To Calculate Heat Requirement for Your Room A good rule of thumb guide to calculate the heat requirement of a given room is: IMPERIAL Height x Width x Depth (in feet) divided by 500 METRIC Height x Width x Depth (in metres) divided by 14 This gives you the kilowatt requirement. DEFRA APPROVED The clean air act of 1993 authorised Edinburgh’s local authorities to designate Edinburgh a smoke controlled area, and this has remained in place to this day. This means it is illegal to burn ordinary coal (rather than smokeless fuel) or wood in the Edinburgh area. Wood can only be burned in stoves that have been tested for their use in smoke controlled areas and are exempt from the regulations by being DEFRA (Department for Environment Food and Rural Affairs) approved. Look for this (tree) symbol alongside the stove entry if you are in Edinburgh and want to burn wood in your stove. On every Defra approved stove you’ll see this symbol. This symbol demonstrates the stove output in kilowatts.