Although it’s a relatively clean fuel, propane is expensive and has been losing popularity for years. In the winter of 2006-07, some 6.5 million homes used it for primary heat; this winter, that number is down to 5.6 million, according to EIA estimates. The cost varies a lot by region. In the Midwest, heating a home with propane costs an average of only $1,534. In Maine, propane is replacing oil because it's cheaper to use.