HVAC Terminology 101

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Once upon a time, home environments were regulated using little more than a furnace and fans. Times have changed immensely in the past few decades, and now HVAC (Heating, Ventilation, and Air Conditioning) is a complicated profession covering a wide variety of options and technologies.

Whether you are planning to upgrade your HVAC system or merely wish to understand the one you have, the following glossary of terms should help. Entries are broken down alphabetically and by category for easier searching.

Cooling-Specific Components

Air Conditioner: component of an HVAC system which uses refrigerants to cool and transfer air.

Compressor: device which compresses and pumps refrigerant from an outdoor air conditioner or heat pump and pumps it into your home.

Condenser Coil: outdoor portion of an air conditioner or heat pump which can release or absorb heat depending on the time of year.

Evaporator Coil: component inside the air handler or attached to your furnace which absorbs heat from the air in your home.

Refrigerant Lines: two copper pipes running between an indoor evaporator coil and external air conditioner or heat pump.

Heating-Specific Components

Air Handler: indoor component which moves warmed or cooled air through the ductwork.

Ductwork: passageways through which air channeled from the furnace or blower coil flow throughout your home.

Furnace: component of an HVAC system where the air is heated and transferred; may run from one of several different fuels.

Heat Exchanger: component inside a furnace which transfers heat to the surrounding area, which in turn is pumped throughout your home.

Humidifier: device which adds moisture to the heated air as it leaves the furnace.

HVAC Components

Blower: device inside an air handler or furnace consisting of a motor and wheel which moves air through your HVAC system.

Damper: movable plate in the ductwork which can be adjusted to redirect or regulate airflow; most commonly found in zoning systems.

Electronic Air Cleaner: device which filters bioaerosols and large particles from indoor air.

Heat Pump: device which takes the place of traditional furnaces and air conditioners by exchanging warm and cool air between the inside and outside of your home, depending upon your temperature settings.

Humidistat: automatic device which maintains a set level of humidity.

Programmable Thermostat: electronic thermostat which may be programmed to activate multiple temperature settings for your HVAC system throughout the day.

Scroll Compressor: specially designed compressor which has circular movement instead of piston-like.

Sequencer: relay which opens circuits in a timed sequence; often found in electric heating units.

Solenoid Valve: valve designed to stop the flow of fluids or refrigerant gasses.

Thermidistat – similar to a thermostat, but measures humidity instead of temperature.

Thermostat: temperature control device containing sensors which detect changes in temperature and relay commands to the HVAC unit based on your temperature settings; most modern thermostats are digital but older models used mercury or other temperature-sensitive methods.

Variable Speed Motor: fan motor designed to adjust the fan’s speed based on input from the thermostat; is less noisy, increases dehumidification, and more energy-efficient than standard fan motors.

HVAC Terminology

Annualized Fuel Utilization Efficiency (AFUE): incremental measurement of heating system efficiency.

Bioaerosols: microscopic airborne organisms which breed in warm, humid air.

British Thermal Unit (BTU): amount of heat required (or removed, for cooling measurements) in an hour to change one pound of water by one degree.

Cubic Feet per Minute (CFM): airflow measurement denoting how many cubic feet off air passes a stationary point within one minute.

Energy Star®: designation to show that an appliance meets or exceeds the Federal guidelines for energy-efficient performance.

Heating Seasonal Performance Factor (HSPF): incremental rating which reflects the efficiency of a heat pump.

Minimum Efficiency Reporting Value (MERV): rating which measures the size of an air filter’s holes; a higher number equates to smaller holes and higher filtering efficiency.

Micron: one millionth of a meter (1//1000 millimeter).

Particles: substances measuring below 100 microns in diameter; particles measuring less than 2.5 microns can have serious health effects when airborne.

Refrigerant: chemical, such as Freon, which has a cooling effect when expanding or vaporizing.

Seasonal Energy Efficiency Ratio (SEER): measurement scale which gives an increasing efficiency rating for heat pumps or cooling units.

Supply: refers to the air coming from an air handler or furnace to indoor ventilation openings such as grills or air vents.

Ton: unit of measurement; in HVAC, one ton equals 1200 BTUs per hour in cooling capacity.

Vapor: gaseous state of liquids, including refrigerants.

Ventilation: referring to both devices and openings in HVAC systems which allow air to vent from one area to another.

Windings: the electrical coils found in many electrical components, including compressors, contractors, and relays.

Types of HVAC Systems

All-in-One System: any system in which all components are located in a single cabinet; usually located beside or atop your home.

Central Air-Conditioning System: system where air is cooled in a central location and distributed outwards.

Dry-Charged Unit: air conditioner or heat pump which is shipped without refrigerant and filled on-site.

Horizontal Flow: air handler or furnace which is oriented on its side and circulates air from one end to the other; commonly used in crawl spaces or attics.

Packaged Unit: HVAC system contained in a single outdoor unit.

Smart Home: home in which multiple functions, including HVAC, are controlled automatically or by remote.

Split System: HVAC system in which the components are in two different locations; usually an outside air conditioner and inside furnace.

Two-Stage Heating/Cooling: system which runs at a lower, energy-saving speed but may switch to a higher secondary stage as needed.

Upflow: furnace or air handler installed vertically in basements or small spaces which circulates air from the side and out through the top.

Zoning System: any HVAC system capable of creating custom temperature zones throughout your home, allowing for better efficiency and comfort.

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