This is a widely used and relatively quick method, but the result is not very accurate. The printer friendly spreadsheet is here: Whole House calc v1.1.xlsx
MCS compilant method
If you want to apply for BUS Grant to install a biomass heating system, you will need a heatloss calculation to determine the capacity of the required heat source (boiler/stove). If you fill in this form, I will complete it for you. The calculation will not be just informative, but it will be MCS compilant. Alternatively please fill in the printer friendly spreadsheet version, the Heatloss data 4.1 blank.xlsx file. Please note this is a free service. But filling in the form may be time consuming.