In order to determine the size of heat pump you need you should consider a variety of factors such as. . . local climate layout number and location of windows insulation number of people living in the home appliances that may generate heat In addition to the square footage of a home, these factors can impact the size of heat pump necessary. A general rule of thumb is that for every 500-600 square feet of conditioned floor area, you should install one ton of capacity. We highly recommend consulting a professional to determine what size heat pump is best for your space.