I currently has a propane gas patio heater. Its design allows a massive amount of heat to escape upward instead of being reflected downward due to its use of combustion to produce heat.

I would like to replace the unit with a soffit mounted linear electric heater. You can see a picture of both the current heater and the spot where I would mount under the soffit below:

Existing conditions

The gas unit is rated at 42,000 BTU/hr. However, clearly it loses a lot of its heat as convection away from the unit since much of the heat produced is combustion products rather than infrared that is reflected back at me.

What wattage electric model (which presumably is more efficient in producing infrared rather than heating the air) would best replace the existing unit?

  • 2
    Old question, I know, but if that's vinyl siding/soffit and you're planning on adding a huge amount of heat there, heat & plastic tend to not mix well. Heat may also significantly shorten the lifespan of paint on any non-vinyl type siding (wood, cement board, etc.)
    – FreeMan
    Commented Jun 4, 2020 at 13:27

1 Answer 1


42000 BTU/hr would be about 12.3 kW/hr. The best way is to replace the heater with a one or more infra red heaters up to the required amount of heat you need. If you place more heaters you could position them on different spots. Only where required. I would start with 4 units of 1500 W and then see where you arrive.

Please keep in mind that you should seperate the heaters over different groups. This to prevent to problems with your breakers and wiring.

  • You can't convert 42,000 BTU/hr directly to 12,300W because of the significant differences in efficiency between the two units. The electric ones will be substantially more efficient. Commented Apr 22, 2017 at 15:03
  • Watt to BTU conversion factor is 3.41214........ ; efficiency has nothing to do with it. Commented Feb 3, 2020 at 16:57
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    @blacksmith37 No, that's not correct. If the electric heater is 100% efficient and the gas one is 0.00001% efficient, you would feel no heat from the gas one and plenty from the electric one. Efficiency has everything to do with it. Commented Jun 5, 2020 at 16:17
  • You are confusing location and the reflector design with efficiency. Commented Mar 8, 2021 at 15:54
  • @DavidPfeffer. BTU/hr and kW/hr refers to the energy output of the units. The input units or energy required to obtain the output is always higher. The difference between input and output reflects the efficiency
    – Decapod
    Commented Mar 10, 2021 at 7:06

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