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    HVAC Dictionary

    The HVAC industry can be a maze of unfamiliar acronyms and industry terms. This dictionary will help you navigate the most common terms you’ll come across in residential Heating and Cooling.

    A B C D E F G H I K L M N O P R S T U V W Z


    AC Alternating Current - A type of current where the polarity is perpetually reversing, causing the directional flow in a circuit to reverse at regular intervals.

    ACCA - Air Conditioning Contractors of America.

    A-Coil - A heat exchanger consisting of two diagonal coils that are joined together and looks like the letter "A".

    Acoustical - Relating to sound, the science of sound, or a sense of hearing.

    AFUE - Annual Fuel Utilization Efficiency. A measurement used to rate furnace efficiencies by dividing the ratio of heat output by heat input.

    AGA - American Gas Association, Inc.

    Air Balance Test - A test used to measure airflow across a tower or air handler system.

    Air Balancing Hood - Measures airflow from grilles and diffusers.

    Air Conditioner - A device that changes humidity levels, temperature or quality of air.

    Air Flow Volume - The amount of air the system circulates through your home, expressed in cubic feet per minute (cfm). Proper air flow depends on the outdoor unit, the indoor unit, the ductwork and even whether the filters are clean.

    Air Handler - Parts of a system including the fan-blower, filter and housing. The portion of the 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.

    Amp (Ampere) - The practical meter-kilogram-second unit of electric current that is equivalent to a flow of one coulomb per second or to the steady current produced by one volt applied across a resistance of one ohm.

    ARI - Air Conditioning and Refrigeration Institute.

    ASHRAE - American Society of Heating, Refrigeration and Air Conditioning Engineers.



    Bearing - A support or guide by means of which a moving part such as a shaft or axle is positioned with respect to the other parts of a mechanism.

    Biocide - A substance that is destructive to many different organisms.

    BTU - British Thermal Unit. Used for both heating and cooling, BTU is a measure of the heat given off when fuel is combusted. Or for cooling, it’s a measure of heat extracted from your home. One BTU is equal to the heat given off by a wooden kitchen match. BTU also measures the amount of heat required to raise or lower the temperature of one pound of water 1o Fahrenheit.

    BTUh - British Thermal Units per hour. 12,000 BTUh equals one ton of cooling.

    Burner - The device that facilitates the combustion of air and gas.

    Burner Orifice - The opening in the burner through which the gas or fuel passes prior to combustion.



    Capacity - HVAC capacity is the output produced by the heating or cooling unit and is measured in BTUs per hour. For cooling it is sometimes expressed in "tons."

    Celsius - A temperature scale that registers the freezing point of water as 0° and the boiling point as 100° under normal atmospheric pressure.

    CFM - Cubic Feet per Minute. A measurement of airflow volume.

    Charging a System - Adding coolant, or refrigerant, to an HVAC system.

    Coil Cleaning - The act of removing or cleaning dirt, dust, grime, hair and oils from either an indoor or outdoor evaporator or condenser coil.

    Compressor - A pump that increases the pressure of gas. The motor in the compressor is the main consumer of energy. If the compressor operates out of its original design, it will effect energy consumption.

    Condensate - Vapor that is turned into a liquid as its temperature is lowered.

    Condenser - Also called a condensing unit - Heat exchanger where the system heat is rejected and the refrigerant condenses into a liquid. (This is the equipment most often called the "air Conditioner" usually located on the ground or rooftop outside a home or building.

    Condenser Coil - Also an outdoor coil. A device that removes heat from the refrigerant, allowing the refrigerant to be converted from vapor to liquid.

    Condenser Fan - A fan that passes air over the condenser coil to facilitate the removal of heat from the refrigerant.

    Contactor - A switch that can repeatedly cycle, making and breaking an electrical circuit. When sufficient current flows through the A-coil built into the contactor, the resulting magnetic field causes the contacts to be pulled in or closed.

    CSA - Canadian Standards Association.



    DC - Direct Current. A type of electrical current that only flows in one direction.

    Damper - Found at the exit point of ductwork, this plate usually contains grates that can be opened or closed to control the flow of air into a zone.

