoors.
AC not coolingD
Defrost cycle
A heat pump periodically reversing to melt ice off its outdoor coil. The steam is normal; a unit permanently encased in ice is not.
Heat pump not heatingDual fuel
A heat pump and a gas furnace sharing one duct system and one thermostat, switching between them at a set changeover temperature. It is often the best arrangement in this climate.
E
ERV / HRV
Energy or Heat Recovery Ventilator. Brings fresh air in and stale air out while transferring most of the heat between the two streams. An ERV also moves some moisture, which suits humid climates.
A healthier homeEvaporator coil
The indoor coil, where refrigerant absorbs heat from your air. It runs cold and wet in summer, which is why it also removes humidity — and why it wants keeping clean.
H
Heat exchanger
In a furnace, the metal wall between combustion gases and the air you breathe. A crack means carbon monoxide can cross that wall, and it is not repairable.
Gas furnace not heatingL
Load calculation
A room-by-room calculation of how much heating and cooling a building needs. The correct basis for sizing equipment, and the step most often skipped.
Selecting a new systemM
MERV
A filter’s efficiency rating. Higher captures finer particles — but a high-MERV filter in a housing not designed for it restricts airflow and does more harm than good.
A healthier homeN
NATE
North American Technician Excellence. Independent third-party certification for HVAC technicians, earned by examination rather than by time served.
R
Reversing valve
The component that lets a heat pump run in both directions. When it sticks, you get heating in July or cooling in January.
Heat pump not coolingR-22
An older refrigerant, no longer produced. Systems using it can still be serviced from reclaimed stock, at steadily rising cost — which makes a leaking R-22 system a strong replacement candidate.
Repair or replace?S
SEER2
The current efficiency rating for cooling equipment: how much cooling you get per unit of electricity under standard test conditions. Higher is better and costs more up front.
Short cycling
Equipment starting and stopping frequently instead of running steady cycles. Usually caused by oversizing or restricted airflow, and hard on the compressor.
Static pressure
Resistance to airflow within the duct system. High static pressure means the ductwork is fighting the blower, and it underlies a great many comfort complaints blamed on the equipment.
Subcooling / superheat
Two measurements used to verify a refrigerant charge properly. Checking both is how a technician confirms the charge is right, rather than adding refrigerant until the air feels cold.
Ready for maintenanceT
Ton
A unit of cooling capacity — 12,000 BTU per hour. A three-ton system is not three tons in weight; the term comes from the cooling effect of melting a ton of ice in a day.
Z
Zoning
Dampers and multiple thermostats letting one system hold different temperatures in different parts of a building. It is the engineered answer to a hot upstairs.
No term matches that. Ask us and we will explain it.
Saw a term on a quote that is not here?
Ask us. We will explain it without trying to sell you anything.
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