The bare minimum is one free-standing patio heater for every 1,500 square feet of space. So, if you have a 500-square-foot patio, you'll need one. If your patio size is 3,000 square feet, you'll require two patio heaters; and so on. Since this is for domestic use, you could likely increase the number based on the fact that you will probably hire your patio heaters rather than buy them.