A Glossary Of HVAC Technical Definitions

AFUE - The ratio of annual output energy compared to annual input energy. The higher the AFUE percentage is, the more efficient the furnace. Annualized Fuel Utilization Efficiency (AFUE) is a measure of your furnace’s heating efficiency.

Airflow - The distribution or movement of air Air Handler/Coil Blower. Air flow volume is measured in CFM (cubic foot per minute)

AHRI Reference Number - This is a unique numerical representation for a condenser and evaporator combination that has been certified and identified by Air-Conditioning, Heating, and Refrigeration Institute. Many efficiency program administrators will require this number to be submitted with incentive applications.

Btu - Btu stands for British thermal unit, which is a unit of heat energy. One Btu is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

Btu/h - British thermal units per hour. A unit of the rate of energy consumption or delivery.

Carbon Monoxide (CO) - Often called the silent killer, CO is an invisible, odorless, colorless gas created when fuels (such as gasoline, wood, coal, natural gas, propane and oil) burn with inadequate amounts of oxygen, creating a condition known as incomplete combustion. In the case of home gas appliances, this can be caused by improper installation, poor maintenance, or other appliance misuse or failure. When incomplete combustion occurs in a home’s gas appliances, CO is produced, and this can lead to CO poisoning.

Capacity - The ability of a heating or cooling system to heat or cool a given amount of space. For heating, this is usually expressed in BTU/h. For cooling, it is usually given in tons.

Central Air Conditioning System - System in which air is cooled at a central location and distributed to and from rooms by one or more fans and a series of ducts.

Certified Matched System - A heating and cooling system comprised of equipment that has been certified to perform at certified efficiency levels when used together, and used according to design and engineering specifications. The Air-Conditioning, Heating, and Refrigeration Institute (AHRI) puts heating and cooling equipment through rigorous certification processes to ensure systems deliver the efficiency performance at certain test conditions.

CFM - Cubic Feet per Minute. This measurement indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being moved through the ductwork by the system.

Compressor - The outdoor portion of an air conditioner or heat pump that compresses and pumps refrigerant to meet household cooling requirements.

Condenser Coil - The outdoor portion of an air conditioner or heat pump that either releases or collects heat, depending on the time of the year.

Combustion - Combustion takes place when gaseous, liquid or solid fuels react at an elevated temperature with oxygen by burning, thus releasing heat. For good combustion, an adequate supply of oxygen must be available, and all the carbon in the fuel will be converted to carbon dioxide and all the hydrogen to water vapor.

Condensate (Condensation) - The liquid that separates from a gas due to a reduction in temperature or an increase in pressure.

Damper - When used in ductwork, the damper is a movable plate that regulates airflow. Dampers are used to direct air to the areas that need it most. Typically used in zoning applications. dB A decibel is a unit used to measure the relative intensity of sound.

DOE - Abbreviation for the U.S. Department of Energy, the federal agency responsible for setting national appliance efficiency standards and monitoring the consumption of energy sources.

Ductwork - The system by which air is channeled from the furnace or the blower coil throughout your home.

Electronic Air Cleaner - An electronic device that filters out large particles and bio-aerosols in indoor air.

EF - Energy Factor The amount of energy delivered as heated water in a day divided by the total daily energy consumption of a residential water heater. The EF is used to compare the energy efficiency of models. Water heaters with higher EFs will have lower annual operating costs than comparable models with lower EFs.

Energy Guide Label - A large yellow tag affixed to major appliances and HVAC equipment such as central air conditioners, heat pumps, furnaces, water heaters and boilers that provides energy efficiency and operating cost information. The label is designed to help consumers compare the operating cost of similar models.

Energy Input Rating - The amount of input energy delivered at the burner of furnaces, water heaters and boilers, measured in British thermal units (Btus) per hour.

ENERGY STAR® - An EPA designation attached to HVAC equipment to identify models that meet EPA guidelines for high-efficiency performance that exceed standard government minimums. Manufacturers and retailers place the ENERGY STAR® label on those models that meet the labeling criteria. The label helps consumers identify those products that will save money and energy.

EPA - An abbreviation for the U.S. Environmental Protection Agency, the federal agency that develops and enforces federal environmental regulations. The EPA oversees the nationwide ENERGY STAR® program.

Evaporator Coil - The part of the air conditioner or heat pump that is located inside the air handler or attached to the furnace. Its primary function is to absorb the heat from the air in your house.

Flow Rate - The amount of water in gallons flowing past a fixed point over a period of time, typically expressed in gallons per minute.

FLUE - The passageways in heating equipment and vents through which combustion products pass to the outside atmosphere.

FLUE Collar - The portion of a gas appliance designed for the attachment of a venting system.

GAMA - The GAMA Efficiency Rating Certified logo appears on space and water heating equipment that has been certified by the Air-Conditioning, Heating and Refrigeration Institute. It is your guarantee that the equipment’s energy-efficiency ratings have been independently verified by a third party. Space and water heating equipment displaying the GAMA emblem includes furnaces, water heaters, boilers and direct heating equipment.

