Buyer’s Guide

Glossary of Terms

Knowing the terms and technical definitions for heating and cooling equipment helps make your planning easier. We hope you find this page useful when deciding the best product for your home’s needs.

General Knowledge

Constant Torque Motor
A furnace with a constant torque motor can provide lower operating costs and increase overall system performance.
This stands for Heating, Ventilating and Air Conditioning and are the initials often used to describe the industry that produces the equipment that brings comfort to your home.
Two-Stage Operation
Rather than being “all on” or “all off,” two-stage units can adjust their output based on the conditions inside or outside your home.
Variable Speed Motor
A furnace with a variable speed motor can adjust humidity levels and create more even temperatures throughout your home.


Annual Fuel Utilization Efficiency is a percentage measurement of a furnace’s heating efficiency. The U.S. government’s minimum efficiency level is 78%, while the Canadian minimum is 90%. The higher the AFUE, the more efficient the furnace.
Products that have the ENERGY STAR® label prevent greenhouse gas emissions by meeting strict energy efficiency guidelines set by the U.S. Environmental Protection Agency and the U.S. Department of Energy. To learn more, please visit
Heating Seasonal Performance Factor is a measurement of a heat pump’s heating efficiency. The higher the HSPF, the more efficient the heat pump’s heating performance.
Seasonal Energy Efficiency Ratio is a measurement of the efficiency of cooling products. The higher the SEER, the more efficient the cooling product.
A Note About Efficiencies:

When you’re getting ready to replace an older heating or cooling system, it’s very important for you to get a load calculation done by your dealer. The greater the difference between the efficiency of your old system and the new system, the more likelihood that the dealer will recommend a smaller-sized unit. This should not cause alarm, as the dealer, by performing a load calculation, will be able to accurately size the system to the demand in your home. It can be quite detrimental to equipment if the units are too large for the load in your home: they can start to “short cycle” (they run often but for very short periods of time, because they are pumping out too much heat/cooling and reach the thermostat’s setting too quickly), which can shorten the life of the unit dramatically.


Ambient Temperature
This is the air temperature (usually the outdoor air temperature) surrounding the equipment.
British Thermal Unit is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. You’ll see this measurement when you look at heating and cooling capacities; for example, your dealer may recommend a 75,000 Btu furnace and a 24,000 Btu air conditioner for your home.
A Note About Capacities:

Gas furnaces are generally rated by in BTUs per hour (btuh). A furnace rated at 100,000 Btuh and 80% AFUE (80% efficient) will have an output of 80,000 Btuh. In other words, 80% of the total heat produced by burning the gas will be in the form of usable heat to warm your home. The other 20% is exhausted from your house along with the flue products.

By the same token, a 100,000 Btuh furnace that is 90% efficient only sends 10% of the total heat out the chimney, thus burning less gas to get the same results and reducing your gas heating costs.

Coefficient Of Performance is a ratio that compares a heat pump system’s heating efficiency to that of electric resistance heat. For example, a heat pump system with a COP of 3.0 provides heat at 3 times the efficiency of electric resistance heat. A heat pump’s system COP will decrease as outdoor temperatures drop, eventually providing little or no efficiency advantage over electric resistance heat, and that’s when auxiliary heat strips start to heat your home.
Gallons Per Hour. You might see this rating if you are looking at an oil furnace. In addition to input and output, an oil furnace also has a rating of gallons per hour, the volume of oil a furnace is capable of burning in 60 minutes.
A Note About Oil Furnaces:

Many oil furnaces are dual-rated. That is, they are listed with two different heating capacities. For example, your oil furnace might be rated as:

Lower capacity: Output = 113,000 Btuh/.85 gph
Higher capacity: Output = 125,000 Btuh/1.00 gph

This means that at the lower rating, the furnace is capable of producing 113,000 Btus of usable heat per hour to heat your home. And, if it ran constantly for one hour, it would consume .85 gallons of oil. If, however, your dealer sets up your oil furnace to operate at the higher rating, it would produce 125,000 Btus of usable heat per hour, and use 1.00 gallons of oil. Whether your oil furnace is set up by your dealer to operate at the higher or lower rating depends on the load calculation. By properly sizing the furnace to your home, you will be assured of maximum comfort, energy savings and extended equipment life.

This is a measurement of the capacity of an air conditioning system. Just like gas and oil furnaces, air conditioners and heat pumps are rated in Btus. One ton of air conditioning is 12,000 Btus per hour. This means that a “one ton” air conditioning system has the capability of removing 12,000 Btus of heat per hour from your home.
A Note About Air Conditioning:

Air conditioning systems do more than just cool your home—they also remove moisture. The more humid it is outside, the harder an air conditioner has to work. But that doesn’t mean a bigger unit will work better. An air conditioning system that is too large will neither cool nor dehumidify properly, and the result will be an uncomfortable, clammy home.