HVAC Glossary

Common Residential HVAC System Terms and Definitions

Heating, ventilation and air conditioning (HVAC) terminology can be confusing – and for good reason. With a variety of acronyms and an abundance of industry-specific language, it can feel overwhelming. But this guide to common residential HVAC terms will help you understand what many of those numbers and phrases actually mean.

Residential HVAC System Equipment

Air Handler

The portion of a central air conditioning or heat pump system that moves heated or cooled air throughout a home's ductwork. In some systems, a furnace handles this function.

Condensing/Outdoor Unit

The portion of a central air conditioning system located outside the home. It functions as a heat transfer point for collecting heat from, and dispelling heat to, the outside air.

Heat Pump

An air conditioner that contains a valve which allows for alternation between heating and cooling.

Single Package

A year-round heating and air conditioning system with all components encased in one unit outside the home.

Split System

A heat pump or central air conditioning system with components located both inside and outside the home. The most common design for home use.

Unit Components

Compressor

The pump that moves refrigerant from the indoor evaporator coil to the outdoor condensing unit and back to the evaporator. The compressor functions as the heart of the system as it circulates refrigerant in a loop.

Condenser Coil

A network of refrigerant-filled tubes where heat leaves hot refrigerant vapor. This vapor then condenses into a liquid capable of absorbing more heat.

Evaporator Coil

The portion of the heat pump or central air conditioning system located in the home. It functions as the heat transfer point for warming or cooling air.

Efficiency Ratings/Measurement

AFUE %

Annual fuel utilization efficiency. A measure of a furnace's heating efficiency. The higher the AFUE, the more efficient the product. Currently, the government's established minimum AFUE rating for non-weatherized gas furnaces vented through a chimney is 81% AFUE.

BTU

British thermal unit. The amount of heat required to raise the temperature of one pound of water (or about one pint) by one degree Fahrenheit.

HSPF

Heating seasonal performance factor. A measure of a heat pump's heating efficiency. The higher the HSPF, the more efficient the product. Unlike furnaces with AFUE, there isn't a government established minimum HSPF rating for heat pumps.

MERV

Minimum efficiency reporting value. A measure of air filter efficiency. Higher ratings mean a filter is more efficient in capturing particles in the air.

SEER

Seasonal energy efficiency ratio. A measure of an air conditioner's cooling efficiency. SEER levels may be as low as 13, 14, 15, or 16 with higher performing models obtaining SEER levels of 17, 18, 19, 20 or higher. For example, a product with a 21 SEER rating would be an extremely efficient product.

Ton

A ton is the cooling capacity of an air conditioning system. It's equal to the amount of heat required to melt one ton of ice over 24 hours. For instance, a one-ton air conditioner would be rated at 12,000 BTU per hour (BTUh).

Other Common HVAC Terms

ASHRAE

The American Society of Heating, Refrigerating and Air-Conditioning Engineers is a not-for-profit trade organization founded in 1894. Its stated goals include the advancement of heating, ventilation, air conditioning and refrigeration system design and construction.

Balance Point

An outdoor temperature, usually between 30° F and 45° F, at which a heat pump's output equals exactly the heating needs of the home. Below this point, supplementary electric resistance heat is needed to maintain indoor comfort.

Heat Source

A body of air or liquid from which heat is collected. For example, YORK® Heat Pumps use air from outside the home as the heat source during the heating cycle.

Load Calculation

Completed by an HVAC professional, load calculation helps determine the system size necessary for a home (heating or cooling), based on how much heat is gained or lost.

Supplementary Heat

Auxiliary or emergency heat, usually electrical resistance heat, provided when temperatures are below a heat pump's balance point.

Variable Speed

Refers to a motor that operates at different speeds to more accurately control the flow of heated or cooled air around the home.

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