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Glossary of Useful Terms

AFUE - Annual Fuel Utilization Efficiency

This is the rating that all heating systems are given by the federal government, and rates the efficiency of each manufacturers system. It is similar to the EPA ratings for gas mileage on your car. The higher the AFUE rating, the higher the efficiency, and therefore, the lower your heating bill. Gas systems run as high as 96% and oil as high as 86% AFUE.


A boiler produces hot water to heat a home using hot water baseboard, radiant floor heat, European style panel radiators, or to circulate hot water to hydro-air air handlers.

BTU’s - British Thermal Units

A measurement of heat and cooling used in the heating and cooling business. All equipment is rated in BTU’s. The higher the number, the more heating or cooling you have. One BTU is equal to the heat a single wood match produces when burning.

Condensing Unit

This is the outdoor unit that contains the a/c compressor (just like your refrigerator), that produces the cooling for your central a/c system.


This device, located in the basement, dries out a humid basement in spring, summer and fall. Ideally, it should be installed to allow a hose to drain the moisture into a sump in the basement, precluding daily emptying of the dehumidifier bucket.

ERV - Energy Recovery Ventilator

This device is similar to an HRV except it also recovers the moisture in winter that would ordinarily be lost to the outside. In summer, it brings in fresh air while rejecting the excess moisture to the outside. This allows your central a/c system to work easier by not having to dehumidify the hot humid air being introduced by the ventilator.

Warm Air Furnace

This is a popular system that produces warm air to heat the home. Metal ductwork distributes warm air from the furnace to floor and ceiling registers throughout the house.

Geothermal Heat Pumps

These are used for heating and cooling. They use a series of 400 foot bore holes with HDPE piping containing a mixture of water and non toxic gycol to either reject heat to the earth in summer or extract heat from the earth in the winter.

HEPA - High Efficiency Particulate Filter

This is similar to the air filters that hospitals use, but on a smaller scale for homes. They can be free standing devices in a room, or whole house devices attached to a warm air heating system. This allows all rooms to get the benefit of the filtration it produces.

HRV - Heat Recovery Ventilator

This device, located in attics and basements, brings fresh air in to the home while exhausting the same volume of air, and recovering 75 to 80% of the heat. It is more efficient and comfortable than opening windows in winter.


This is the device that is attached to the basement warm air furnace or hydro-air air handler, and produces moisture for the home in winter. Typically, 30% to 35% relative humidity is comfortable in the winter.

Hydro Air

This is a system whereby a hot water boiler produces hot water, and pumps it into a special air handler with both heating and cooling coils inside (they look like car radiators inside the air handlers). It looks like the indoor air handler of a central a/c system and produces both warm air from hot water to heat the home in winter and cooling in summer.

Media Filters

These are used on all warm air heating and central cooling systems to filter the air to a high level. They are ideal for families with allergies.

Registers, Grilles and Diffusers

These are the “grilles” on your floor, walls and ceilings that bring warm or cool air into each room.

SEER - Seasonal Energy Efficiency Ratio

This is the ratio of electricity consumed by the a/c or heat pump system compared to the energy it produces. The federal government rates the equipment. The higher the SEER number, the more energy efficient the system is.


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