Customer Resources - A Glossary of HVAC Terms
Confused by the many terms and acronyms surrounding your indoor comfort system? Don't be! This handy glossary of terms will tell you what you need to know when discussing your HVAC system with a professional contractor.

13 SEER
This is the new minimum efficiency standard (effective January 2006) for an air conditioner or heat pump. All new units must now meet this standard. Previously manufactured equipment may be used, sold, and installed. SEER is defined later.

AFUE A central furnace or boiler's efficiency is measured by annual fuel utilization efficiency (AFUE).

AFUE is a measure of how efficient the appliance is in using electricity or fossil fuels (oil or gas) over the course of a typical year. An all-electric furnace or boiler has no flue loss through a chimney. The AFUE rating for an all-electric furnace or boiler is between 95% and 100%. The lower values are for units installed outdoors because they have greater jacket heat loss. However, despite their high efficiency, the higher cost of electricity in most parts of the country makes all-electric furnaces or boilers an uneconomic choice. If you are interested in electric heating, you might consider installing a heat-pump system.

The minimum allowed AFUE rating for a noncondensing fossil-fueled, warm-air furnace is 78%; the minimum rating for a fossil-fueled boiler is 80%; and the minimum rating for a gas-fueled steam boiler is 75%. A condensing furnace or boiler condenses the water vapor produced in the combustion process and uses the heat from this condensation. The AFUE rating for a condensing unit can be much higher (by more than 10 percentage points) than a noncondensing furnace. Although a condensing unit costs more than a noncondensing unit, the condensing unit can save you money in fuel costs over the 15 to 20-year life of the unit.

AIR HANDLING UNIT
Equipment with a heating element and/or cooling coil and other components in a cabinet or casing.

BALANCING or AIR BALANCING
Adjusting an air conditioning system so that the right amount of air is delivered to the right places in your home in order to achieve the right heating or cooling effect.

BTU
British Thermal Unit, the measurement of heating and air conditioning capacity. A BTU is the amount of heat that must be added to one pound of water to raise its temperature one degree Fahrenheit.

CFC
Chlorofluorocarbons, used as a refrigerant in air conditioners and heat pumps, linked to the depletion of the ozone layer.

COIL
A heating or cooling element made of pipe or tubing, usually with plates or fins.

CONDENSER (HEAT EXCHANGER)
The outside unit of a heating or air conditioning system. Here the refrigerant condenses from a gas to a liquid and hot or cold air from the building is released to the outside.

DEHUMIDIFIER
A device that removes excess moisture from the air.

DUCT
Conduits used to carry air. They can be round or rectangular, sheet metal or fiberglass or vinyl tubes. In air conditioning systems they carry air from the home to the air conditioning system or furnace and back to the home.

ERV
Energy Recovery Ventilator, a machine that draws fresh air into the home and exhausts stale air from the home. It uses a process to preheat or pre-cool (depending on the season) to reduce energy costs associated with conditioning the air.

ENERGY STAR®
A government supported branding used to identify energy efficient products. The branding was developed by the US Department of Energy and the US Environmental Protection Agency.

FURNACE
A self-contained heating unit that is designed to deliver heated air to a home.

HEAT EXCHANGER
1. The part of a furnace that transfers heat from burning fuel to the air used to heat your home. Also, from a boiler to water for hydronic heating.
2. A device, such as a condenser or evaporator, in which heat is added or removed in order to heat or cool your home.

HEAT PUMP
A single refrigeration system designed to provide both heating and cooling. Compare to a furnace and an air conditioner, separate units that only heat or cool.

HRV
Heat Recovery Venilator, a machine that brings fresh air into a home through a process that preheats the air so it has less impact on your utility bill.

HSPF
Heating Seasonal Performance Factor, an equipment efficiency rating. As with MPG on a car, the higher the rating the more fuel efficient the equipment is.

HUMIDIFIER
A device that adds moisture to warm air for your home.

