Recirculating Heated Make-up Air Unit
Tempering a full stream of outside air carries a heavy heating load, and in a cold climate that load drives your fuel use straight up.
A recirculating heated make-up air unit, or RMUA, answers that by blending return air with outside air before it heats anything. The mixed air enters warmer than raw outside air, so the burner or coil does far less work to reach discharge temperature.
The blend happens in a mixing box. Modulating outside-air, return-air, and relief dampers set the ratio, hold your discharge temperature, and keep building pressure where you want it. Recirculated air heating fits high-bay shops, warehouses, and large commercial spaces where the return air stays clean and code permits it.
Below you get the configurations, the ratios and CFM ranges, the load math, and what an engineer needs to spec one.
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We are the authorized distributors for the leading American manufacturers of indirect gas-fired make-up air units. We’ll be pleased to provide the ideal make up air unit for your application as authorized representatives.
For a fast quote or if you have inquiries about commercial or industrial MUA, get in touch with us.
Recirculation ratios and CFM
Recirculation is adjustable across the range, modulating down to full outside air whenever the space needs it.
| Parameter | Typical Range or Value |
|---|---|
| Recirculation ratio (RA/OA) | 0 to 80% return air, 80/20 base, modulates to 100% OA |
| CFM capacity | 1,000 to 50,000+ CFM |
| Mixed-air control | Modulating OA, RA, and relief dampers; discharge thermostat ±1°F |
| Discharge setpoint | 55 to 65°F typical |
| Heat source options | Gas, electric, steam, hot water |
| Return-air filtration | MERV 8 to 11 typical industrial |
Heating load and savings
Heating capacity follows a simple formula, and recirculation cuts the temperature rise the heat source has to deliver.
| Scenario | Heating Load |
|---|---|
| Heating capacity formula | BTU/hr = 1.08 × CFM × ΔT |
| 30,000 CFM, 0°F OA, 60°F discharge, once-through | 1,944,000 BTU/hr |
| Same unit, 80% recirculation, 70°F room air (mixed air 56°F, ΔT 4°F) | 129,600 BTU/hr |
| Field savings range, clean recirculated air, cold climate | 50 to 90% |
The 30,000 CFM line is one illustrative case. Real savings depend on your design outside-air temperature, room temperature, and how far the unit modulates, so size to your conditions with the make-up air sizing calculator.
Where recirculation fits
Recirculated air heating works where the return air stays clean and code allows the blend.
| Fits | Does not fit |
|---|---|
| High-bay shops, warehouses, distribution centers | Spaces with grease-laden or contaminated exhaust |
| Non-hazardous manufacturing bays | Flammable vapors, dust, noxious gases |
| Gymnasiums, arenas, large commercial spaces | Hazardous-materials or heavy-process areas |
| Spaces with general-ventilation exhaust and filtration | Restrooms, labs with fume hoods, isolation rooms |
Why Buyers Spec Through Us
Our sales engineers size recirculating heated make-up air units to your building, not to a catalog page. We match the blend range, heat source, and controls to your exhaust load and the air quality in the space.
You get the airflow math, the damper and filtration callouts, and the safety interlocks worked out before the unit ships, so commissioning goes fast. We represent the leading American make-up air manufacturers and pull the right configuration for your application.
Tell us your CFM, design outside-air temperature, and discharge target, and we size it with you. Call 847-262-3457 ext. 23 to start.
Have questions? Need a quote?