Heating & Air Conditioning Glossary
Activated carbon – grainy, processed carbon used by air filters to trap contaminants in the air before they recirculate through your house.
AFUE (Annual Fuel Utilization Efficiency) – measures the percentage of energy that is converted to heat by your furnace or boiler. Not to be confused with EER or SEER, the measurement used for air conditioners and heat pumps.
Air balancing – the process of adjusting your HVAC system to deliver the proper airflow to each room.
Air handler –component of your HVAC system that moves heated or cooled air from the HVAC system into your ducts. It is composed of the blower fan and heat transfer coil, as well as the housing of those components.
Attic fan – fan mounted on your attic wall that exhausts warm attic air outside.
Attic vent –a mechanical device used to ventilate an attic space, primarily to reduce heat buildup and moisture condensation.
Blower fan –fan that moves air from the return duct over the coil / heat exchanger, then through the supply duct into your home.
BTU (British thermal unit) –amount of heat your heating system can output. More is better!
BTUh – BTUs per hour. 12,000 BTUh = one ton of cooling capacity.
CAE – stands forCombined Annual Efficiency. This is a measure of the amount of heat produced for every dollar of fuel consumed for both home and water heating.
Carbon monoxide –colorless, tasteless, odorless, and extremely toxic gas produced by combustion of carbon based fuels. If your furnace is worn out or not properly maintained,carbon monoxide can leak into your home.
Central air conditioner – air conditioner that cools and dehumidifies air at a central location and delivers it through the house by means of an air handler and a network of ducts.
CFM – stands for cubic feet per minute. This measurement refers to how many cubic feet of air pass by a given point in a minute. The higher the number, the more air is being pushed through your duct system.
Coil –one of the main components of an HVAC system. The coil is made of tubing or pipe and often has fins to allow heat to radiate away.
Condenser coil – a network of tubes that removes heat from the heated gas refrigerant and converts the refrigerant back into liquid form.
Compressor –the outdoor unit on a split system air conditioner. The compressor puts pressure on the refrigerant in the air conditioner so that it can flow through the system.
Condenser –device in an air conditioner or heat pump where the refrigerant condenses from a gas into a liquid when it is depressurized or cooled.
Dampers – devices that change the way air flows through your ducts. Dampers can usually be controlled either manually or automatically and allow you to zone your air conditioning system.
dB – decibel; unit used to measure the relative intensity of a sound.
Dual fuel – comfort system that pairs an electric heat pump with a gas furnace, providing an energy efficient alternative to the conventional furnace/air conditioner combination.
Duct fan – fan that helps blow air through your ducts.
Ducts – round or rectangular tubes, usually made of sheet metal, fiberglass board, or a flexible plastic / wire composite, that carry conditioned air through your home.
ENERGY STAR– EPA designation attached to HVAC products that meet or exceed EPA guidelines for high-efficiency performance above the standard government minimums.
Evaporator coil – indoor tubes filled with refrigerant that remove heat from the air, causing the refrigerant to evaporate into a gas.
Forced air HVAC system – any HVAC system that uses a fan to blow conditioned air through air channels or ducts.
Freon – once a very popular refrigerant, it has been phased out in recent years because of a tendency to harm the environment.
Fuel efficiency – refers to the amount of heat produced by your heating system vs. how much fuel you burn.
Heat Exchanger – device located in the furnace that transfers heat to the surrounding air, which is then pumped throughout the home.
HEPA filters (High Efficiency Particulate Arrestance) –filters. HEPA filters are the most effective air filters available and are commonly found in high-end air cleaners.
Horizontal Flow – when an air handler or furnace is positioned on its side and circulates air in one end and out the other. Ideal for attic or crawl space installations.
Humidifier – indoor air quality device that adds moisture to the air as it passes through the furnace and ductwork to be distributed through your home.
Humidistat – automatic device used to maintain the humidity in your home at a fixed or adjustable set point.
HVAC – stands for Heating, Ventilation and Air Conditioning.
MERV Rating – filter effectiveness rating that describes the size of the holes in the filter that allow air to pass through. The higher the MERV rating, the smaller the holes in the filter and the more effective the filter.
Packaged air conditioner – central air conditioner that has the evaporator, compressor and condenser all in the same unit. Not to be confused with a split system air conditioner.
Plenum – any air compartment connected to a duct or ducts.
R-22 refrigerant – once the standard refrigerant used in residential air conditioners, R-22 is being phased out by the EPA and replaces with R-410a.
R-410a refrigerant – the new standard in residential AC refrigerants, R-410a is a chlorine-free refrigerant that meets the EPA's newest, most stringent environmental guidelines.
Refrigerant– chemical that produces a cooling effect while expanding or vaporizing. Most residential air conditioning units contain the standard R-22 refrigerant (in the process of being phased out) or R-410a. Freon is another common refrigerant.
Return air – “used” air that has been cycled through your house and is returning to your HVAC system to be reconditioned.
Return duct –duct through which return air goes to be cycled back through your HVAC system.
Seasonal energy efficiency ratio (SEER) – a measure of efficiency for air conditioners and heat pumps. Specifically, the average BTUs of cooling delivered for every watt-hour of electricity used.
Split system air conditioner – an air conditioner that houses the evaporator, compressor and condenser in separate units.
Supply duct – duct through which conditioned air flows into your room.
Ton (in AC terms) – one unit of cooling capacity or 12,000 BTU per hour.
Two-stage operation– cooling system that provides two levels of heating or cooling output for greater temperature control, energy efficiency, and improved indoor air quality.
Upflow – when an air handler or furnace is installed in an upright position and circulates air through the side or bottom and out through the top. Typically used in basement, closet, and attic installations.
Variable speed motor – motor that automatically adjusts the flow of warm or cool air.
Zone (in AC terms) –area within your home that is individually heated or cooled. A zone has its own thermostat for individual temperature control.