HVAC
Heating, ventilating, and air conditioning

INFILTRATION
Air that enters your home through holes, gaps, and cracks, (e.g., plumbing or electrical holes, the heating and air conditioning system, doors, and windows).

IAQ
Indoor air quality

LATENT HEAT
The energy that suspends moisture vapor in the air.

LOAD CALCULATION
A mathematical determination of how much cooling and heating (BTUs) an HVAC system must deliver for occupant safety and comfort. It is based on a variety of factors: square footage, building orientation, number of occupants, size and placement of rooms, number and size of windows and doors, amount of insulation, number of floors, and climate.

MANUAL D®
An ACCA procedure covering the proper design, installation, maintenance, and repair of ductwork.

MANUAL J®
An ACCA procedure covering the method for calculating heating and cooling requirements (load calculation) for single-family detached homes and mobile homes.

MATCHED SYSTEM
An air conditioner or heat pump system composed of equipment that has been certified by ARI to work together to deliver the specified heating and cooling capacity at the stated efficiency rating.

ESA
Energy Savings agreement, which provides regular maintenance of your HVAC system. Most ACCA member contractors offer ESA's, although they may use different names for them, such as Maintenance Inspection Agreement, Planned Service Agreement, Energy Service Plan, etc.

R-22
A refrigerant containing chlorine used in air conditioning systems. The EPA has mandated that R-22 cannot be manufactured after 2010 because it has been linked to the depletion of the ozone layer and global warming. Most commonly referred to by its trademarked name, Freon.

R-410A
The refrigerant that replaces R-22. It does not contain chlorine and is not hazardous to the environment.

REFRIGERANT
A fluid that absorbs heat at low temperatures and rejects heat at higher temperatures.

REFRIGERANT CHARGE (or, “charging the refrigerant”)
The procedure an HVACR technician performs to ensure that the system has enough of the right kind refrigerant for peak operating performance.

RELATIVE HUMIDITY (RH)
The percent of moisture actually in the air compared to the maximum amount of moisture the air can hold at that temperature.

RETURN, RETURN AIR, RETURN SIDE
The path the air takes to get to an air-handling unit or furnace so it can be cooled or heated. It is the “return” path. The return side should be “balanced” with the supply side to ensure proper air flow and comfort.

SEER
Seasonal Energy Efficiency Ratio, an equipment efficiency rating that measures how much energy it takes to cool the air. As with MPG on a car, the higher the number the more efficient the unit.

SENSIBLE HEAT
The temperature of the air. This type of heat is measured with a thermometer.

SPLIT SYSTEM
A two-component heating and cooling (heat pump) or cooling only (air conditioner) system. The condensing unit is installed outside, the air handling unit is installed inside (preferably in conditioned space). Refrigerant lines and wiring connect them together.

SUPPLY or SUPPLY SIDE
The part of an HVAC system that takes (supplies) the conditioned air from the air-handling unit or furnace to your home. The supply side should be “balanced” with the return side to ensure proper air flow and comfort.

ZONES, ZONED SYSTEM, ZONING
A single HVAC system that can meet different heating and cooling needs in different areas (zones). Each zone of a home has its own thermostat with which it can regulate the temperature and humidity in its area. One “zoned air conditioner” could be set for a high temperature in one zone and for a lower temperature in the other zone. Zone systems have two or more zones.

Two-Stage Heating Produces Four-Star Comfort

Ever wish you could just take the chill out of your home's air without being overwhelmed with a full blast of heat from your furnace?

Well, now you can, thanks to a new development in gas furnaces called two-stage heating.

According to experts at the Trane Home Comfort Institute, two-stage heating means the gas furnace can operate at either high or low to provide the correct level of comfort with the most efficiency.

They say you'll feel the benefit of two-stage heating most during those transitional times such as a cool autumn night when you just need a little heat to make your house comfortable.

