3 Ways To Calculate Btu Per Square Foot

For a rectangular room, multiply the length and width, measured in feet. [1] X Research source For a triangular room, multiply the length and width, then divide by 2. For a circular room, measure the radius (“r” which is the distance from the center to the edge). Plug the radius into the following equation, using 3. 14 for π: πr2 For rooms with odd shapes, divide them into regular shapes and measure each shape separately. If the room is not rectangular, you can try to break it up into rectangles so that you can calculate several lengths times widths. [2] X Research source For example, if your room is L shaped, break that up into two non-overlapping rectangles. Then calculate length times width for both rectangles and add them up. [3] X Research source

For instance, if you live in Zone 2 and have a 1,200-square-foot home, multiply 1,200 by 35-40 to get a BTU range of 42,000-48,000.

Say that you live in a brand new home in Zone 1. Multiply your square footage by 30 BTUs to find out what capacity furnace you need. Alternatively, if you live in an older home in Zone 6, multiply your square footage by 60 BTUs to ensure you purchase a furnace with enough capacity to heat the space. Note that newer homes tend to be better insulated than older homes because of revisions to building codes over the years.

For example, a 100,000 BTU/h input furnace would not be enough to heat a home needing an output of 100,000 BTUs per hour. An 80% efficient furnace would deliver an output of only 80,000 BTU/h (100,000 x 0. 8). To find an 80% efficient furnace that does provide enough power, divide the BTU/h rating you need by 0. 8. So, 100,000 BTU/h ÷ 0. 8 = 125,000 BTU/h, meaning you’d need a furnace rated to 125,000 BTU/h input.

Multiply the length by the width, in feet, to find the square footage of a rectangular room. Multiply the length and width of a triangular room, then divide that number by 2 for a triangular room. Measure the radius of a circular room (“r” which is the distance from the center to the edge), square the number, then multiply that by π (3. 14) (the formula is: πr2). Divide rooms with odd shapes or alcoves into regular shapes and measure each shape separately.

For instance, if you live in a home that’s 800 square feet, you’ll need a unit with 16,000 BTUs. On the other hand, if you live in a 5,000-square-foot home, get a unit with 100,000 BTUs.

Take a look at your sun exposure during the middle of the day in the summer season to help you gauge this accurately.

For instance, if there are 6 people living in your home, multiply 600 by 4 to get 2,400. Add 2,400 BTUs to the number you calculated by multiplying your square footage by 20 to ensure your unit will cool your space well.

For example, take a 4,000 BTU/hour air conditioner run for 1,000 hours during an operating year using 400,000 watt-hours of electric power. This air conditioner would have a SEER rating of 10, since 4,000 x 1,000 / 400,000 = 10. To find the average power consumption, divide the unit’s power in BTUs per hour by the SEER rating. Since the SEER rating is in units of BTU per Watt-hour, your answer will be in terms of watts. In the example above, (4,000 BTU/h) / (10 BTU/Wh) = 400 W. Central air conditioners manufactured in the United States since January 2006 are required to have a SEER rating of at least 13, or 14 to be Energy Star qualified. Room air conditioners are currently exempt from this requirement; many have SEER ratings closer to 10.