How to Figure the Size of a Heater Air Conditioner for a House

How to Figure the Size of a Heater Air Conditioner for a House thumbnail
Ensure you have the air conditioner and heating unit that's right for your house by calculating the proper size needed before purchase.

Before you purchase a heater or air conditioner for your house, you need to know the size of the unit you should purchase. Determining the necessary size for a heater or air conditioner is a complicated process. Though the size is ultimately determined by the space being affected by the unit, other factors, from the general climate of the region in which you live to the number of windows in your home, as well as the number of occupants, all play a part. Because of this, consider utilizing one of the many software applications available through retail sales or online to help you in making a final determination.

Things You'll Need

  • Heating, cooling and air software application
Show More


    • 1

      Obtain a software application to assist you in figuring out the size of the heating and air conditioning unit required for your house. While there are sever available through retail sources, one of the more comprehensive applications is the online worksheet listed in the Resources section below. Log onto the site, and input the necessary information to figure out your needs.

    • 2

      Use a tape measure to measure the length of the walls in your house, both inside and out. You’ll need to split the outside measurement between those walls that receive direct sunlight and those that do not. Measure only one side of the interior walls, and then add all the interior wall measurements together. Place these measurements into the worksheet, along with the type of insulated construction the frame of your house employs. All measurements should be in feet, rounded up to the nearest foot for the best results.

    • 3

      Measure your ceiling with the tape measure, taking both the height of the ceiling and the ceiling area as determined by multiplying the ceiling length by its width. If your home is not a complete square, then break the structure down into squared sections and take the area for each. Add the sections together and use the results for the worksheet, as well as the type of insulation installed above your ceiling. If you aren’t sure of the insulation type, then check the attic or open the access panel leading to the crawlspace beneath your roof to determine the type of insulation that’s been installed, if any.

    • 4

      Use the tape measure to determine the floor area of your home, and then place the result into the worksheet. Use the same area measurement process that you used with the roof.

    • 5

      Measure each window in inches and divide the result by 144 to calculate the window’s square footage. Mark down the direction that each window faces, along with the type of windowpane and whether a shade is present. Add up the areas for each of the eight directions, and then place the information gathered into the worksheet.

    • 6

      Count the number of people normally occupying the house and place the number in the worksheet, as each person gives off heat.

    • 7

      Check over the data entered, and then press the calculate button to determine the number of BTU/hour your heating and air conditioning unit will need to handle. Purchase a unit that’s at least this amount to ensure that it can handle your house’s environmental needs.

Related Searches


  • Photo Credit Comstock/Comstock/Getty Images

Related Ads