Heat Output Requirement Calculation

Using the below calculation tool you can easily deduct the requirements for most rooms. Note that towel warmers are not intended to replace like for like the performance of a panel radiator as they have much lower surface area and convection capabilities.

Once you have the figure required for each room, any combination of products and different sizes is possible until you achieve the required output figure.

Heat Output Calculator

Heat Output Calculator

What are BTU’s

BTUs are ‘British Thermal Units’, the unit in which radiator efficiency is measured. