A Helpful HVAC Glossary

HVAC services

When it comes to HVAC services, our experts are always talking in industry terms. However, we know you may not be familiar with what “HSPF” stands for or what a programmable thermostat does, so we’ve created a basic HVAC glossary to help. If you have a term that isn’t defined in this article, feel free to “ask the expert.”


Annualized Fuel Utilization Efficiency, which is a way to measure heating efficiency. The higher the AFUE number on your HVAC unit, the more efficient the heating.


The motion of air currents; usually referring to how well air can travel in your home.


British Thermal Unit, which measures the amount of heat produced in relation to fuel consumed.

Central Air

A type of HVAC unit that produces warm or cold air at a central location, then distributes it throughout your home using ducts.


Found in an outdoor air conditioner or heat pump, the compressor is responsible for pumping refrigerant.

Condenser Coil

Found in an outdoor air conditioner or heat pump, the condenser coil is responsible for producing or collecting heat (depending on the temperature outside).


A movable plate that regulates airflow in the ductwork; usually used in zoning applications.


The Department of Energy, which is a federal agency that regulates efficiency standards and supervises energy consumption.

Dual Fuel

A system that produces heat from a combination of sources. For example, a home with an electric heat pump and backup heat source that burns either natural gas, oil, or propane is a dual fuel system.


The channel of vents that carries warm or cold air through your home.

Evaporator Coil

Found in an air conditioner or heat pump, the evaporator coil is responsible for absorbing the heat in your home.


The part of an HVAC system that adds heat to air before it’s distributed throughout your home.

Geothermal Energy

The layer of Earth below the surface maintains a constant temperature that is warmer than the average surface temperatures in winter and cooler in summer. Geothermal HVAC units use specialized coils (or loops) that extend into this layer of the Earth to transfer heat and balance temperature in your home.

Heat Exchanger

Found in a furnace, the heat exchanger is responsible for making the air inside warm before it’s distributed throughout your home.

Heat Pump

A type of HVAC unit, a heat pump moves heat (either by removing it from your home or pumping it into your home) in order to heat or cool the area.


Heating Seasonal Performance Factor, which is used to measure the heating efficiency of heat pumps. The higher the number, the more efficient the heating.


A system that adds moisture to air to improve breathing, help prevent illnesses, reduce asthma symptoms, and more.


Heating, Ventilation, and Air Conditioning.

MERV Rating

Minimum Efficiency Reporting Value, which is used to measure the efficiency of air filters. The higher the number, the more efficient the filter is at trapping airborne particles.

Programmable Thermostat

A thermostat that can automatically adjust the temperature throughout the day based on programmed settings.


A fluid that produces a cooling effect as it transforms from a liquid to a gas and back.

Refrigerant Lines

Found in an air conditioner or heat pump, refrigerant lines are copper lines that connect the outdoor unit to the indoor evaporator coil.


Seasonal Energy Efficiency Ratio, which is used to measure the energy efficiency of air conditioners. The higher the number, the more efficient the air conditioner is.


A system that lets you control the output of heat or air conditioning from your equipment in order to keep your home comfortable.


A unit used to measure the cooling capacity of air conditioners. A 3, 4, or 5-ton unit doesn’t refer to the weight of the unit, but the amount of heat the air conditioner can remove from the home in one hour.

Bonus: Why tons? Because before air conditioning, people cooled their homes with ice that had been harvested from lakes and rivers in the winter. There’s a complicated mathematical formula involved in converting the weight of that ice into energy, but in the end a “ton” of air conditioning capacity represents 12,000 BTU per hour. So a 2-ton unit has 24,000 BTU/hr and a 3-ton 36,000 BTU/hr, and so on.


An application for homes or buildings that allows for independent comfort control of specific areas using a system of thermostats and dampers that direct the flow of heated or cooled air from a central system. For more information about zoning, read our blog, “The Benefits of an HVAC Zoning System.”