How Many BTU Heater Does It Takes to Heat Your Tent?

This is a back of the envelope method that you can use to roughly estimate how many BTUs of Coleman heater you might need to heat a tent, an ice shack, or a garage to a reasonably comfortable temperature.

We'll start with the variables of the basic BTU formula and then toss out a few fudge factors that you will have to guess at based on any particular situation. The calculations will be reasonably accurate so long as the tent or other enclosure that you want to heat up is adequately shielded from the wind. No estimate is going to be effective if a freezing wind is blowing your portable heater off the table.

We'll use an ice shack for our first example because the enclosed area is a neat rectangle which makes the math part very straightforward. Further down we'll do the same calculations for a tent, which takes a couple extra steps because very few camping tents are pure rectangles like our ice shack example.

We'll set the dimensions for the ice shack at 8' x 8' with an 8 foot ceiling. The ceiling is probably a bit high but the dimensions fit nicely for an ice shack made with whole sheets of 4 x 8 plywood.

Step One: Calculate the square footage of the floor area. For our ice shack we multiply 8 x 8 and come up with 64 square feet.

Step Two: Calculate the cubic feet of the enclosure by multiplying the number we got in Step One by the height of the ceiling. 64 x 8 = 512 cubic feet.

Step Three: Select a Fudge Factor. For an enclosure as well insulated as a house the Fudge Factor is 2. For a poorly insulated enclosure the Fudge Factor is 4.

These Fudge Factor numbers are arbitrary. I know. But they're still useful to get you in the ballpark. If you had a poorly insulated ice shack in -5 F weather with two miles of wind fetch maybe you'd want to use a Fudge Factor of 7 or 8.

The other big arbitrary variable is how warm is 'warm.' For some people warm means toasty enough to wear a T shirt. For our purposes here let's call 'warm' enough heat to keep your fingers supple and in perfect working condition without blowing on your hands every few minutes.

For our ice shack example we'll use a Fudge Factor of 4. Our ice fisherman was generous with his foam insulation. 4 x 512 = 2,048 BTU.

Now we know that if our ice fisherman brings along a portable propane heater with 2,000 BTU output that he will stay reasonably comfortable in his ice shack.

Tents are more complicated because you have to do two separate volume calculations and then add them together because most tents are a combination of a rectangle and a triangle, or a cone.

Here's our example tent dimensions. 10 x 8 ft. floor area with a 5 ft. ceiling height in the middle. The walls of the tent are perfectly vertical for 3 ft and then slope toward the center.

First do the rectangle calculation for the floor area: 10 x 8 = 80 Sq. Ft.

Next do the cubic feet calculation for the rectangle area: 80 x 3 = 240 Cubic Feet.

For the ceiling part of the tent we use the volume calculation for a cone which is: Sq. Ft. Area of Base x 1/3 x Height.

For our tent that works out to (10 x 8)/3 = 26.67 multipled by the Height of 2 ft, which looks like this: 26.27 x 2 = 53.33 Cubic Feet. (Multiplying by 1/3 is the same as dividng by 3).

Add the rectangle and cone volume calculations together: 240 + 53.33 = 293 cubic feet.

We finish off the tent calculation by multiplying the volume by a Fudge Factor. Instead of using the amount of insulation use the outside temperature. Fudge Factor 4 for 'chilly' outside temperature up to 7 or 8 for really cold weather.

We arbitrarily select 5 as a Fudge Factor. Multiply the tent volume of 293 cubic feet by 5 to get 1,465 BTU.

If you won't remember any of the math then just read the volume of the enclosure in cubic feet off the product description and multiply it times 4 and you'll be somewhere in the ballpark when buying a portable propane heater.