LIC# TACLB 002637E TACLA 002637R

Common terms and definitions as they pertain to HVAC and refrigeration.

Air Conditioner (A/C, AC)
Air conditioners are appliances used to process of altering the properties of air (primarily temperature and humidity) to more comfortable conditions, typically with the aim of distributing the conditioned air to an occupied space to improve thermal comfort and indoor air quality.

Air Exchange Rate
The rate at which outside air replaces indoor air in a space. Expressed in one of two ways: the number of changes of outside air per unit of time – air changes per hour (ACH); or the rate at which a volume of outside air enters per unit of time – cubic feet per minute (CFM).

Air Handler
A fan-blower, heat transfer coil, and housing parts of a system.

Attic Fan
A fan mounted on an attic wall used to exhaust warm attic air to the outside.

The device in an air conditioner that distributes the filtered air from the return duct over the coil/heat exchanger. This circulated air is cooled/heated and then sent through the supply duct, past dampers, and through supply diffusers to the living/working space.

British Thermal Unit (BTU)
The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit, equal to 252 calories.

Building Envelope
Elements of the building, including all external building materials, windows, and walls, that enclose the internal space.

Carbon Dioxide (CO2)
A colorless, odorless noncombustible gas with the formula CO2 that is present in the atmosphere. It is formed by the combustion of carbon and carbon compounds (such as fossil fuels and biomass), by respiration, which is a slow combustion in animals and plants, and by the gradual oxidation of organic matter in the soil.

Carbon Monoxide (CO)
A colorless, odorless but poisonous combustible gas with the formula CO. Carbon monoxide is produced in the incomplete combustion of carbon and carbon compounds such as fossil fuels (i.e. coal, petroleum) and their products (e.g. liquefied petroleum gas, gasoline), and biomass.

Central Heating System
A system where heat is supplied to areas of a building from a single appliance through a network of ducts or pipes.

CFM Cubic feet per minute
The amount of air, in cubic feet, that flows through a given space in one minute. 1 CFM equals approximately 2 liters per second (l/s).

A device used to compress air for mechanical or electrical power production, and in air conditioners, heat pumps, and refrigerators to pressurize the refrigerant and enabling it to flow through the system.

The device in an air conditioner or heat pump in which the refrigerant condenses from a gas to a liquid when it is depressurized or cooled.

Condenser Coil
The device in an air conditioner or heat pump through which the refrigerant is circulated and releases heat to the surroundings when a fan blows outside air over the coils. This will return the hot vapor that entered the coil into a hot liquid upon exiting the coil.

Cooling Capacity
The quantity of heat that a cooling appliance is capable of removing from a room in one hour.

Controls that vary airflow through an air outlet, inlet, or duct. A damper position may be immovable, manually adjustable or part of an automated control system.

A device for reducing the level of humidity in a room or home.

Diffusers and Grilles
Components of the ventilation system that distribute and return air to promote air circulation in the occupied space. As used in this document, supply air enters a space through a diffuser or vent and return air leaves a space through a grille.

The round or rectangular tube(s), generally constructed of sheet metal, fiberglass board, or a flexible plastic-and-wire composite, located within a wall, floor, and ceiling that distributes heated or cooled air in buildings.

Exhaust Ventilation
Mechanical removal of air from a portion of a building (e.g., piece of equipment, room, or general area).

Filter (air)
A device that removes contaminants, by mechanical filtration, from the fresh air stream before the air enters the living space. Filters can be installed as part of a heating/cooling system through which air flows for the purpose of removing particulates before or after the air enters the mechanical components.

A registered trademark for a cholorfluorocarbon (CFC) gas that is highly stable and that has been historically used as a refrigerant.

Furnace (Residential)
Combustion heating appliance in which heat is captured from the burning of a fuel for distribution, comprised mainly of a combustion chamber and heat exchanger.

Heat Loss
The heat that flows from the building interior, through the building envelope to the outside environment.

Heaters are appliances whose purpose is to generate heat (i.e. warmth) for the building. This can be done via central heating. Such a system contains a boiler, furnace, or heat pump to heat water, steam, or air in a central location such as a furnace room in a home, or a mechanical room in a large building. The heat can be transferred by convection, conduction, or radiation.

Heating Capacity (Also Specific Heat)
The quantity of heat necessary to raise the temperature of a specific mass of a substance by one degree.

