Yes that is a good way to calculate the heat loss. The site will still show you the cost difference per kWh of heat without the heat loss. Since heat loss is

Yes that is a good way to calculate the heat loss. The site will still show you the cost difference per kWh of heat without the heat loss. Since heat loss is the amount of heat the house loses per hour, and you have how much fuel it took to heat your house, you only need to reduce the amount of fuel consumed by the amount of fuel you lost when heating. For example if your furnace is 95% efficient than you need to reduce that number by 5%, since 5% of the fuel didn't end up heating your house. Divide this new number by the amount of heating hours and that will be your heat loss.