Direct Fired Heater
A direct fired heater burns fuel — typically propane or natural gas — directly in the airstream it delivers, putting nearly all the fuel's energy into the space as heat. The tradeoff is that combustion products enter the heated air, so these heaters belong in open, well-ventilated spaces. The catalog lists 142 models from brands including Modine, Master, Remington, Trane, Qmark and Lennox.
How it works
A burner fires into the airflow from an integral fan; air passes through the flame zone and carries the heat — and the combustion byproducts — into the space. With no heat exchanger, efficiency approaches the fuel's full value and the equipment stays simple, light and inexpensive per BTU. Because carbon monoxide, carbon dioxide and water vapor discharge with the heated air, ventilation requirements are absolute: fixed fresh-air openings or mechanical ventilation sized per the manufacturer and applicable code.
Types & variants
- Portable forced-air heaters
- Compact propane and gas units for spot and small-area heat.
- High-output construction heaters
- Large box and salamander formats for open structures and enclosures.
- Suspended unit heaters
- Fixed gas-fired heaters for garages and industrial bays.
- Tent and ground-thaw configurations
- Ducted direct-fired setups for temporary structures and frozen ground.
Key specifications
| Specification | Typical range | What it means |
|---|---|---|
| Heat output | Up to 50,000 through 400,000 BTU + across the catalog size classes | BTU per hour — the sizing figure against space volume and temperature rise. |
| Airflow | 150 to 2,182.5 cfm documented across listed models | Delivered air volume spreads the heat through the space. |
| Fuel type | Documented per model listing | Propane, natural gas or dual-fuel decides supply logistics. |
| Fuel capacity | 7 to 20 gal documented on tank-equipped models | Onboard fuel sets run time between refills where cylinders are not used. |
How the industry sizes it
Direct fired heaters are sized in BTU per hour against space volume, target temperature rise and air exchange; the catalog classes run Up to 50k, 50-150k, 150-400k and 400k BTU +. Every selection carries a ventilation check — the size that heats the space must also have the fresh-air openings the manual requires.
Applications
- Heating open and well-ventilated construction areas
- Concrete curing and ground thaw support
- Tent and temporary structure heat with ducted fresh air
- Garage, shop and industrial bay heating with fixed unit heaters
- Spot heat for crews in unenclosed structures
Safety & operation
- Combustion products enter the heated space: carbon monoxide exposure is the class's defining hazard, and ventilation per the manufacturer and OSHA 1926.154 is mandatory, with CO monitoring in enclosed work.
- Clearances to combustibles are maintained per the data plate; tarps and tent fabric near discharge are recurrent fire causes.
- Propane cylinders and hoses are handled, secured and leak-checked per NFPA 58.
- Direct fired units are excluded from sleeping areas and tightly sealed occupied spaces outright.
Standards & certifications
- OSHA · 29 CFR 1926.154
- Temporary heating devices — ventilation, clearance and placement rules.
- ANSI · Z83.7 / CSA 2.14
- Gas-fired construction heater standard.
- NFPA · 58
- Liquefied petroleum gas code for propane supply and cylinders.
Frequently asked
Direct fired or indirect fired — how is the choice made?
How much ventilation does a direct fired heater need?
Why does moisture appear on cold surfaces near these heaters?
Compare popular models
Find by spec →Normalised to the same units. A dash means the figure was not published.
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| Multiquip GBHM | - | - |
| Val6 Hotgun 125NA | 636 cfm | 14.3 gal |
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Sources
Every specification is verified against the manufacturer's published data, with the source linked for reference.
All models
142 models · Page 1 of 3 · Every spec cited to source