Rather than hitting you with a full blast of heat, the furnace responds with a pre-heat stage, warming the heat exchangers before circulating air throughout the house. Then, the two-speed blower starts at low speed, quietly and gently warming your home.

When colder temperatures set in, the two-stage gas valve automatically increases the fuel flow and the blower switches to high speed for maximum comfort.

Added Benefits

Increased levels of indoor comfort, however, aren't the only benefits two-stage heating provides. Higher levels of efficiency and the lower operating costs that accompany them are others.

The Trane Home Comfort Institute explains that operating costs go down for two reasons. The first is the elimination of short-cycling, which is the frequent starting and stopping common to many single-stage furnaces. Compare it to the operation of a car, and it's similar to the difference in fuel economy between highway driving and stop-and-go driving.

The second is better utilization of fuel. For example, at the end of the high-speed cycle, after the fuel shuts off, the furnace continues to run a few seconds, using the remaining heat in the exchangers before it shuts off. This helps ensure that you get all the heat you've paid for.

Why should I choose a variable speed furnace for my home?

Were Glad You Asked!!!

There are many reasons for choosing a variable speed furnace, but the main reason is comfort. The term "variable speed" refers to the furnace's fan motor, which moves at different speeds to precisely control the flow of heated and cooled air throughout your home. Better airflow control means a better balance of temperature and humidity.

More Comfort and Efficiency, with less sound
More Comfort.Variable speed home comfort systems precisely regulate airflow to provide better control of temperature, humidity, and air distribution.

More Efficiency. Compared to a conventional single speed furnace, a variable speed furnace performs better and uses about two thirds less electricity. During cooling operation, variable speed technology typically results in an efficiency gain of 1 SEER (Seasonal Energy Efficiency Ratio). The higher the SEER, The lower your utility bills.

Less Sound. A variable speed furnace also ensures quieter operation. A technology that combines variable speed operation with sound-reducing design. The furnace slowly ramps up to speed, so there's no sudden "kick" or blast of air at startup.

Better Indoor Air Quality
Cleaner Air. When the furnace is not heating or cooling and the fan in is constant operation (indicated by the "fan" setting on your thermostat), a variable speed furnace will continue to slowly and inexpensively circulate air throughout your home. This allows your filters to capture more contaminants (because air is constantly passing through them), so you can breathe easier.

Enhanced Humidity Control. When moisture levels are high, there's a higher potential for mold growth and other pollutant problems. Compared to a single-speed furnace, a variable speed furnace is more effective at drawing moisture from the air for improved air quality and comfort.

Calculate Your Energy Savings
The variable speed motor will typically use only about 75 watts of power per hour, compared to a conventional blower that uses about 400 watts. Thus, over the course of one year, you can expect to save money on your electric bill with a variable speed motor.

Use this simple formula to calculate your potential energy savings, based upon your existing power costs per kilowatt-hour:

Example: 2,847 kilowatts* X $.80/kW/h = up to $240.00 in energy savings, based upon your existing power costs per kilowatt-hour:

NOTE: Savings are based on an HVAC system that is always operating either in heating, cooling or "fan" mode.

*Average kilowatts saved per year is calculated by saving 325 watts of power per hour with a variable speed motor using 75 watts per hour, versus conventional blower motors using 400 watts per hour, times 8,760 hours in a year, equals 2,847,000 watts/1000, which equals 2,847 kilowatts.

How it works
For any furnace, providing maximum comfort means achieving the proper amount of airflow. This is true for both heating and cooling operations. Unlike conventional single speed motors, a variable speed motor runs at a wide range of speeds. Using intelligent technology, it continually monitors incoming data from your heating and cooling system, and it automatically makes the adjustments necessary to meet your comfort needs. The motor varies the amount of air circulated, compensating for factors like dirty filters by increasing speed. Put simply, it delivers just the right amount of air necessary to provide the desired level of heating and cooling comfort.