HVAC Glossary and Definitions

Glossary of technical terms every home owner should know.


Annual Fuel Utilization Efficiency. Indicated as a percentage, AFUE tells you how much energy is being converted to heat. For example, an AFUE of 90 means that 90% of the fuel is being used to warm your home while the other 10% escapes as exhaust.

Air Handler

The fan blower, filter and housing parts of a system.


British Thermal Unit. One BTU is equal to the heat given off by a wooden kitchen match. For heating systems, BTU is a measure of the heat given off when fuel is combusted. For cooling system, it is a measure of the heat extracted from your home.


BTUs per hour.


The ability of a heating or cooling system to heat or cool a given amount of space. For heating, this is usually expressed in BTUs. For cooling, it is usually expressed in tons.


Cubic Feet per Minute. A measurement of airflow that indicates how many cubic feet of air pass by a stationary point in one minute.


Part of a split-system heat pump or air conditioner's outdoor unit that controls the pressure applied to the refrigerant. The compressor is necessary for taking in heat to warm your home or getting rid of heat to keep your home cool.

Condenser Coil

Part of the outdoor portion of a split-system heat pump or air conditioner. By converting refrigerant that is in a gas form back to a liquid, the coil sends heat carried by the refrigerant to the outside.


A type of valve used in ductwork that opens or closes to control airflow. These are used to control the amount of warm or cool air entering certain areas of your home.

Direct Vent

A heating system that pulls outside air for combustion and vents combustion gases directly outside.


A type of furnace that takes cool air from the top and blows warm air to the bottom. This is common when the furnace is located in a second-floor closet or utility area.


Electronically Commulated Motor. An ECM is an ultra high efficiency programmable brushless DC motor that utilizes a permanent magnet rotor and a built-in inverter. They are significantly more energy efficient than traditional AC motors and are also much easier to control.

Electronic Air Cleaner

A device that filters out large particles and contaminants in indoor air then electronically pulls out tiny particles that have been magnetized, such as viruses and bacteria, drawing them to a collector plate.

Energy Load Analysis

A series of studies performed to estimate the heating or cooling requirements of your home. It uses information such as the square footage of your home, window and door areas, insulation quality and local climate to determine the heating and cooling capacity needed by your furnace, heat pump or air conditioner. Also known as a Heat Loss Analysis.

Evaporator Coil

Part of the indoor portion a split-system heat pump or air conditioner located indoors. The evaporator coil cools and dehumidifies the air by converting liquid refrigerant into a gas, which absorbs the heat from the air. The warmed refrigerant is then carried through a tube to the outdoor unit.

Heat Exchanger

The part of a furnace that transfers heat to nearby air.

Heat Loss Analysis

See Energy Load Analysis.

High-Efficiency Furnace

Also known as a condensing furnace, a high-efficiency furnace provides your home with ideal heating comfort while using less energy than other models. High-efficiency furnaces are designed to extract additional heat from natural gas, condensing the flue gases in the process.

Horizontal Flow

A type of furnace that draws in air from one side, heats it and then sends the warm air out the other side. Most often used for installations in attics or crawl spaces.


A piece of equipment that adds water vapor to heated air as it moves out of the furnace. This adds necessary moisture to protect furnishings and reduce static electricity.


Heating, Ventilation and Air Conditioning.

Matched System

A heating and cooling system comprised of products that have been certified to perform at promised comfort and efficiency levels when specifically used together.

Mid-Efficiency Furnace

Mid-efficiency gas furnaces use a naturally aspirating burner and do not have a continuously lit pilot light. They are equipped with a powered exhaust and do not have a draft hood. Seasonal efficiency is much higher than conventional furnaces.


A multi-poise furnace is capable of operating in both vertical and horizontal flow orientations.

Payback Analysis

Overall measure of the efficiency and value of your heating and air conditioning system. By combining your purchase price and ongoing operating costs, a payback analysis determines the number of years required before monthly energy savings offset the purchase price.


Puron R410A refrigerant is an environmentally-sound refrigerant designed not to harm the ozone layer and has been approved as a replacement for older Freon R22 refrigerant. All manufacturers will be required to phase out the production of units using R22 refrigerant by 2010, and the complete phase out of R22 refrigerant will occur by 2030.


Returning used refrigerant to the manufacturer for disposal or recycling.

Reciprocating Compressor

A type of compressor used in air conditioners that compresses refrigerant by using a piston-like action.


The substance used in a refrigerating mechanism. It absorbs heat by changing from a liquid to a gas then releases this heat in a condenser as the substance returns from a gas back to a liquid.


Seasonal Energy Efficiency Ratio. This is a measure of the cooling efficiency of your central air conditioner or heat pump. The higher the SEER number, the more efficient the system is at converting electricity into cooling power.

Scroll Compressor

A specially designed compressor that works in a circular motion to compress refrigerant.

Setback Thermostat

A state-of-the-art electronic thermostat with built-in memory that can be programmed for different temperature settings at different times of the day.

Split System

Refers to an air conditioner or heat pump that has components in two locations, usually with one part of the system located inside and the other outside your home.


A unit that monitors and controls your HVAC system.


A unit of measure for cooling capacity. One ton is equal 12,000 BTUH.


A type of furnace that draws cool air from the bottom and blows the warmed air out the top into the ductwork. This type of furnace is usually installed in a basement or an out-of-the-way closet.


A ventilator captures heating or cooling energy from stale indoor air and transfers it to fresh incoming air.


A way to increase your home comfort and energy efficiency by controlling when and where heating and cooling occurs in a home. Programmable thermostats are used to control operating times of the equipment while dampers are used to direct air flow to certain parts of the home.