This figure represents an estimate of the annual heat loss from the basement of a 30' X 50' house with 18" of wall exposed above ground. (heat loss increases rapidly as more basement wall is exposed.) The dotted vertical line represents the example house, located in central Michigan, rated at 7,500 heating degree days. The difference in basement heat loss between an Unfinished poured concrete basement and a PWF with R-11 insulation=38,200,000 BTU's.