    Degree-Day - Calculated by subtracting the average outdoor temperature for an area from 65º Fahrenheit. This measurement is used to estimate the amount of heating or cooling a home or building will need.

    Dehumidifier - A device that removes humidity, or moisture, from the air.

    Diffuser - A grille over an air supply duct with vanes that distribute the discharging air in a specific pattern or direction.

    DOE - Department of Energy.

    Downflow Furnace - A furnace with an intake on the top and an air discharge at the bottom.

    Drain Pan - Also a condensate pan. As the refrigerant vapor is liquefied, the drain pan collects the condensate and funnels it to the drain line.

    Dry Bulb Temperature - The temperature as measured without the consideration of humidity.

    Ductwork - A network of metal, fiberboard or flexible material flowing throughout a space which delivers air from an HVAC unit to the respective zones of a home or office.



    EER - Energy Efficiency Ratio.

    Electronic Air Cleaner (EAC) - An electronic device that filters out large particles and contaminants in indoor air. It then electronically pulls out tiny particles that have been magnetized, such as viruses and bacteria, drawing them to a collector plate.

    EPA - Environmental Protection Agency.

    Expansion Valve - A valve that meters the levels of refrigerant through a temperature or pressure control.

    Evaporator Coil - Part of a air conditioner or heat pump. The evaporator coil cools and dehumidifies the air by converting liquid refrigerant into a gas, which absorbs the heat from the air. The warmed refrigerant is then carried through a tube to the outdoor unit (condenser coil).



    Fahrenheit - A temperature scale in which water freezes at 32 degrees and boils at 212 degrees at normal atmospheric pressure.

    Fan - A device that creates air flow.

    Fan Coil - An indoor component of a heat pump system, used in place of a furnace, to provide additional heating on cold days when the heat pump does not provide adequate heating.

    Filter - A device that acts like a strainer to remove dirt or undesired particles.

    Flue - A vent that removes the byproducts of combustion from a furnace.

    Furnace - The major component in heating a home. A device that facilitates the combustion of fuel and air to create heat.

    Fuse - A delicate metal strip connecting two parts of an electrical circuit. This strip breaks, or melts, in the event of excess electrical charge, breaking the electrical circuit.



    GAMA - Gas Appliance Manufacturers Association.



    Heat Exchanger - A device through which heat is transferred to a cold area or surface. Located in the furnace, the heat exchanger transfers heat to the surrounding air, which is then pumped throughout the home.

    Heat Gain - The amount of heat added or created in a designated area.

    Heating Coil - A coil that acts as a heat source for a heating system.

    Heat Load - A series of studies performed to determine the heating or cooling requirements of your home. An energy load analysis uses information such as the cubic footage, window and door areas, insulation quality and local climate to determine the heating and cooling capacity needed by your furnace, or air conditioner. When referring to heating, this is also called Heat Loss Analysis, since a home’s heating requirements are determined by the amount of heat lost through the roof, entry ways and walls.

    Heat Loss - The amount of heat subtracted from a designated area.

    Heat Pump - A device used for either the heating or cooling of a space by transferring heat between two reservoirs.

    Heat Transfer - Moving heat from one location to another.

    High Efficiency Air Cleaner - An air filter installed in your central system that collects up to 99% of particles 5 microns or larger. In comparison your standard air filter only picks up about 8% of these same particles.

    Horizontal Flow - A type of furnace, installed on its "side," that draws in air from one side, heats it and sends the warm air out the other side. Most often used for installations in attics or crawl spaces.

    HSPF - Heating Seasonal Performance Factor. This factor rates the efficiency of the heating portion of the heat pump.

    Humidifier - A device that adds humidity, or moisture, to the air.

    Humidistat - The device that measures humidity and turns the humidifier on and off.

    Humidity - Dampness in the air caused by water vapor.

    HVAC - Heating, Ventilation and Air Conditioning.



    Ignition - Elevating the temperature of a substance to the point of causing a combustion reaction.

    Indoor Coil - (evaporator coil), part of a split-system air conditioner or heat pump located indoors. The evaporator coil cools and dehumidifies the air by converting liquid refrigerant into a gas, which absorbs the heat from the air. The warmed refrigerant is then carried through a tube to the outdoor unit (condenser coil).



