How Many Btu to Heat a Square Foot?

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You may have heard the term Btu when it comes to home heating. This unit of measurement, short for British Thermal Unit, is used to rate how much energy it takes to produce heat. It's often used in determining the efficiency of appliances that cool or heat. Depending on where you live, you will need different Btu levels to properly heat your home. Fortunately, there is a standard rule of thumb for Btu needs per square foot, sorted by climate zone.


How Many Btu to Heat a Square Foot?
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What is a Btu?

Technically speaking, a Btu is equal to the amount of energy required to raise 1 pound of water 1 degree Fahrenheit. Often, particularly in North America, the term is used to describe the heating power of fuels and appliances. In this capacity, when the term is used, it usually means Btu per hour. You may also see the term MMBtu used. This means 1 million British Thermal Units.


How to Determine the Btu You Need

Depending on your region, you may need a different Btu per square foot in your home to keep it at a comfortable temperature. In climate zone 1, which occupies much of the southern part of the United States and parts of Arizona, Nevada, New Mexico and California, you should have 30 to 35 Btu per square foot of home. In climate zone 2, located just above climate zone 1 and stretching from the Carolinas to much of California, you should allow 35 to 40 Btu per square foot. In climate zone 3, covering the middle portion of the United States and parts of Arizona, California and Oregon, 40 to 45 Btu per square foot is required. In climate zone 4, which begins in Massachusetts and stretches across the country to parts of Oregon and Washington, you'll need 45 to 50 Btu per square foot. Finally, climate zone 5, which spans the northern part of the nation, calls for about 50 to 60 Btu per square foot of heatable space.


How to Convert Btu to Therms

When you receive your natural gas bill, it most likely will not use Btu as a unit of measurement. Instead, natural gas may be priced as dollars per therm. One therm is equal to 100,000 Btu or 0.10 MMBtu, while 100 cubic feet of natural gas equals 103,700 Btu or 1.037 therms. Therefore, the price per 100 cubic feet divided by 1.037 is equal to the price per therm.


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