Achieve Energy Efficiency With 80/20 Direct Fired Make-Up Air Units

November 8, 2023

Heating a commercial or industrial space can be costly, so as the seasons change owners and facility managers naturally consider ways to minimize this cost. Investing in an 80/20 direct fired make-up air heater should be high on their list.

KEES Model DFG units with the 80/20 option are extremely efficient. The direct-fired heater in each of these units provides 100% combustion efficiency. The 80/20 option allows the unit to recirculate up to 80% of the air volume from the indoor space. Warming this air to the desired temperature requires much less energy than bringing 100% cold outside air up to temperature.

KEES Unit Tames a Tornado

One recent project, the Howlin’ Tornado Water Slide at Great Wolf Lodge, features a KEES make-up air unit that works behind the scenes to keep the air fresh, safe and comfortable for the occupants of the indoor waterpark. For the water park project, the lodge needed a reliable, energy-efficient make-up air unit that came with an independent certification and with on-site training. The result? KEES provided this iconic Wisconsin Dells resort with a unit that moves 17,000 CFM of clean, filtered air.

Wisconsin Dells resort with a unit that moves 17,000 CFM of clean, filtered air.

Precise Controls Ensure Clean Combustion

Recirculating air sounds like a simple concept, but when combined with a direct fired burner, recirculation requires specialized controls. Because the combustion occurs directly in the airstream, ensuring clean combustion is very important. KEES Model DFG make-up air units have clean combustion thanks to a precise control system. ETL has independently tested our units and verified they meet the stringent requirements of ANSI standard Z83.18 for recirculating direct gas-fired heating applications.

Achieving Optimal Efficiency In Large Spaces

Ideal applications for 80/20 DFG make-up air units include industrial and production buildings, warehouses and maintenance facilities for vehicles, trains and aircraft. The 80/20 units can also help control building air pressure. Additionally, they can be used for a wide range of make-up air and/or space-heating applications.

KEES 80/20 DFG Make-Up Air Unit Features

  • ETL listed in accordance with the stringent requirements of ANSI standard Z83.18
  • FM and IRI compliant
  • Airflow capacity up to 30,000 CFM
  • 90-degree maximum temperature rise
  • Switch to 100 percent outside air when maximum ventilation is required
  • Outdoor or indoor installation
  • Vertical or horizontal mounting
  • Optional stainless steel construction or Heresite coating for harsh operating environments

View and download the submittal

KEES 80/20 make-up air units
KEES 80/20 make-up air units can be mounted vertically or horizontally (as shown above), and have many other options and accessories.


In addition to 80/20 DFG units, KEES manufactures numerous air-handling units to offer comprehensive solutions for all your air distribution needs with these advantages:

  • Durable, high-performance motors, fans, dampers and electronic controls
  • 100 percent thermally efficient heaters for maximum energy conservation
  • Customized electronic controls including interfaces for building management systems
  • Easy servicing with removable panels on both sides on every section, generous spacing between components, numbered terminal strips and wiring raceways.
  • Optional stainless steel construction for harsh operating environments
  • Full line of accessories enables customized solutions

Learn more about KEES make-up air units