Heating and cooling a 900-square-foot area is done with a HVAC system. HVAC stands for heating, ventilation and air conditioning. Each item helps to maintain a comfortable environment within a living area. The proper size HVAC system will depend on the size of the area, the structure of the building and where it is located. The size and power of an HVAC system is measured in BTUs. You can calculate the required BTUs for a particular location using a simple formula.
Multiply the square footage by 25. For a 900-square-foot area, 900 x 25 = 22,500.
Count the number of windows in the area and multiply by 1,000. For example, if the 900-square-foot home has 10 windows, 10 x 1,000 = 10,000.
Count the number of individuals who live in the location and multiply by 400. For example, if three individuals live in the house, 3 x 400 = 1,200.
Add the results from Steps 1, 2 and 3. In our example, 22,500 + 10,000 + 1,200 = 33,700.
Add 10 percent to the total if the building is in direct sunlight. Deduct 10 percent from the total for a building that is well shaded. Do not adjust the total for a building in equal sun and shade. In our example, a 900-square-foot building requires a 33,700-BTU heating system if it is located in an area where it receives equal amounts of sun and shade, 37,070 BTUs for a location in direct sun and 30,330 BTUs for a location in a well-shaded area.