Measure every room's length and width. Multiply each value to get the area of each room in square feet. Write the areas down for each room.
Add all the areas together to get the full area you intend to cool.
Multiply the full area by 25. This gives you the raw cooling capacity necessary for the house, not accounting for other things that might affect your calculation.
Count all the windows in your house and add 1000 to your previous number for each window.
Determine the average number of occupants your house should hold. If you live alone, you count as one occupant. Add 400 for each occupant. The final number determines the HVAC capacity you need, measured in British thermal units (BTUs).
- Don't confuse BTU capacity with horsepower. The horsepower measurement points to how much power the blower motor has.