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What is HVAC?

The Answer Guide

What Does HVAC Stand For?

Does an air conditioner really weigh 3 tons?...

Like many industries, the heating and air conditioning industry has its own set of terminology and jargon. Technicians and salespeople use these terms when they talk with you. Manufacturer literature uses these terms. No one explains them.

In this Answer Guide, we offer a brief explanation of some of the most common jargon.

Major Components

Condensing unit: Air conditioning equipment that typically sits outside a house, containing a condenser coil and compressor. The compressor raises the pressure of refrigerant vapor and the condenser coil converts the refrigerant vapor to liquid.

Metering device: An expansion valve or orifice that meters liquid refrigerant into an evaporator coil.

Evaporator: The indoor coil of an air conditioner where liquid refrigerant evaporates, drawing heat from the surrounding air, “cooling” the air. In a “packaged” system, all components are located in a single, outside unit.

Blower: A central fan that pushes heated air from a furnace down the duct system or air across an air conditioner’s evaporator coil and down the duct system.

Duct System: Enclosed conduit for distributing air through a house.

Heat Pump: An air conditioner with a “reversing valve” that allows it to operate in reverse, pumping heat from a house to the outside.


HVAC: Heating, Ventilating, and Air Conditioning, a short cut description of the comfort industry.

Btu: British thermal unit, a measure of energy equal to the amount of heat required to raise one pound of water by 1ºF. A Btu is approximately the same as the energy contained in a burning match stick. A Btuh is the number of Btus used in one hour.

Ton: A measure of energy equal to the amount of heat required to melt one ton of ice in a 24 hour period. 12,000 Btus = 1 ton.

SEER: Seasonal Energy Efficiency Ratio, a measure of an air conditioner’s efficiency over the entire cooling season. A higher SEER denotes higher efficiency. The current minimum is 10, which was considered “high efficiency” a few years ago.

HSPF: Heating Season Performance Factor, a measure of a heat pump’s heating efficiency that’s similar to SEER. A higher HSPF denotes higher efficiency. The current minimum is 6.8.

COP: Coefficient of Performance, another measure of heat pump heating efficiency. A higher COP denotes higher efficiency.

AFUE: Annual Fuel Utilization Efficiency, a measure of heating efficiency. A higher AFUE denotes higher efficiency. The current minimum is 78%.

Bels: A measure of sound used for rating air conditioners. 10 decibels = 1 bel. Fewer bels means quieter operation. The scale is logarithmic like the Richter Scale, so an increase of 0.3 bels doubles the sound.

Load Calculation: A calculation process for determining the amount of heating and air conditioning required to heat or cool a house. Most load calculations are based on “Manual J” from the Air Conditioning Contractors of America.

NATE: North American Technician Excellence, the professional certification body for heating and air conditioning technicians.

ARI: Air-conditioning & Refrigeration Institute, an association of equipment manufacturers that publishes industry rating standards.

© 2003 Service Roundtable