Please fill in the inputs below. Your result will be calculated and shown instantly in both watts and BTUs. If you have more than one room then click the “Save Room Details” and the calculation will be saved in the left hand column. You may add another room to this by using the “New Entry” button. You can then print off these details by using the Print option. We advise that you get a second opinion from your heating engineer as calculations can differ in certain situations.