Unit heaters are a very basic and affordable way to provide heat to spaces that might not be heated otherwise. Garages, barns, shops, greenhouses, etc. are all examples spaces that can benefit from the versatility of a unit heater.
Figuring out how large of a unit heater you need is quite simple. (This is really the bare bones version of BTU equations. These numbers are good for estimating but are not exact.)
Cubic Footage x Insulation Factor = BTU required
Cubic footage is simply Length x Width x Height.
The insulation factors are as follows:
4.0 - good insulation
5.0 - average insulation
7.0 - poor insulation
Generally it’s better to ere on the side of caution and oversize a unit heater for your particular space. Also, be sure to account for large windows or doors that don’t have matching insulation values.
A pole barn with the following dimensions and insulation
Ceiling height 12’
Insulation – Average
The BTU to heat this building would be as follows:
60 x 40 x 12 x 5.0 = 144,000 (BTU required)
The best unit heater for this space would be a UH-140 (158,000 BTU).