Direct vs. Indirect Fired Heater Rental

Fired heaters are a cost-efficient way to heat commercial or industrial spaces. They use fuel combustion inside an insulated unit to produce heat, but not all fired heaters work the same. The two main types, direct and indirect, have different strengths, safety levels, and ideal uses. Here’s how they compare so you can choose the right heater for your needs and budget.

When to Use a Direct Fired Heater

Direct fired heaters are the most efficient and affordable type. They burn natural gas or propane with an open flame, sending heated air directly into the space. This design makes them powerful but requires proper ventilation and safety precautions.

Advantages of direct fired heaters include:

• Simple design: No heat exchanger or flue, making installation easier 
• Compact size: Produces more heat in less space 
• High efficiency: Fuel converts into usable heat, with thermal efficiency around 92% 
• Flexible sizing: Available in many BTU ratings to fit different spaces 
• Durability: Built to last with fewer parts than indirect models

When to Use an Indirect Fired Heater

Indirect fired heaters send combustion into a heat exchanger. Exhaust gases are vented outside through a flue so no byproducts enter the indoor air. Some models also include energy recovery or cooling features. This makes them safer and better suited for enclosed or sensitive environments.

Advantages of indirect fired heaters include:

• Safer operation: No combustion gases released indoors 
• Better air quality: Air passes downstream of cooling coils, reducing toxic gas risks .
• Recirculation: Can reheat 100% of indoor air without introducing fumes 
• Ideal for enclosed spaces: Commonly used in offices, schools, arenas, and medical facilities.

Rent Fired Heaters From The Cat^® Rental Store

Both direct and indirect fired heaters can improve productivity and comfort on your site. The Cat^® Rental Store carries heaters from trusted brands, available with flexible rental terms. Browse our full product selection, request a quick quote or find your nearest Cat dealer today.

FAQs About Fired Heaters

What’s the main difference between direct and indirect fired heaters?

Direct heaters release heat straight into the air, while indirect heaters use a heat exchanger to keep combustion byproducts out of the space.

Which type is safer?

Indirect fired heaters are safer since no combustion gases enter the air, making them better for enclosed spaces.

Which is more efficient?

Direct fired heaters are more efficient, converting nearly all their fuel into heat.