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BTUs: What They Are and Why You Should Care

Man in his home accessing the British Thermal Unit
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What you need to know about this puzzling number and how it can help you select the most energy-efficient appliances to heat and cool your home.

We’ll admit it. When it comes to propane and home heating equipment, there’s a lot to learn. And propane geeks like us don’t always make it easier. We use jargon and numbers and letters that are Greek to most sensible people. One of those terms is (dun, dun, dunnnn...) BTU.

What does BTU stand for? Here we’ll explain what that number on the side of your furnace and other appliances means and how it can help you decide how to heat your home for max comfort and efficiency. (There are many factors that go into energy efficiency calculations, and other corresponding information on your appliances, but in this article we’ll focus specifically on BTUs.)

What’s a BTU?

A British thermal unit (BTU) is one way heat is measured. Now, you may be asking: Wait, isn’t heat measured in degrees? And you’d be right: The temperature of an object or in a space -- how warm or cold it feels -- is measured in degrees (Fahrenheit or Celsius, depending on where you live). However, BTU tells us something a little more specific. And frankly, it’s a little mind-blowing.

If temperature tells us how hot something is, like air or water, BTU tells us how much heat is needed to change the temperature. A BTU is what we get when we take the physical experience of getting warmer and express it in actual things you can count.

(Is your head exploding yet?)

OK, quick physics lesson: Say you have a pound of water, and it’s about 39 degrees Fahrenheit. (Side note: There’s a science-y reason to start at 39, but we won’t get into that here.) And you want to add enough heat to that water to get it up to 40 degrees. How many “units of heat” do you add to the water used to make that happen? That is equal to 1 BTU.

(To give you a visual, 1 BTU is about the same as burning a match. Compared to heating your whole house, it’s pretty tiny.)

BTU compares fuel types

One tricky thing about fuel types is that they’re all delivered differently and use energy differently. Natural gas is measured in cubic feet; liquid propane is typically measured in gallons. Because BTUs tell us how much energy is used, regardless of its form, it gives us a way to compare fuel sources. For example:


1 kilowatt-hour = 3,412 BTU

Natural gas

1 Ccf (100 cubic feet) = 1 137,000 BTU

Heating oil

1 gallon = 138,500 BTU


1 gallon = 91,452 BTU

The higher the BTU per unit of fuel, the more efficiently you can heat a given space. Translation: You get a lot more oomph from a gallon of propane or heating oil than you do from a cubic foot of natural gas.

Now, you might look at that table and think: Heating oil is the clear winner because it gets so many BTUs per gallon. That’s where the next factor comes in: the cost of fuel. That’s the other way in which BTU lets us compare apples to apples. It tells you not how much product you get per dollar, but how much energy you get per dollar. Here’s the quick math:

According to the US Energy Information Administration, as of February 2021…

1 Ccf of natural gas yields about 137,000 BTU and will cost you $0.955

1 gallon of heating oil yields 138,500 BTU and will cost you $2.75

1 gallon of propane yields 91,451 BTU and will cost you $2.304

In the end, you can see that propane yields 47,048 fewer BTUs per gallon than heating oil. But consider a few other factors: Propane is $.446 cheaper per gallon than heating oil; it also can be delivered to your home through a supplier of your choice. 

BTUs help you make home heating decisions

It’s good to know some basics of how BTU is calculated; now we need to answer another critical question: How many BTUs do you need to heat your home? Well, extend that “1 degree, 1 BTU” formula out to an entire home. How many “energy units” do you need to raise the temperature of your living room 1 degree, from 65 to 66 degrees? Or, in winter, from 0 degrees all the way to 70?

Imagine a spacious living area -- say, 12 x 18, with a 9-foot ceiling. Assuming your insulation is up to the latest standards, to heat that room from 0 to 70 degrees in the winter, you’d need 12,700 BTU. Per hour. That knowledge can then guide your decisions about the most reliable, efficient appliances and fuel type for your needs. Remember: It’s not as simple as asking “How many BTUs per square foot?” You’ll need to base any calculations on cubic feet to account for the volume of air in the room, not just the area.    

Here’s a rule of thumb for fuel shopping: Get the BTU # that best fits the space you're heating - without going over. 200K BTU isn't helping you if you only need 120K, but if you need 120K and you get 100K, you're going to waste energy and be cold. Use a conversion tool like this one to estimate your needs, then call AmeriGas for advice specific to your situation.

You don’t have to become a certified propane geek to use BTUs to your advantage. With a little awareness, that huge number can be one key to creating your coziest, coolest, most cost-efficient home.



Still not sure? Learn more about how propane can fuel your home. 

Or, contact us We’re happy to help.

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If you want to get into the nitty-gritty with the numbers, geek out with us here.