Heating Load
The rate of heat flow required to maintain a specific indoor temperature; usually measured in Btu per hour.

High efficiency particulate arrestance (filters).

A device for increasing the humidity in a room or home.

An acronym for heating, ventilation, and air-conditioning system.

An electrically charged atom or group of atoms that has lost or gained electrons; a loss makes the resulting particle positively charged; a gain makes the particle negatively charged.

A device that removes airborne particles from breathable air. Negative ions are produced and give up their negative charge to the particles. These new negative particles are then attracted to the positive particles surrounding them. This accumulation process continues until the particles become heavy enough to fall to the ground.

Natural Ventilation
Movement of outdoor air into a space through intentionally provided openings, such as windows and doors, or through nonpowered ventilatiors or by infiltration.

Negative Pressure
Condition that exists when less air is supplied to a space than is exhausted from the space, so the air pressure within that space is less than that in surrounding areas. Under this condition, if an opening exists, air will flow from surrounding areas into the negatively pressurized space.

Particulate Matter
A state of matter in which solid or liquid substances exist in the form of aggregated molecules or particles. Airborne particulate matter is typically in the size range of 0.01 to 100 micrometers.

Fine liquid or solid particles such as dust, smoke, mist, fumes, and fog found in air and emissions.

An air compartment connected to a duct or ducts.

Preventative Maintenance
Regular and systematic inspection, cleaning, and replacement of worn parts, materials, and systems. Preventive maintenance helps to prevent parts, material, and systems failure by ensuring that parts, materials and systems are in good working order.

A type of thermostat that allows the user to program into the devices’ memory a pre-set schedule of times (when certain temperatures occur) to turn on HVAC equipment.

A refrigerant that is an environmentally sound 50/50 blend of two separate refrigerants, R-32 and R-125. Consumer products featuring Puron refrigerant were first marketed in 1996.

A measure of the capacity of a material to resist heat transfer. The R-Value is the reciprocal of the conductivity of a material (U-Value). The larger the R-Value of a material, the greater its insulating properties.

Radiant Barrier
A thin, reflective foil sheet that exhibits low radiant energy transmission and under certain conditions can block radiant heat transfer; installed in attics to reduce heat flow through a roof assembly into the living space.

Recirculated Air
Air removed from the conditioned space and used for ventilation, heating, cooling, humidification, or dehumidification.

The compound (working fluid) used in air conditioners, heat pumps, and refrigerators to transfer heat into or out of an interior space. This fluid boils at a very low temperature enabling it to evaporate and absorb heat.

The process of the absorption of heat from one location and its transfer to another for rejection or recuperation.

Refrigeration Capacity
A measure of the effective cooling capacity of a refrigerator, expressed in Btu per hour or in tons, where one (1) ton of capacity is equal to the heat required to melt 2,000 pounds of ice in 24 hours or 12,000 Btu per hour.

Return Air
Air that is returned to a heating or cooling appliance from a heated or cooled space.

Return Duct
The central heating or cooling system contains a fan that gets its air supply through these ducts, which ideally should be installed in every room of the house. The air from a room will move towards the lower pressure of the return duct.

Seasonal Energy Efficiency Ratio (SEER)
A measure of seasonal or annual efficiency of a central air conditioner or air conditioning heat pump. It takes into account the variations in temperature that can occur within a season and is the average number of Btu of cooling delivered for every watt-hour of electricity used by the heat pump over a cooling season.

Supply Duct
The duct(s) of a forced air heating/cooling system through which heated or cooled air is supplied to rooms by the action of the fan of the central heating or cooling unit.

Temperature Zones
Individual rooms or zones in a building where temperature is controlled separately from other rooms or zones.

Ton (Air Conditioning)
A unit of air cooling capacity; 12,000 Btu per hour.

A component of a heating or ventilation appliance used to conduct fresh air into, or waste air or combustion gases out of, an appliance or interior space.

Vent Damper
A device mounted in the vent connector that closes the vent when the heating unit is not firing. This traps heat inside the heating system and house rather than letting it draft up and out the vent system.

Caulking, weatherstripping or both to reduce air flow into/out of a home or building.

An area within the interior space of a building, such as an individual room(s), to be cooled, heated, or ventilated. A zone has its own thermostat to control the flow of conditioned air into the space.

The combining of rooms in a structure according to similar heating and cooling patterns. Zoning requires using more than one thermostat to control heating, cooling, and ventilation.

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