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Plumbing, Heating & Refrigeration Glossary

Learn the Language

Want to understand your contractor better? Or maybe you need a refresher course in a few of the hundreds of acronyms used every day in the heating, plumbing and cooling industry. The terms below are some of the most commonly used - from AFUE to Zoning, you can learn a little more about it here.

List of Terms
Annual Fuel Utilization Efficiency. Measures thermal efficiency for combustion equipment such as furnaces, boilers, and water heaters. Higher numbers denote higher efficiency. AFUE attempts to represent the season-long average efficiency for a piece of equipment. If estimating annual or seasonal energy used by combustion devices, AFUE is the best type of measure to use.
Air Handler- or AHU (air handling unit)
Conditions and circulates air and is part of the HVAC system. The device has a large metal box that contains heating or cooling elements, a blower, sound attenuators, dampers, and filter racks or chambers. AHUs usually connect to ductwork that distributes the air throughout the building.
British Thermal Unit. A unit of energy equal to about 1,055 joules. This amount of energy is the amount needed to heat 1 pound of water from 39 to 40 ° F, or one degree. This unit of measurement is most commonly used in the steam generation, heating, and air conditioning industries. Furnaces and air conditioners usually have BTU ratings: lower ratings mean that the heating or cooling unit has a smaller capacity.
The ability of an HVAC system to heat or cool a certain amount of space. The capacity for heat is measured by BTUs and the capacity to cool is usually measured in tons. The separate units of an HVAC system (blower, ducts, evaporator coil, refrigerant lines) must all have the accurate capacity to preform their roles. A sizing service is sometimes necessary to determine what capacity heating or cooling unit is appropriate for a building.
Certified matched system
A certified matched system is required for the indoor coil unit and outdoor condensing unit of split central air conditioning to work as a team. Each system has a unique Certified Reference Number. A certified matched system can be found in a directory and will generate an AHRI (Air Conditioning, Heating and Refrigeration Institute) Certificate of Product Ratings that ensures the system will perform as promised under certain conditions.
The central functioning unit of an HVAC cooling system. The compressor pumps refrigerant gas up to a high pressure and temperature. The gas then releases its energy outside as hot air.
Condenser Coil
Part of the outdoor portion of an HVAC unit. The condenser coil converts heated gaseous refrigerant back into a liquid. The condenser coil then sends the refrigerant outside.
Valve or plate that regulates the air flow inside a duct or HVAC unit. Dampers may be opened or closed to direct airflow in a building.
Downflow Furnace
Type of furnace that takes in cool air at the top and emits heated air at the bottom. Downflow furnaces are typically installed in the upper levels of a home, or in the attic.
One of the most important units of an HVAC system. Ducts are used for ventilation, heating, and air conditioning. Ducts provide airflow for return air, supplied air, and exhaust air. Ducts are typically made of metal, fiberboard, or some kind of flexible material.
Electronic Air Cleaner
Cleanses the air of small particles and contaminants that have been magnetized, such as infectious bacteria, and draws them into a collector plate.
Evaporator Coil
Part of the HVAC unit that is located inside the air handler. It absorbs the heat from the air in the house.
Heat Exchanger
Device that evaporates heat inside control panels. A heat exchanger enables the inside and outside of the control panel to be isolated, so that mediums are never mixed.
Heat Pump
A device that moves heat from one location (the source) that is at a lower temperature to another location (the sink) that is at a higher temperature. A heat pump can also be used to transfer heat from a storage unit outside to heat a building.
Horizontal Flow
Is a type of furnace that is installed on its ‘side’ and draws air from one side. The air is then heated and is sent out the other side. A horizontal flow system is most commonly used for attics and crawl spaces.
Heating Seasonal Performance Factor is used to measure the efficiency of air source heat pumps. The scale is from low to high, with high being the most efficient.
Device that increases the humidity, or moisture, in a room. Humidifying units can range from small units that heat a single room, to large units that are attached to the HVAC heating unit for the entire house.
Heating, Ventilation, and Air Conditioning. The term can include air conditioners, furnaces, thermostats, filters, and ductwork. The goal of an HVAC unit is to balance indoor comfort with other factors such as installation cost, ease of maintenance, and energy efficiency.
A substance that is used in the heat cycle of an HVAC unit to cool air.The most traditional refrigerants are fluorocarbons and chlorofluorocarbons, but these are being phased out because of their negative environmental effects. Other alternatives for refrigerants include ammonia, sulfur dioxide, and non-halogenated hydrocarbons, such as methane.
Seasonal Energy Efficiency Ratio. Measures an HVAC unit’s cooling efficiency. The scale is measured from low to high, with high being the highest efficiency.
Single Package
An outdoor HVAC unit that contains both the heating and cooling system in a single unit.
Process prior to HVAC installation by which a building is examined to determine optimal capacity HVAC or water treatment unit. Sizing takes into account such things as number of windows and doors, quality of insulation, and gallons of running water.
Split System
An air conditioner or heat pump that is combined with indoor components ranging from an evaporator coils inside the house to a condenser coil outside.
Monitoring device that regulates the temperature inside a building. This device automatically responds to changes in temperature by activating a heating or cooling system to keep the desired temperature range.
Ton (of air conditioning)
Phrase referring to the capacity of a cooling unit. Capacity is measured in relation to the BTUs required to melt one ton of ice in 24 hours (288,000 BTUs). Capacity of air conditioners is measured in BTUs/hr. For example, a 2-ton air conditioner has a nominal capacity of about 24,000 BTUs/hr.
Upflow Furnace
A type of furnace that draws cool air from the bottom and pushes heated air to the top. Upflow furnaces are typically installed in basements.
Mechanism that changes or replaces stale or ‘old’ air with fresh or ‘new’ air.
Method by which energy efficiency in a house may be increased. Zoning enables a user to control heating and cooling delivered to specific areas of a house.
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