HVAC Terms in Plain English

SEER2: The efficiency rating of an air conditioner. Higher number, lower electric bill. Texas requires at least 14.3 on a new system; 16 to 18 is the premium range.
Ton: How much cooling a system can do, not what it weighs. One ton handles roughly 600 square feet in most of Texas, so homes usually need 2 to 5 tons.
Manual J: The calculation a good contractor does to work out what size system your house actually needs, from your insulation, windows and layout rather than a rule of thumb. Ask for it in writing.
Matched system: Indoor and outdoor units designed to work together. Replace only one side and the pair usually no longer matches, which costs efficiency and can void the warranty.
AHRI certificate: A certificate showing the indoor and outdoor units were tested together as a pair. Rebates and warranties usually require it.
Refrigerant (R-22, R-410A, R-454B): The gas that carries heat out of your house. R-22 is the old kind, no longer made and expensive to top up. R-410A is in most systems since about 2010. R-454B is the new standard on 2025 equipment.
Condenser: The outdoor unit. It holds the compressor and the big fan.
Compressor: The pump inside the outdoor unit that moves the refrigerant. The single most expensive part in the system.
Evaporator coil: The indoor coil that actually cools the air, usually in the attic or in a closet above the furnace. Leaks here are the usual reason a system keeps losing refrigerant.
Air handler: The indoor cabinet with the fan and the coil, for homes that heat with a heat pump or electric heat instead of a gas furnace.
Capacitor: A small electrical part that gives the motors a kick to start. Cheap, and the most common thing to fail in August.
Variable speed (inverter): A system that can run at part power instead of only full blast or off. Quieter, better at pulling humidity out of the air, and cheaper to run.
ECM motor: A newer kind of fan motor that uses a fraction of the electricity of the old kind. Costs more to replace.
AFUE: Furnace efficiency, as the share of the gas that becomes heat in the house. 80% is standard. 96% costs more up front and rarely pays back in a Texas winter.
Expansion valve (TXV): The valve that meters refrigerant into the indoor coil. A stuck one looks a lot like a low charge.
Permit: The city’s sign-off that the work meets code, usually followed by an inspection. The contractor pulls it. Make sure it is in the price.
Like-for-like changeout: Replacing equipment with the same kind in the same place, with no changes to ducts or wiring. Some cities still require a permit for it.
Ductwork: The tubes that carry the air around the house. Leaky or undersized ducts cap what any new equipment can deliver.