Make-Up Air Units (MUAs)

As a part of a heating, ventilating, and air-conditioning (HVAC) system, a rooftop condensing make-up air unit (MUA) is a larger air handler that circulates and conditions 100 percent outside air.

Make-Up Air Units (MUAs)


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How It Works

MUA units are a common form of ventilation. They introduce fresh air into a building and exhaust building air through multiple exhaust fans located all around the building.

MUA units are located on the rooftop of a building and supply 100 percent outdoor air. As shown in the diagram, the MUA takes in fresh outdoor air and passes it through a bank of filters and dampers to remove contaminants and regulate the amount of air brought in.

The incoming air can then be efficiently heated by an indirect gas-fired heat exchanger. The heated air is then either blown directly into a building space or it can be ducted to target locations. Where condensing MUAs really achieve higher efficiencies is during the heating season. The heat exiting the building is extracted and during this process latent heat is released and captured. The latent heat is used to preheat the incoming air from outside, saving energy and improving efficiency.


MUAs require routine maintenance and inspections. Managers should schedule inspections and maintenance on a semiannual basis with a technician from the manufacturer or service provider.


  • Condensing technology offers efficiencies of over 90 percent as compared to the 78 - 82 percent efficiencies of non-condensing MUAs
  • High turn around feature results in better control and comfort
  • Energy efficiency lowers operating costs
  • Improved air quality creates a more comfortable work environment for employees and customers

Building Applications

Most commercial and industrial buildings can benefit from installing a high efficiency condensing MUA unit including, restaurants and commercial kitchens, gymnasiums, auto repair shops, wastewater and sewage treatment facilities, and manufacturing and assembly plants.

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