HVAC Terminology Guide

Key Term Categories

General


AIR BALANCING	Adjusting the air distribution system so that the right amount of air is delivered to the right places in your home to achieve the right heating or cooling effect.
AIR HANDLING UNIT	Equipment with a heating element and/or cooling coil and other components in a cabinet or casing.
AHRI	Air-Conditioning, Heating and Refrigeration Institute, a non-profit, voluntary organization composed of heating, air conditioning and refrigeration manufacturers. AHRI publishes standards for testing and rating heat pumps and air conditioners.
BUILDING ENVELOPE	Elements of the building, including all external building materials, windows, and walls, that enclose the internal space.
CONDITIONED AIR	Air that has been heated, cooled, humidified, or dehumidified to maintain an interior space within the comfort zone.
COMMISSIONING	The final step in installing a heating or air conditioning system. Every component is checked and tested for compliance with codes, manufacturer requirements, and occupant needs. After commissioning, the technician will: provide documentation of testing, provide all equipment manuals, and show the homeowner how to operate the system.
DEHUMIDIFIER	A device that removes excess moisture from the air.
DUCTWORK	Conduits used to carry air. They can be round or rectangular, sheet metal or fiberglass. In air conditioning systems they carry air from the home to the air conditioning system or furnace and back to the home.
ERV	Energy Recovery Ventilator, a machine that draws fresh air into the home and exhausts stale air from the home. It uses a process to preheat or pre-cool (depending on the season) to reduce energy costs associated with conditioning the air.
HVAC	Heating, ventilating, and air conditioning
HRAI	Founded in 1968, the Heating, Refrigeration and Air Conditioning Institute of Canada, a non-profit, voluntary organization composed of heating, air conditioning and refrigeration manufacturers.
HYDRONIC HEAT	Heat transferred from a boiler, to conditioned water, to a radiator in the living space.
INFILTRATION	Air that enters your home through holes, gaps, and cracks, (e.g., plumbing, or electrical holes, the heating and air conditioning system, doors, and windows).
LOAD CALCULATION	A mathematical determination of how much cooling and heating (BTUs) an HVAC system must deliver for occupant safety and comfort. It is based on a variety of factors: square footage, building orientation, number of occupants, size and placement of rooms, number and size of windows and doors, amount of insulation, number of floors, and climate.
MANUAL J®	An ACCA procedure covering the method for calculating heating and cooling requirements (load calculation) for single-family detached homes and mobile homes.
MATCHED SYSTEM	An air conditioner or heat pump system composed of equipment that has been certified by ARI to work together to deliver the specified heating and cooling capacity at the stated efficiency rating.
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.
RETURN AIR	The path the air takes to get to an air-handling unit or furnace so it can be cooled or heated. It is the “return” path. The return side should be “balanced” with the supply side to ensure proper air flow and comfort.
STATIC PRESSURE	In flowing air, the total pressure minus velocity pressure. The portion of the pressure that pushes equally in all directions.
SUPPLY AIR	The part of an HVAC system that takes (supplies) the conditioned air from the air- handling unit or furnace to your home. The supply side should be “balanced” with the return side to ensure proper air flow and comfort.
ZONING	A single HVAC system that can meet different heating and cooling needs in different areas (zones). Each zone of a home has its own thermostat with which it can regulate the temperature and humidity in its area. One “zoned air conditioner” could be set for a high temperature in one zone and for a lower temperature in the other zone. Zone systems have two or more zones.

Cooling


BTU	British Thermal Unit, the measurement of air conditioning capacity. One BTU is the amount of heat that must be added to one pound of water to raise its temperature one degree Fahrenheit.
CFC	Chlorofluorocarbons, used as a refrigerant in air conditioners and heat pumps, linked to the depletion of the ozone layer.
CFM	Cubic feet per minute.
CONDENSER	The outside unit of a heating or air conditioning system. Here the refrigerant condenses from a gas to a liquid and hot or cold air from the building is released to the outside.
COP (Co-efficient of Performance)	A heat pump performance indicator. An efficiency ratio that compares the amount of heat delivered to the amount of energy used.
COOLING COIL	Component of HVAC system that acts as a heat exchanger, either adding heat or taking heat away from the air stream.
ENERGY STAR®	A government supported branding used to identify energy efficient products. The branding was developed by the US Department of Energy and the US Environmental Protection Agency.
HEAT PUMP	A single refrigeration system designed to provide both heating and cooling
HFC	Hydrofluorocarbon, used as a refrigerant in air conditioners and heat pumps. It has little or no effect on the ozone layer.
HCFC	Hydrochlorofluorocarbons, used as a refrigerant in air conditioners and heat pumps. HCFCs were thought to contribute to the depletion of the earth’s ozone layer.
HSPF	Heating Seasonal Performance Factor, an equipment efficiency rating generally used for heat pumps.
LATENT HEAT	The energy that suspends moisture vapor in the air.
R-22	A refrigerant containing chlorine used in air conditioning systems. The EPA has mandated that R-22 cannot be manufactured after 2010 because it has been linked to the depletion of the ozone layer and global warming
R-410A	The refrigerant that replaces R-22. It does not contain chlorine and is not hazardous to the environment.
REFRIGERANT	A fluid that absorbs heat at low temperatures and rejects heat at higher temperatures.
REFRIGERANT CHARGE	The procedure an HVACR technician performs to ensure that the system has enough of the right kind refrigerant for peak operating performance.
SEER	Seasonal Energy Efficiency Ratio, an equipment efficiency rating that measures how much energy it takes to cool the air. The higher the number the more efficient the unit.
SENSIBLE HEAT	The temperature of the air. This type of heat is measured with a thermometer.
SPLIT SYSTEM	A two-component heating and cooling (heat pump) or cooling only (air conditioner) system. The condensing unit is installed outside, the air handling unit is installed inside(preferably in conditioned space). Refrigerant lines and wiring connect them together

