How to calculate the heating load of a house

Written by michael butler
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How to calculate the heating load of a house
A window air conditioner might be enough to cool your house. (window air conditioner image by Aaron Kohr from

Before you purchase a new air conditioner for your home, you should calculate your home's heat load. This will make sure that the air conditioner you purchase is powerful enough to cool your home. Heat load represents the total amount of heat generated in your home. Sources of heat in your home include the sun, people, lights and any major appliances. According to Hvac-for-Beginners, you need an air conditioner capable of producing more cooling units than your home's heat load.

Skill level:


  1. 1

    Multiply the number of square feet in your house by 31.25, a constant in the formula. Write the result down.

  2. 2

    Measure the length of all the north-facing windows in your home in meters and add them all together. Do the same for the width of all the north-facing windows. Multiply the two numbers together. If the north-facing windows are normally covered with drapes or blinds, multiply by 164. If they are not normally covered, multiply by 1.4. Repeat this process for all the south-facing windows in your house. Add the results from the north- and south-facing windows together and write the number down.

  3. 3

    Multiply the number of people living in your house by 600. Write the result down.

  4. 4

    Read the manuals or the stickers on the sides of all major appliances in your home, such as computers, ovens, microwaves, washers and dryers. Determine the number watts for each appliance and add them all together. Multiply the result by 3.4 and write it down.

  5. 5

    Calculate the total wattage of all the lights in your home and multiply it by 4.25. Write this number down.

  6. 6

    Add all of the numbers you wrote down. The result is the total heat load of your house.

Tips and warnings

  • Plumbers and heating and cooling installers are trained to estimate a home's heat load. They are both excellent resources in determining your home's air-conditioning capacity needs.

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