Reference
HVAC & Refrigeration Glossary
Plain-English definitions of the terms you'll hear from technicians, see on invoices, and read in equipment specs — so you can make informed decisions.
A B C D E H L M R S T W
- AFUE
- Annual Fuel Utilization Efficiency — how efficiently a furnace turns fuel into heat over a season. An 80 AFUE furnace delivers 80¢ of heat per dollar of gas; a 96 AFUE condensing furnace delivers 96¢. Higher AFUE means lower heating bills at a higher equipment cost.
- BTU
- British Thermal Unit — the energy needed to raise one pound of water by one degree Fahrenheit. Used to size heating and cooling capacity. A 36,000 BTU/hour system is a 3-ton AC.
- Commercial Refrigeration
- Cooling systems that keep products at safe, precise temperatures for businesses — reach-in coolers, prep tables, display cases, ice machines, and process cooling. Reliability and fast response matter because downtime means spoiled inventory.
Related: Refrigeration services
- Compressor
- The heart of any AC, heat pump, or refrigeration system — it pressurizes refrigerant so it can release and absorb heat as it circulates. A failed compressor is one of the most expensive repairs, which is why correct charge, airflow, and maintenance matter.
- Condensate Line
- The drain line that carries away moisture the evaporator coil pulls from the air. Algae or sludge can clog it, backing up water and tripping the safety switch — a common cause of a system that suddenly stops cooling. Flushing it during a tune-up prevents the problem.
- Ductless Mini-Split
- A ductless system with one or more indoor air handlers connected to an outdoor compressor. Ideal for additions, shops, garages, server rooms, and spaces that are hard to reach with central ductwork. Installs without ducts and can be zoned room by room.
- EER2
- Energy Efficiency Ratio 2 — cooling efficiency measured at a single high-temperature operating point (rather than across a season like SEER2). It's a useful gauge of performance during the hottest part of a South Texas summer.
- Heat Pump
- A year-round system that moves heat instead of generating it — cooling like an AC in summer and pulling heat from outdoor air to warm the space in winter. It can be far more efficient than electric-resistance or fuel heating in a mild climate like South Texas.
Related: Heat Pump services
- HSPF2
- Heating Seasonal Performance Factor 2 — the efficiency rating for a heat pump in heating mode. Higher numbers mean less electricity used per unit of heat produced. The federal minimum for split-system heat pumps is 8.8 HSPF2 as of 2023.
- Load Calculation (Manual J)
- The industry-standard method (ACCA Manual J) for calculating a building's heating and cooling load based on size, insulation, windows, orientation, and local climate. A correct Manual J is the basis for right-sizing equipment instead of guessing.
- MERV
- Minimum Efficiency Reporting Value — rates how well an air filter captures particles on a 1–16 scale. MERV 8 catches most dust, pollen, and mold spores; MERV 11–13 adds smoke and bacteria-sized particles. A higher MERV can restrict airflow if the system isn't designed for it — ask a technician before upgrading.
- Refrigerant (R-410A / R-454B)
- The chemical that circulates through an AC, heat pump, or refrigeration system to move heat. R-410A was the standard until EPA rules phased it down; newer equipment uses lower-GWP refrigerants such as R-454B. Handling refrigerant requires an EPA Section 608 certified technician.
- SEER2
- Seasonal Energy Efficiency Ratio 2 — the current federal rating for central air conditioner and heat pump cooling efficiency (it replaced SEER in 2023). Higher is more efficient: a 16 SEER2 system uses roughly 20% less electricity than a 13 SEER2 system. In the South-Central region that includes Texas, the minimum for new residential AC is 15 SEER2.
- Short Cycling
- When a system runs briefly, shuts off before the space reaches setpoint, then restarts repeatedly. Causes include an oversized unit, low refrigerant, dirty filters, or a failing control. It wastes energy and wears out the compressor.
Related: Maintenance Plan
- Superheat & Subcooling
- Two measurements technicians use to verify a system is charged correctly. Superheat is how many degrees the refrigerant vapor is above its boiling point leaving the evaporator; subcooling is how many degrees the liquid is below its condensing point leaving the condenser. Correct values mean an efficient, properly charged system.
- Ton (Cooling)
- A measure of air conditioning capacity: one ton = 12,000 BTU/hour. Correct sizing matters — an oversized unit short-cycles and dehumidifies poorly, while an undersized unit runs constantly and never keeps up. Proper sizing uses a load calculation, not square footage alone.
- TXV (Thermostatic Expansion Valve)
- A precision metering valve that controls how much refrigerant enters the evaporator coil based on demand. It improves efficiency and protects the compressor compared with a fixed orifice, and is standard on most modern systems.
- Walk-In Cooler / Freezer
- An insulated, room-sized refrigerated space used by restaurants, grocers, and facilities to store product in bulk. Service covers the refrigeration system, defrost controls, door gaskets, and temperature monitoring to protect inventory and meet food-safety requirements.
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