Glossary of Terms

Find definitions for the most commonly used terms in the business.

AFUE (Annual Fuel Utilization Efficiency) – Used to measure a furnace’s heating efficiency, AFUE is a ratio of the usable heat put off by a furnace compared to the amount of energy consumed in the process. The higher the AFUE, the less heat and fuel a furnace will waste during daily operation, and the less it will cost per season to use.

Air Handler – The indoor component of a split system that connects to the building’s ductwork to distribute cooled or heated air.

AHRI (Air-Conditioning, Heating, and Refrigeration Institute) – Develops industry standards for air conditioning, heating, and commercial refrigeration equipment. The full line of Allied Commercial products is AHRI-certified, so you know you’re getting dependable quality and performance in every unit.

AOH (Annual Operating Hours) – An estimate of how many hours a heating or cooling unit will operate each year, based on typical weather conditions in the geographical area.

Btu (British thermal unit) – A traditional measure of energy used in the heating industry. The higher the Btu, the greater the heating capacity of the unit.

CFM (Cubic feet per minute) – Indicates how much air flows into a space per minute. A larger space will require an HVAC system with a higher CFM to properly heat or cool the air.

Compressor – A component of each air conditioner and heat pump that pressurizes refrigerant gas in order for it to cool the indoor air.

Condenser Coil – A component of each air conditioner and heat pump that absorbs the excess heat generated by the cooling process.

Damper – An adjustable plate located in the ductwork that helps control the flow of air throughout the building. A zoning system may utilize multiple dampers, each connected to a zone-specific thermostat, to regulate the airflow in each zone.

dB (Decibel) – A unit used to indicate the intensity of sound. The lower the decibel rating, the quieter the operation of the unit.

DOE (Department of Energy) – An agency of the U.S. government that sets efficiency standards for HVAC equipment.

Downflow – When a furnace or air handler circulates air from the top to the bottom of the unit. Downflow units are most often used in attic or main floor installations.

Dry-charged Unit – In replacement situations, an air conditioner or heat pump that is shipped without refrigerant (“dry”) and then charged at the installation sites.

ENERGY STAR® – Designates a heating or cooling unit that meets or exceeds efficiency standards set by the EPA.

EPA (Environmental Protection Agency) – A federal agency that develops and enforces U.S. environmental regulations, in addition to overseeing the ENERGY STAR® program.

Evaporator Coil – A low-pressure component of every air handler that contains heat-absorbing refrigerant.

Fan Coil – Typically used in nonducted installations, a fan coil unit includes a fan and cooling or heating coil.

Heat Exchanger – The part of each furnace that transfers heat to the surrounding air, which is then distributed throughout the building.

Heat Pump – Ideal for milder climates, a heat pump is an outdoor unit that can provide efficient heating and cooling. On colder days, the unit draws heat from outdoor air and circulates it indoors. In warmer seasons, the process reverses and the unit removes heat from indoor air and releases it outdoors.

Horizontal Flow – When a furnace or air handler circulates air from one side to the other, typically in attic or crawlspace installations.

HSPF (Heating Season Performance Factor) – Used to measure the efficiency of heat pumps, HSPF is the ratio between heat energy supplied to a building during a typical heating season compared to the amount of electricity consumed. The higher the HSPF, the less electricity is needed to deliver a set amount of heat.

IEER (Integrated Energy Efficiency Ratio) – Used to indicate the part-load efficiency of commercial air conditioning equipment based on weighted operation at various load capacities.

Indoor Coil – See Evaporator Coil.

ISO 9001 – Widely used quality assurance standards developed by the International Organization for Standardization. All Allied Commercial products are ISO 9001 certified to ensure lasting, reliable performance.

LEED (Leadership in Energy and Environmental Design)  A system of ratings created as guidelines for the construction, design and daily operation of environmentally friendly “green” buildings.

Outdoor Coil – See Condenser Coil.

Packaged System – Combines heating and cooling systems in one outdoor unit, typically installed on a building’s rooftop or on a concrete slab close to the building. Common in commercial applications.

R410A Refrigerant – An environmentally friendly, chlorine-free refrigerant that meets the latest guidelines set by the EPA.

Refrigerant – A chemical that produces a cooling effect while expanding or vaporizing.

Refrigerant Lines – Two copper lines that connect the outdoor air conditioner or heat pump to the indoor evaporator coil.

Scroll Compressor – Part of an air conditioner or heat pump that compresses refrigerant in a circular motion (as opposed to up-and-down piston action) for quiet, efficient and more reliable operation.

SEER (Seasonal Energy Efficiency Ratio) – Used to rate the energy efficiency of air conditioners, SEER is the ratio between the amount of cooling output a unit produces during a typical cooling season divided by the total amount of electricity it consumes while doing so. The higher the SEER, the more cooling is produced per watt hour of electricity, and the lower HVAC costs become during the summer.

Split System – An HVAC system in which some components are located indoors, such as the furnace, and some are located outdoors, such as the air conditioner. More common to residential and replacement applications.

Two-Stage Operation – Offers two levels of heating and cooling performance to deliver greater efficiency and temperature control.

Upflow – When a furnace or air handler circulates air from the bottom to the top of the unit. Upflow units are most often used in basement or crawlspace installations.

USGBC (U.S. Green Building Council) – A nonprofit organization that developed the LEED building rating system and promotes sustainable building design and construction in the U.S.

Variable Speed Motor – Automatically adjusts heating and cooling output in response to changing weather conditions to deliver greater efficiency and temperature control than single-stage motors.

Zoning System – Creates separate temperature zones throughout the building to provide enhanced temperature control and energy efficiency. Dampers located in the ductwork help direct airflow to each zone, which is connected to its own programmable thermostat.