Equipment guide
The HVAC glossary.
The ratings and the words you will see on a quote, a label or a technician's report, in plain English. Search the glossary or scan the ratings table.
The ratings
Eight numbers worth knowing.
Efficiency, capacity, airflow and filtration, and what each one tells you about a system.
| Rating | Measures | What it means |
|---|---|---|
| SEER2 | Cooling | How much cooling an air conditioner or heat pump delivers per unit of electricity over a season. Higher is more efficient. |
| AFUE | Furnace heating | The share of a furnace's fuel that becomes heat for the house. 95 percent means 95 percent of the fuel heats the home. |
| HSPF2 | Heat pump heating | Heating efficiency of a heat pump over a season. Higher means less electricity for the same warmth. |
| BTU | Capacity | A unit of heat. Equipment is sized in BTUs per hour. Twelve thousand BTUs per hour is one ton of cooling. |
| CFM | Airflow | Cubic feet of air per minute. Systems are designed around a certain amount of air per ton. |
| MERV | Filtration | How well a filter captures particles of different sizes, on a scale of 1 to 16 for home filters. |
| Static pressure | Duct resistance | How hard the blower pushes against the ducts and filter. High numbers point to restrictions. |
| Temperature split | System health | The difference between the air going into the system and the air coming out of it. |
The glossary
Terms you will hear on site.
Plain-English meanings for words that come up in HVAC estimates and on the job.
- Air handler
- The indoor unit that holds the blower and the cooling coil, and sometimes electric heat. It moves air through the ducts.
- Blower
- The fan inside the indoor unit that pushes air across the coil or heat exchanger and out through the ducts.
- BTU
- A unit of heat. Heating and cooling equipment is sized in BTUs per hour.
- Capacitor
- A small part that gives motors the jolt they need to start and run. A weak one is a common cause of a unit that hums but will not start.
- CFM
- Cubic feet of air per minute, the amount of air a system moves.
- Compressor
- The pump of an air conditioner or heat pump. It circulates the refrigerant and does most of the work.
- Condensate drain
- The line that carries away the water an air conditioner pulls out of the air. A clog can cause leaks and shutoffs.
- Condenser
- The outdoor unit of an air conditioner or heat pump, where heat is released or gathered.
- Damper
- A plate inside a duct that opens and closes to direct airflow, used in zoning systems.
- Dual fuel
- A heat pump paired with a gas furnace, so each runs when it is most efficient.
- Duct
- The tubes, usually sheet metal or flex, that carry conditioned air to the rooms and back.
- Evaporator coil
- The indoor coil where refrigerant absorbs heat and moisture from the air.
- Heat exchanger
- The metal chamber in a furnace that warms the air without mixing it with combustion gases.
- Heat pump
- A system that moves heat instead of making it, cooling the house in summer and heating it in winter.
- Load calculation
- A room-by-room estimate of how much heating and cooling a house needs. It is how equipment should be sized.
- MERV
- A rating of how well a filter captures particles. Higher catches finer particles but adds resistance.
- Mini-split
- A ductless system with an outdoor unit and one or more indoor heads, used for rooms, additions and whole homes.
- Refrigerant
- The fluid that carries heat between the indoor and outdoor units of an air conditioner or heat pump.
- Register
- The cover on a duct opening where air enters a room. Return grilles are where air comes back.
- SEER2
- A seasonal measure of cooling efficiency. Higher means less electricity for the same cooling.
- Short cycling
- When a system turns on and off too often. Oversizing, a dirty filter or a failing part can cause it.
- Static pressure
- A measure of how hard the blower works against the ducts and filter.
- Thermostat
- The control that senses the room and tells the system when to run.
- Two-stage
- Equipment with a low and a high output, so it runs gently most of the time.
- Variable-speed
- Equipment that adjusts its output in small steps to match the need.
- Zoning
- Dampers and thermostats that let different parts of a house be heated or cooled separately.
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