Best 400,000 BTU Heaters for Large Spaces

Choosing A High-Capacity Heater can be critical for warehouses, large garages, construction sites, and outdoor work areas. This guide compares high-output propane and gas heaters most relevant to the search for a 400,000 BTU heater, plus several heavy-duty alternatives and accessories that address large-space heating needs.

Summary Table Of Selected Products

Product	Output / Type	Key Feature
MH400FAVT 400,000 BTU Forced Air Propane Heater – Thermostat Controlled	250,000 – 400,000 BTU / Propane Forced Air	Thermostat control, up to 10,000 sq. ft. coverage
Mr. Heater F260560 Big Maxx MHU80NG Natural Gas Unit Heater	80,000 BTU / Natural Gas Unit Heater	Ceiling/Wall mount unit for ~2,000 sq. ft.
Dura Heat LPC80 50-80,000 BTU Propane Convection Heater	50,000 – 80,000 BTU / Propane Convection	360° convection, variable output, no electricity required
Mr. Heater Propane Unit Heater 80,000 BTU/Hr. MHU80LP	80,000 BTU / Propane Unit Heater	Spark ignition, mounts with included brackets
Propane Torch Weed Burner Kit, 2,400,000 BTU High Output	Up To 2,400,000 BTU (torch peak) / Propane Torch	Dual-mode torch for industrial tasks (not space heating)

MH400FAVT 400,000 BTU Forced Air Propane Heater – Thermostat Controlled, Black

Check Price on Amazon

This unit is listed with a variable output range of 250,000 to 400,000 BTU per hour and is designed for use with propane gas. The manufacturer specifies coverage up to 10,000 square feet, which places it squarely in the heavy-duty forced-air category. Key features include a thermostat control option that can help regulate ambient temperature for large spaces.

Applications: large warehouses, construction sites, agricultural buildings, emergency heat for very large spaces. Forced-air distribution is effective for rapid warming but requires proper ventilation and safe propane setup. Installation considerations include fuel supply, clearance requirements, and secure mounting. The product is intended for professional or commercial applications where high BTU output is required.

Mr. Heater F260560 Big Maxx MHU80NG Natural Gas Unit Heater, 80,000 BTU, Black

Check Price on Amazon

The Big Maxx MHU80NG is a natural gas unit heater rated at 80,000 BTU, intended for coverage of roughly 2,000 square feet. The unit comes with mounting brackets and is suitable for ceiling or wall installation. Note that thermostat, hose, and regulator are not included with the base unit.

This model is a compact, vented unit heater that provides targeted heating for medium-to-large indoor spaces. It supports both category 1 vertical and category 3 horizontal venting, which affords flexibility for retrofit installations. Clearance requirements and proper venting are key safety factors to observe for natural gas units.

Dura Heat LPC80 50-80,000 BTU Propane (LP) Convection Heater, Gray

Check Price on Amazon

The Dura Heat LPC80 is a variable-output convection heater designed for propane operation with a range of 50,000 to 80,000 BTU. It provides 360-degree convection, which is useful for distributing warmth evenly in enclosed areas. The unit is capable of operating for extended periods on large propane cylinders and includes a piezo igniter for simple startup.

Convection heating is different from forced-air in that it warms the air more gradually and can maintain even ambient temperatures without a blower. This model is suitable where quieter, steady heating is desired and where electrical power may not be available, as it does not require electricity for basic operation.

Mr. Heater Propane Unit Heater 80,000 BTU/Hr. MHU80LP

Check Price on Amazon

The MHU80LP is a propane-powered unit heater rated at 80,000 BTU, designed to heat areas up to about 1,000 square feet depending on insulation and ambient conditions. It features spark ignition and a self-diagnostic control module for easier troubleshooting during installation or operation. Two angle brackets are included for ceiling mount installations.

Unit heaters like this are commonly used in smaller warehouses, workshops, and garages. They deliver concentrated heat and are often installed near areas that need direct warm air flow. Proper clearances, fuel connection, and venting must be followed to ensure safe operation.

Propane Torch Weed Burner Kit, 2,400,000 BTU High Output with Long/Short Mode

Check Price on Amazon

This torch kit advertises a very high peak output (up to 2,400,000 BTU) for focused tasks like weed control, asphalt work, snow/ice melting, and roofing. It features interchangeable length sections, a CGA600 connector for multiple cylinder sizes, and a turbo trigger with self-igniter.

