Get to Know Your HVAC Words and Terms

HVAC Terms G-Z

Minnesota Carrier

Turn to the experts.

Louvers? You mean lovers right? Nope! When referring to your HVAC unit, we definitely mean louvers. Communicate your home comfort needs with your HVAC technician by using the proper terminology. Stay comfy, Minnesota!


  • A facing across a duct opening, usually rectangular is shape, containing multiple parallel slots through which air may be delivered or withdrawn from a ventilated space.

Heat Load, Heat Loss, or Heat Gain

  • Terms for the amount of heating (heat loss) or cooling (heat gain) needed to maintain desired temperatures and humidities in controlled air. Regardless of how well-insulated and sealed a building is, buildings gain heat from warm air or sunlight or lose heat to cold air and by radiation. Engineers use a heat load calculation to determine the HVAC needs of the space being cooled or heated.


  • Blades, sometimes adjustable, placed in ducts or duct entries to control the volume of air flow. The term may also refer to blades in a rectangular frame placed in doors or walls to permit the movement of air.

Makeup Air Unit (MAU)

  • An air handler that conditions 100% outside air. MAUs are typically used in industrial or commercial settings, or in once- through (blower sections that only blow air one-way into the building), low flow (air handling systems that blow air at a low flow rate), or primary-secondary (air handling systems that have an air handler or rooftop unit connected to an add-on makeup unit or hood) commercial HVAC systems.

Packaged Terminal Air Conditioner (PTAC)

  • An air conditioner and heater combined into a single, electrically-powered unit, typically installed through a wall and often found in hotels.

Roof-Top Unit (RTU)

  • An air-handling unit, defined as either “recirculating” or “once-through” design, made specifically for outdoor installation. They most often include, internally, their own heating and cooling devices. RTUs are very common in some regions, particularly in single-story commercial buildings.

Thermal Zone

  • A single or group of neighboring indoor spaces that the HVAC designer expects will have similar thermal loads. Building codes may require zoning to save energy in commercial buildings. Zones are defined in the building to reduce the number of HVAC subsystems, and thus initial cost. For example, for perimeter offices, rather than one zone for each office, all offices facing west can be combined into one zone. Small residences typically have only one conditioned thermal zone, plus unconditioned spaces such as unconditioned garages, attics, and crawlspaces, and unconditioned basements.

Variable Air Volume (VAV) System

  • An HVAC system that has a stable supply-air temperature, and varies the air flow rate to meet the temperature requirements. Compared to CAV systems, these systems waste less energy through unnecessarily-high fan speeds. Most new commercial buildings have VAV systems.

If you’re interested in learning more about any of these products or technologies, contact your local Minnesota Carrier Factory Authorized Dealer. You can find the one closest to you at

Minnesota furnace repair

For more energy saving and home comfort tips, visit! Stay Comfy, Minnesota is your Minnesota resource for air conditioning repair, furnace repair and HVAC tips and advice.

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