How to Calculate Furnace BTU by Square Feet
- 1). Determine the quality of your home's insulation as either high or low. If your home is new or you know that it is well insulated, rate it as high. If you live in an older home, have decidedly poor insulation or are unsure, consider it low.
- 2). Locate your position on a climate zone map. If you live in a blue area and have a high insulation rating, you need 45 BTUs of furnace strength per square foot. If your insulation is low, you need 50. In the green region you need either 40 or 45 BTUs per square foot, depending on your insulation quality. In yellow areas it's 35 or 40, in orange, 30 or 35, and in places colored red on the map, 25 for high insulation and 30 for low.
- 3). Measure your home's square footage by finding the length and width of each room, multiplying the two numbers and then adding the area of all rooms together. Multiply your BTU needs per square foot by the total area of your house to find the ideal BTU rating for your new furnace.
