Propane BTU Calculator: How Much Propane Does a Heater Use?

Our Propane BTU Calculator tells you how much propane heaters and furnaces of different sizes use per hour / day / month when running at full capacity.

The first step is to know the heating capacity of your heater or furnace. It should be listed on the appliance or can be found online with a quick search of the unit’s model number. Sometimes the model number gives it away if you understand what you’re looking at. For example, the Goodman GMES960804CN furnace is 96% efficient and has BTU input of 80,000.

We start with the calculator, which is simple to use. It’s followed by a chart showing propane use for heaters of various sizes.

  • Pounds to Gallons: We’ll do some conversions below that allow you to figure out your propane use if you run your heater off a propane bottle sized in pounds instead of gallons.
  • BTU per Gallon of Propane: You might also be interested to know that the calculator factors in BTU per gallon of propane, which is 1 gallon = 91,452 BTUs.

Propane BTU Calculator

Our calculator is simple to use. Plug in the capacity of your heater or furnace, and it will tell you how much propane it uses.

Step 1: Input BTUs

Enter the rated size or capacity of your heater or furnace. And it’s the only step!

Propane BTU Calculator

The result given is the amount of propane the heater uses if it runs non-stop, which is often the case with a garage propane heater or one used in a similar space that isn’t fully insulated – hunting blind, fishing shanty, tent, camper, workshop, etc.

Input vs output: Input is the number of BTUs of heat created by the heater.

If you’re using a ventless heater like those listed in our Top Ventless Propane Heaters, you’ll get every BTU created blown or radiated to the space you’re heating.

If you use a vented heater like those in our Top Vented Propane Heaters Guide, then some of the heat is lost in the exhaust.

While BTU input vs output doesn’t factor into how many BTU per gallon of propane it will use, it is useful to know. If you have a vented 30,000 BTU heater that is 80% efficient, then 30K x .8 = 24,000 BTUs into the space you’re heating while 6,000 BTUs are lost.

Quick BTU Chart – How Much Propane Does a Heater Use?

Here’s an easy chart showing how much furnaces and heaters of various common sizes use. How much propane does a 30,000 BTU heater use? Check the chart!

There are a couple tips for using it below the chart.

How much propane does a heater or furnace use?

Input BTUsPropane Used Per HourPropane Used Per DayPropane Used Per Month
how much propane does a 20,000 btu heater use0.219 gallons5.25 gallons157.46 gallons
how much propane does a 30,000 btu heater use0.328 gallons7.87 gallons236.19 gallons
how much propane does a 40,000 btu heater use0.437 gallons10.50 gallons314.92 gallons
how much propane does a 60,000 btu heater use0.656 gallons15.75 gallons472.38 gallons
how much propane does a 80,000 btu heater use0.875 gallons20.99 gallons629.84 gallons

Tip 1: Is your heater’s capacity not on the chart? Use the numbers given to determine how much propane your heater or furnace uses, if the size isn’t there.

For example, a 90,000 BTU furnace uses 3 times as much as a 30,000 BTU unit, so 3 x .328 = .98 gallons per hour.

A 120,000 BTU furnace uses twice as much as a 60,000 unit, so 2 x .656 = 1.3 gallons.

Tip 2: Factor whether the unit runs all the time. And do the math – explained below. It will help you estimate how long the heater will run based on the size of the bottle or tank it is running off.

If you’re using a Mr. Heater Little Buddy without a thermostat, or similar, it runs all the time, hour after hour.

But if your unit has a thermostat, and it eventually brings the space up to the thermostat setting, it will shut off until the area cools and needs more heat.

Most furnaces in well-insulated homes should run three to six times per hour with cycles of 4-12 minutes. The longer the cycle, the fewer times it comes on. In short, on a 40-degree day, a furnace will run about 24-36 minutes per hour in a home with decent insulation.

You might just have to time your furnace’s cycles over the course of an hour or two to get a true feel for how much it runs per hour.

Then you’ll have some math to do. Divide how long it runs in a typical hour, if there is such a thing, by 60 to determine the percentage of an hour it runs.

And then multiply that number by the BTUs per hour a heater or furnace its size uses. For example:

24 minutes / 60 = 40% or 0.40.

  • 40 x .656 = .262 gallons per hour.
  • 40 x 15.75 = 6.3 gallons per day.

Converting Propane Pounds to Gallons

Are you using a bottle of propane that is sized in pounds?

Your conversion is: 1 pound of propane = 236 gallons

Here are the pounds to gallons conversions for various bottle sizes.

  • 20 pounds = 4.72 gallons
  • 30 pounds = 7.08 gallons
  • 100 pounds = 23.6 gallons

These conversions are essential to determining how long your propane heater will run when your propane is in a bottle, not in a tank that is filled by the gallon rather than the pound.

Tank Tip: If you have a propane tank, a pig as it is often called, that runs your propane furnace or heater, it should have a gauge on it. The gauge shows how many gallons of propane are in the tank.

Once you know that, you can do the math using our Propane BTU Calculator and the BTU Use Chart to make an estimate of how long your supply of propane will last. This can help you budget your propane use for the winter and anticipate when you’ll need a refill.

By the way, to do this in reverse:

  • 1 gallon of propane = 4.24 pounds of propane.

Know What You’re Doing – Safe Use of a Propane Heater

BTU input vs output explained above might help you decide whether to go with a ventless unit or one that is vented. Just remember to follow all safety instructions given with a ventless propane heater to ensure there isn’t a buildup of exhaust gases in the space. Those gases contain a small amount of carbon monoxide, and exposure to that poisonous gas can cause headache, nausea and even death.

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