    Kilowatt (kW) - 1,000 watts.



    Latent Heat - A type of heat that when added to an area produces an effect other than an increase in temperature.

    Load Estimate - Also heat load. A series of studies performed to determine the heating or cooling requirements of your home. An energy load analysis uses information such as the square footage, window and door areas, insulation quality and local climate to determine the heating and cooling capacity needed by your furnace, or air conditioner. When referring to heating, this is also called Heat Loss Analysis, since a home’s heating requirements are determined by the amount of heat lost through the roof, entry ways and walls.



    Matched System - A heating and cooling system comprised of products that have been certified to perform at promised comfort and efficiency levels when used together, and used according to design and engineering specifications.

    Media - The fine material of a filter that traps dirt, dust, mildew or bacteria.



    NEC - National Energy Council / National Electric Code.

    NEMA - National Electrical Manufacturing Association.



    Operating Cost - The day-to-day cost to run your home comfort system, based on the energy required to run it.

    Orifice - An opening or hole.

    Outdoor Coil/Condensing Unit - The portion of a heat pump or central air conditioning system that is located outside the home and functions as a heat transfer point for collecting heat from and dispelling heat to the outside air.



    Package Unit - A heating and cooling system contained in one outdoor unit.

    Payback Analysis - Overall measure of the efficiency and value of your home comfort system. By combining your purchase price and ongoing operating costs, a payback analysis determines the number of years required before monthly energy savings offset the purchase price.

    Programmable Thermostat - An electronic thermostat with a built in memory that can be programmed for the different temperature settings at different times of day.

    PSI - Pounds per square inch.

    PSIA - Pounds per square inch, absolute.

    PSIG - Pounds per square inch gauge.

    Puron™ Refrigerant - Puron is a trade marked name for R-410A, an environmentally sound refrigerant designed to protect the earth's ozone layer. Federal law requires all manufacturers phase out ozone depleting refrigerants in the next few years. Puron is approved by the US Environmental Protection Agency as a replacement from Freon 22*.

    PVC - Polyvinyl chloride; a type of plastic.



    R-22 - Chlorodifluoromethane or difluoromonochloromethane is a refrigerant commonly used in air conditioning applications, such as residential split systems in the US, rooftop units and window air conditioners.

    R-410A - Sometimes sold under the trademarked names Puron, Genetron R410A, and AZ-20, is a near-azeotropic mixture of difluoromethane and pentafluoroethane which is used as a refrigerant in air conditioning applications. Unlike many haloalkane refrigerants it does not contribute to ozone depletion, and is therefore becoming more widely used as ozone-depleting refrigerants like R-22 are phased out.

    Reciprocating Compressor - A type of compressor used in cooling systems to compress refrigerant by using a piston action.

    Refrigerant - A chemical that condenses from a vapor to liquid and, in the process, decreases in temperature.

    Refrigerant Charge - The amount of refrigerant in a system.



    SEER - Seasonal Energy Efficiency Ratio. A rating system developed by the U.S. Government to indicate the efficiency level of cooling equipment.

    Self-contained System - A package unit.

    Sensible Heat - Heat added or subtracted that causes a change in temperature.

    Sensor - A device that reacts to a change in conditions.

    Split System - An outdoor unit combined with an indoor unit.



    Thermostat - Sensors that monitor and control the output of an HVAC system.

    Thermostatic Expansion Valve - A device that creates a constant evaporator temperature.

    Ton - One ton is 12,000 BTUs per hour.



    Upflow Furnace - A furnace that pulls in air from the bottom and releases it through the top.



    Vacuum - A space where the pressure is significantly below that of standard atmospheric pressure.

    Variable Speed  - A "smart" motor that runs on DC current and can vary it's operating speed using less electricity and providing increased comfort.

    Volt - A unit of electro-motive force.

    Voltage - The force pushing electrical current along wires and cables.



    Watt - The unit of electrical power equal to the flow of one amp at a potential difference of one volt.

    Wet Bulb Thermometer - A thermometer that measures the relative humidity in the air.



    Zoning - A system that divides a home, office or space into different regions in order to better control the temperature and effectiveness of a heating and cooling system.



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