HVAC, in plain English.

The lingo.

AFUE

Annual Fuel Utilization Efficiency, the percent of fuel a furnace turns into heat. An 80 percent furnace vents through a metal flue; a 95 percent condensing furnace vents in PVC and drains condensate.

Air handler

The indoor unit that moves air in a system without a furnace, typically paired with a heat pump. Contains the blower and evaporator coil.

BTU

British thermal unit, the energy to raise a pound of water one degree. Furnace output and AC capacity are both rated in BTUs per hour.

Condenser

The outdoor unit of a central AC or heat pump: compressor, coil and fan. It rejects the heat pulled from inside the house.

Evaporator coil

The indoor coil, usually sitting on top of the furnace, where refrigerant absorbs heat from the air. A dirty or iced coil is a common cause of weak cooling.

Heat pump

An air conditioner that can run in reverse to heat the house. Modern cold-climate heat pumps hold full capacity well below freezing; a backup heat source covers the coldest days.

HSPF2

Heating Seasonal Performance Factor, the heating efficiency rating of a heat pump. Higher is better.

HVAC

Heating, ventilation and air conditioning: the furnace or heat pump, the air conditioner, the ducts, the thermostat and everything that moves and conditions the air in the house.

Manual J

The industry load calculation that sizes heating and cooling equipment from the house's actual insulation, windows, orientation and climate. A Pro who sizes by square footage alone is guessing.

MERV

The filter efficiency rating, 1 to 16 for residential. MERV 8 to 11 balances filtration and airflow; a very high MERV filter in a system not designed for it starves the blower.

Mini-split

A ductless heat pump with a small outdoor unit feeding one or more wall or ceiling units indoors. Efficient, quiet and ideal for additions, garages and houses without ducts.

Refrigerant

The fluid that carries heat between the indoor and outdoor coils. R-410A is being phased out for lower-warming refrigerants such as R-454B and R-32; a system low on refrigerant has a leak, not a thirst.

SEER2

Seasonal Energy Efficiency Ratio, the efficiency rating on a central air conditioner or heat pump under the current federal test. Higher is more efficient; 14 to 15 is minimum, 18 and up is high efficiency.

Short cycling

Equipment that turns on and off every few minutes instead of running full cycles. Causes include oversizing, a bad thermostat, a clogged filter or a failing component.

Static pressure

The resistance the blower works against in the ductwork. High static pressure means undersized or restricted ducts, and it shortens equipment life.

Ton

A measure of cooling capacity, not weight. One ton removes 12,000 BTUs of heat per hour. A typical house needs one ton per 400 to 700 square feet depending on climate and insulation.

Variable speed

Equipment whose compressor or blower runs at many speeds instead of just on or off, holding steadier temperatures and humidity with less energy.

Zoning

Dampers and multiple thermostats that let one system heat or cool parts of the house independently.

From the Pros.

Written by the people who do this work every day, in your area.

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