At Stelter & Brinck, we design and manufacture custom process air heaters, among other combustion systems. From direct-fired duct, packaged, and gun-style units to indirect-fired recirculating, non-recirculating and straight-through models, our equipment powers critical industrial processes worldwide — drying, curing, heat treating, makeup air, food processing, metals preheating, and more.

Customers often have the same key questions when evaluating process air heaters. Here are the most frequently asked questions (and our straightforward answers) to help you choose the right solution for your application.

1. What is the main difference between direct-fired and indirect-fired process air heaters?

• Direct-fired air heaters mix combustion products directly with the process airstream. This delivers the highest efficiency, lower fuel costs, and compact designs. Stelter & Brinck offers duct-style, packaged, and gun-style direct-fired heaters — ideal for processes where combustion byproducts are acceptable.
• Indirect-fired air heaters use a heat exchanger to separate combustion gases from the process air, delivering contaminant-free heated air. Efficiency is slightly lower, but they excel in food, pharmaceutical, dairy, chemical, or enclosed applications. Our indirect models include recirculating (including USDA-compliant versions), non-recirculating, and straight-through configurations.

Bottom line: Choose direct-fired for maximum efficiency and cost savings when air purity isn’t critical. Choose indirect-fired for clean, sensitive, or regulated processes.

2. When should I choose an indirect-fired air heater over a direct-fired one?

Opt for indirect if your process involves:

• Heat-sensitive or food-grade products (dairy drying, baking, pharmaceuticals, ect.)
• Strict cleanliness or regulatory requirements (USDA, FDA, or low-contaminant specs)
• Enclosed or recirculated systems where combustion byproducts could accumulate

Stelter & Brinck’s indirect-fired heaters are custom-engineered for these demanding applications, with options like USDA-compliant designs for sanitary environments.

3. What airflow rates and temperature rises can your process air heaters handle?

Our heaters are fully custom — we’ve supplied units from a few hundred SCFM up to very large industrial flows, with temperature rises from 50°F to over 2000°F (and higher in specialized designs). Key factors we consider:

• Inlet temperature and desired outlet temperature
• Actual vs. standard CFM (accounting for altitude, pressure, humidity)
• Process mass flow and heat load

We use proven sizing methods and perform in-house test-firing to verify performance before shipment, when possible.

4. How efficient are Stelter & Brinck air heaters, and what fuels do they support?

• Direct-fired: Highest thermal efficiency possible (low excess air, optimized combustion).
• Indirect-fired: 80–85% typical, with high-efficiency heat exchangers and low-emission burners.

We support natural gas, propane, #2 fuel oil, dual-fuel, and other gaseous/liquid fuels — with low-NOx burners available for emissions compliance.

5. What about maintenance, safety, and service life?

Our heaters are built for rugged industrial duty with heavy-gauge construction and proven components. We offer:

• NFPA-compliant designs
• Scheduled burner maintenance programs (tuning, leak tests, inspections)
• Field rebuilds, upgrades, retrofits, and parts
• In-house combustion test-firing before shipment for reliability

Many of our systems have operated reliably for decades with proper service.

6. Do you provide USDA-compliant or sanitary air heaters?

Yes — our recirculating indirect-fired air heaters can be built to USDA standards for dairy, food, and sanitary processes. These feature smooth surfaces, accessible cleanouts, and materials suited for washdown environments.

7. How do I get started with sizing or quoting a Stelter & Brinck process air heater?

Contact our team with basic info:

• Process airflow
• Inlet and desired outlet temperatures
• Application details (product sensitivity, location, fuel type, emissions needs)
• Any special requirements (recirculation, pressure, altitude)

We’ll provide a tailored recommendation and quote — backed by our engineering expertise.

Need expert guidance on your next process heating project?

Stelter & Brinck has powered industry with clean, efficient heat since 1921. From custom indirect and direct-fired process air heaters to combustion services and environmental systems — we’re your partner for performance and reliability. Whether you’re upgrading an existing system or designing a new one, reach out today:

📞 513-367-9300 🌐 stelterbrinck.com 📧 Contact form on our site