Bottom Line Up Front
The Reznor UDXC is the separated combustion unit heater that dominates North American warehouse, garage, and industrial facility heating. Separated combustion draws combustion air from outside and exhausts directly to the exterior — eliminating the indoor air quality concerns of conventional unit heaters and enabling installation in spaces with contaminated atmospheres. The 20-year heat exchanger warranty is the longest in commercial unit heaters. Reznor's service network and parts availability are the standard by which competitors are measured.
Spec Sheet
| Model | UDXC-30 |
| BTU Input | 30,000 BTU/hr |
| Efficiency | 80% AFUE |
| Fuel | Natural gas (LP convertible) |
| Type | Separated combustion |
| Air Volume | 480 CFM |
| Voltage | 120V / 60Hz |
| Clearances | 18" sides, 48" below |
| Warranty | 20-year heat exchanger, 5-year parts |
| Price | $800–$1,500 installed |
Extended Analysis
Separated combustion (also called direct combustion or sealed combustion) is the specification requirement in any commercial or industrial space where combustion air quality cannot be guaranteed. Paint booths, chemical storage areas, tire shops, and any space with flammable vapors require separated combustion to prevent contamination of the combustion air and eliminate ignition risks.
Even in spaces without flammable concerns, separated combustion provides air quality and draft advantages. Conventional unit heaters draw combustion air from the heated space, creating a slight negative pressure that can cause back-drafting from other combustion appliances or allow exterior cold air infiltration through building penetrations. Separated combustion eliminates these interactions.
The UDXC's 80% AFUE (Annual Fuel Utilization Efficiency) places it in the standard efficiency tier for commercial unit heaters. High-efficiency condensing unit heaters (90-95% AFUE) are available but add significant cost and require condensate drainage. For spot heating applications with moderate runtime hours, 80% AFUE is typically the cost-optimal choice. For continuous industrial heating with 4,000+ annual operating hours, condensing units' efficiency premium can justify the premium.
How It Compares
| Model | Efficiency | Price | Key Spec | Score | Type |
|---|---|---|---|---|---|
| Reznor UDXC-30 | 80% AFUE | $800–$1,500 | 20-yr HX warranty | ★★★★★ 4.7 | Separated combust. |
| Sterling GG Series 30K | 80% AFUE | $750–$1,400 | 10-yr HX warranty | ★★★★☆ 4.3 | Separated combust. |
| Modine PTP-30 | 82% AFUE | $850–$1,600 | 10-yr HX warranty | ★★★★☆ 4.4 | Separated combust. |
Customer Reviews
We have 24 Reznor UDXC units across our manufacturing facility. The oldest units are 18 years old and still running. The separated combustion was required by our insurance carrier given the painting operations in the facility. In 18 years, we have had one heat exchanger failure (covered by warranty) and three igniter replacements. This is the most reliable product in our mechanical portfolio.
Replaced 12 conventional unit heaters with UDXC separated combustion units after OSHA flagged our old setup in a facility with chemical storage. The installation was straightforward with the exterior combustion air and exhaust connections. The heaters have performed reliably through three Chicago winters. The 20-year heat exchanger warranty gives us a long planning horizon for our maintenance budget.
Reznor is the standard specification for Minnesota commercial applications requiring separated combustion. The units are reliable, parts are universally available, and inspectors know the product. My only note is that the 80% efficiency leaves money on the table for high-usage applications — for a warehouse running heating 8 months per year, a condensing unit pays back quickly. But for most applications, the UDXC is the right choice.
Frequently Asked Questions
What is separated combustion and why does it matter?
Separated combustion units have two dedicated pipes: one drawing combustion air from outside the building and one exhausting combustion products to the exterior. This is in contrast to conventional unit heaters that draw combustion air from the heated space. Separated combustion eliminates indoor air quality impacts from combustion, prevents back-drafting, and is required in spaces with contaminated atmospheres (flammable vapors, paint, chemicals).
What is the clearance requirement for the Reznor UDXC?
18 inches on sides and 48 inches below the unit to combustible materials. The unit requires unobstructed airflow for the propeller fan. Combustion air intake and exhaust connections penetrate the exterior wall with provided fittings. Minimum 1-foot clearance from corners is recommended for adequate combustion air distribution.
Can the Reznor UDXC run on propane?
Yes. The UDXC ships configured for natural gas and includes a conversion kit for LP (propane) operation. LP conversion requires a certified technician to replace the orifices and adjust the regulator. LP versions deliver the same BTU output but at higher gas pressure settings.
What controls are available for the Reznor UDXC?
Standard 24V thermostat control. The UDXC is compatible with standard commercial thermostats and building automation systems. Modulating gas valve options are available for some sizes to improve efficiency at partial load. Remote setback capability is standard through any compatible 2-stage thermostat.
What is the warranty on the Reznor UDXC?
20-year limited warranty on the heat exchanger and 5 years on all other parts with registration. The 20-year heat exchanger warranty is the longest in the commercial unit heater category. Reznor's warranty service is handled through their authorized contractor network with parts available next-day from Reznor distributors nationally.