Estimate how much heat your rooms require.

  1. Fill in the form below and click ‘Calculate’. This will show the minimum output requirement of the heater needed for the space you have specified.
  2. Add other rooms to your list, for example ground floor or top floor rooms.
  3. Click ‘view report’ to see our recommendation for the specific heater required.
  4. Adding subsequent rooms
    If you want to calculate for a number of rooms that are similar, but are perhaps on different floors for example – on the results page use the ‘COPY & AMEND’ feature to avoid having to input identical information again. If the room you wish to add is very different for example on a different site with different dimensions, then click the ADD ROOM button for a fresh start.

This calculator provides a guide to the heating requirements, for the details you input, based on the building regulations in force at the time the building was constructed.

The resulting calculations from this form should be treated as a guide and are not intended to replace a professionally prepared, detailed heat loss calculation.

Required fields are marked with an asterisk *.

Please see general notes for instructions.

Site details

Please see construction notes.


Please see area note.

General notes

  • Internal heat transfer between spaces of different temperatures are not included.
  • A 10% margin is included on the final room heat loss.
  • Air changes rates have been assumed that will allow for a selected emitter to recover temperature should a window be opened for a short period.

Construction notes

  • Construction dates generally reflect Building Regulation U values however for simplicity some worst case allowances have been carrried forward.
  • 2013 to Present U values are representative for commercial buildings and have been based on the domestic building allowance, assuming a reasonable whole build carbon balance was taken.
  • If an older building has been renovated please use the most recent date of renovation.

Area note

  • Only input areas for surfaces which have an external surface. For example, do not enter a floor when there is a room below; or a ceiling when there is a room above.