GPH (Gallons Per Hour) - A measure of water use for water heaters.

GPM (Gallons Per Minute) - The amount of water flowing through a plumbing fixture or pipe to your water heater. Heat Exchanger A component of furnaces, the heat exchanger transfers heat to the surrounding air, which is then distributed throughout the home.

Horizontal Flow - When an air handler or furnace is positioned on its side and circulates air in one end and out the other. Ideal for attic or crawl space installations.

HSPF - The Heating Seasonal Performance Factor is the heating efficiency rating for heat pumps. The higher the rating, the more efficient the heat pump. Humidistat An automatic device used to maintain humidity at a fixed or adjustable set point.

HVAC - Heating, Ventilation, and Air Conditioning

HVACR - Heating, Ventilation, Air Conditioning, and Refrigeration

Load Calculation - Load calculations consider a variety of factors: location (Boston’s weather is different than that of Los Angeles), orientation (southwest glass gets much more sun than north glass), construction materials (insulation, brick or siding, etc.), building size, etc. Heating and cooling needs are expressed in BTUs per hour or Btu/h. A “block load” looks at the whole building’s requirements as one large room. A “room-by-room” load calculation refines the calculation to determine a room or zone’s requirements.

Manual J Calculation - A residential load calculation procedure, based on an accepted industry standard (approved by the American National Standards Institute) used for the proper sizing and selection of HVAC equipment in residential homes.

MERV Rating - The MERV (Minimum Efficiency Reporting Value) rating of a filter describes the size of the holes in the filter that allow air to pass through. The higher the MERV rating, the smaller the holes in the filter, the higher the efficiency.

Micron - A unit of length equal to one millionth of a meter, or one thousandth of a millimeter. Odors/Chemicals Air contaminants in the form of gases. Particles Any substances measuring less than 100 microns in diameter. The EPA has found that small particles (less than 2.5 microns) are responsible for the health effects of greatest concern.

Pilot - A small gas flame utilized to ignite gas at a main burner of heating equipment.

Programmable Thermostat - A thermostat with the ability to preset different temperature/time settings for your heating and cooling equipment.

Recovery Efficiency - The ratio of energy delivered to heat cold water compared to the energy consumed by the water heater.

Reclaiming - Returning used refrigerant to the manufacturer for disposal or reuse.

Recycling - Removing, cleaning and reusing refrigerant. Refrigerant A chemical that produces a cooling effect while expanding or vaporizing.

R410A Refrigerant - A chlorine-free refrigerant that meets the EPA’s newest, most stringent environmental guidelines.

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

Scroll Compressor - A compressor that works in a circular motion, as opposed to up-and-down piston action.

SEER - The Seasonal Energy Efficiency Ratio is an energy efficiency rating for air conditioners. The higher the SEER, the better the energy performance, the more you save. The DOE’s established minimum SEER rating for cooling is 13.00. Single Package A heating and cooling system contained in one outdoor unit.

Standby Loss Heat - Energy that escapes stored water in a tank-type water heater, requiring that water to be heated even when there is no demand. Manufacturers reduce standby loss in tank water heaters by insulating the tank.

Split System - The ratio of annual output energy compared to annual input energy. The higher the AFUE percentage is, the more efficient the furnace. Annualized Fuel Utilization Efficiency (AFUE) is a measure of your furnace’s heating efficiency.

Temperature Rise - The difference between the inlet cold water temperature and the heated water temperature that your water heater delivers.

Thermal Efficiency - The ratio of energy delivered as heated water compared to the energy consumed by your water heater.

Thermal Expansion Valve - The metering device or flow control that regulates the amount of liquid refrigerant allowed to enter the evaporator.

Thermidistat - A device that monitors temperature and humidity and adjusts your heating or cooling system to maintain desired levels.

Thermostat - Usually found on an inside wall, this device operates as a control to regulate your heating and cooling equipment, allowing you to adjust your home comfort at the touch of a switch.

Ton - Unit of cooling capacity. A “ton” of air conditioning refers to capacity in relation to melting one ton of ice in 24 hours. 288,000 Btu are required to melt one ton of ice in 24 hours (or 12,000 Btu/hr). A 2-ton air conditioner has a nominal capacity of about 24,000 Btu/h.

Two-Stage Operation - Provides two levels of heating or cooling output for greater temperature control, energy efficiency and improved indoor air quality. Upflow When an air handler or furnace is installed in an upright position and circulates air through the side or bottom and out through the top. Typically used in basement, closet and attic installations.

Variable Speed Motor - A motor that automatically adjusts the flow of warm or cool air for ultimate comfort.

Ventilator - A system that exchanges stale, re-circulated indoor air with fresh, filtered outside air.

Venting - Removal of combustion products and process fumes to the outer air.

Venting System - A continuous open passageway from the flue collar or draft hood of a gas-burning appliance to the outside atmosphere for the purpose of removing products of combustion.

Zoning - A method of partitioning a home into independently controlled comfort zones for enhanced comfort and efficiency.