Important distinction: while the torch delivers intense localized heat, it is not designed for sustained space heating or occupant comfort. It’s an industrial tool for surface heating and removal tasks. Safety protocols, appropriate propane tank selection, and proper PPE are essential when using high-output torches.

Buying Guide: How To Choose A High-BTU Heater

Selecting a heater in the high-BTU range requires assessing fuel type, delivery method, use case, installation, and safety. Below are the main considerations to evaluate from several comparison perspectives.

1. Define The Heating Objective

• Space Heating (Ambient Comfort): For continuous warming of large enclosed areas, consider forced-air or unit heaters with thermostats and ducting options.
• Task/Spot Heating: Use directed heaters or torches for temporary localized heat; these are not substitutes for whole-space heating.
• Emergency/Temporary Jobsite Heat: Portable forced-air propane heaters can deliver rapid heat but require ventilation and safe fuel handling.

2. BTU Rating Vs. Real-World Needs

• BTU is a measure of heat output, but coverage depends on insulation, ceiling height, and heat loss. A 400,000 BTU rating indicates maximum output; it does not guarantee uniform distribution.
• Smaller units (50k–80k BTU) may be sufficient for moderately sized garages or workshops; larger ratings serve warehouses and open structures.

3. Fuel Type: Propane, Natural Gas, Or Electric

• Propane: High portability and high BTU options available. Requires safe tank setup and ventilation.
• Natural Gas: Lower operating costs when a gas line is available; venting and gas plumbing must meet code.
• Electric: Limited maximum BTU compared to gas; suitable for lower-output needs or indoor-safe environments.

4. Heat Delivery Method

• Forced-Air Heaters: Rapid heating and good for large open spaces; may create drafts and require fresh-air makeup.
• Convection Heaters: Even, quieter heat with slower ramp-up; useful where sustained ambient comfort is desired.
• Infrared/Direct Heat: Effective for spot heating of people and equipment without heating the entire volume.

5. Venting, Clearance, And Safety

• Confirm product-specific clearance distances and venting categories (e.g., category 1 vertical, category 3 horizontal) before installation.
• Install carbon monoxide detectors and maintain adequate fresh-air intake for combustion heaters in enclosed spaces.
• Follow local codes and manufacturer installation instructions for gas connections and mounting hardware.

6. Controls, Thermostats, And Efficiency

• Thermostat-controlled units provide better temperature regulation and can reduce fuel consumption. The MH400FAVT lists thermostat capability for automatic control.
• Look for models with variable output settings to match load and reduce cycling losses.

7. Portability And Installation Requirements

• Consider whether the heater will be permanently mounted or moved between sites. Permanent natural gas units may require professional gas plumbing.
• Check included mounting hardware. Several unit heaters include angle brackets to simplify ceiling installation.

8. Duty Cycle, Runtime, And Fuel Supply

• For propane heaters, calculate runtime based on cylinder capacity and BTU draw. Some convection heaters specify hours of operation on large cylinders.
• High-capacity units draw large volumes of fuel—ensure reliable supply and safe storage of cylinders.

9. Application-Specific Considerations

• Construction Sites: Forced-air propane heaters can warm large temporary shelters but require ventilation, placement away from combustible materials, and regular supervision.
• Warehouses/Industrial: Ceiling-mounted unit heaters may be preferred for even distribution and to keep floor areas clear.
• Outdoor Tasks: Torches are suitable for melting and surface treatment but are not a replacement for ambient heating solutions.

10. Maintenance And Serviceability

• Factor in filter access, ignition systems (piezo vs. electric spark), and availability of replacement parts and service technicians.
• Annual inspection of fuel lines, burners, and venting systems is recommended for safety and efficiency.

Comparison Perspectives: When comparing models, weigh peak BTU output against practical distribution method, installation complexity, and fuel logistics. A 400,000 BTU forced-air heater provides unmatched raw heat for very large spaces, but smaller unit heaters or convection models may be more appropriate for enclosed buildings with moderate volume or where quieter, sustained heating is desired. Torches and specialized burners deliver intense localized heat for industrial tasks, not occupancy comfort.

Regulatory & Safety Reminder: Always follow manufacturer instructions, local building codes, and fuel regulations when installing or operating combustion heaters. Use appropriate detectors and provide ventilation to mitigate combustion byproducts.