Heating


BTU	British Thermal Unit, the measurement of heating capacity. One BTU is the amount of heat that must be added to one pound of water to raise its temperature one degree Fahrenheit.
CO	Carbon monoxide.
COMBUSTION AIR	Additional air brought into the house to allow furnaces, boilers, clothes dryers, ranges, and domestic hot water heaters to burn. If the appliance has “sealed” combustion this air will not affect the air within the house.
ENERGY STAR®	A government supported branding used to identify energy efficient products. The branding was developed by the US Department of Energy and the US Environmental Protection Agency.
FPM	Feet Per Minute describes velocity of air. FPM is always positive and measured in one direction
FURNACE	A self-contained heating unit that is designed to deliver heated air to the home.
GAMA	Gas Appliance Manufacturing Association is a national trade association serving the interests of manufacturers of gas, oil, and electric appliances and equipment,
HEATING COIL	A heating element made of pipe or tubing, usually with plates or fins. A device intended to allow the contents of the coil (generally refrigerant or hot water) to heat the air as it passes through it.
HEAT EXCHANGER	The part of a furnace that transfers heat from burning fuel to the air used to heat your home. Also, from a boiler to water for hydronic heating. A device, such as a condenser or evaporator, in which heat is added or removed to heat or cool your home.
SUPPLY PLENUM	The main air compartment connected to a duct or ducts above the furnace.

Air Purification


ACH (Air Exchanges per Hour)	Computed by taking the cubic area of a space and dividing it by the volume of air per hour supplied to it.
ELECTRONIC AIR CLEANER	Use electrically charged filters to reduce the number of airborne contaminants in your home. As air passes through your heating and cooling system, the electronic air cleaner traps large particles (such as dust and dander) in a prefilter.
HEPA AIR CLEANER	High Efficiency Particulate Air Filter. 99.97% efficiency capturing particulate down to 0.3 micrometer particles.
IAQ	Indoor air quality describes the quality of the air to an interior space. The goal if IAQ is to provide air that is clean and healthy to building occupants
MEDIA AIR CLEANER	The main difference between a media air cleaner and a standard air filter is size. Conventional air filters are an inch thick while media cleaners are 4 to 5 inches thick. This allows for more and better air filtration.
MERV	Minimum efficiency reporting value refers to the lowest efficiency of a filter when tested in accordance with ANSI/ASHRAE standard 52.2 2017.
PRESSURE DROP	The resistance of a device to the flow of fluid through it. A pressure drop of a filter is a measure of its resistance to airflow through it. Resistance is measured in inches of water gauge.
UV DISINFECTION	Ultraviolet (UV) germicidal light, produced by special lamps, is sometimes used to inactivate the bacteria and viruses present in airborne particles, making the bacteria and viruses unable to cause infectious disease in people.
VOLATILE ORGANIC COMPOUNDS	Compounds that evaporate from housekeeping, maintenance, and building products made with organic chemicals. These compounds are released from product that are being used and are in storage. In sufficient quantities, VOCs can cause eye, nose, and throat irritations, headaches, dizziness, visual disorders, memory impairment; some are suspected of causing, or are known to cause, cancer in humans.

Humidification


BYPASS HUMIDIFIER	A whole house type where warm arm air that comes through the furnace and pass it through an evaporator pad to moisten it. This humid, warm air is then released into your house through the ducts.
HUMIDIFIER	A device that adds moisture to warm air for your home.
FAN POWERED HUMIDIFIER	Whole house type with an internal fan that pushes the air from the duct to the humidifier for moisturizing, then back into the same duct.
RELATIVE HUMIDITY (RH)	The percent of moisture in the air compared to the maximum amount of moisture the air can hold at that temperature.
STEAM HUMIDIFIER	These humidifiers work by sensing the current humidity level at our home using the inbuilt humidistat. Upon sensing a need, they electrically boil water to produce steam, which then travels through the HVAC system of your house to induce humidity.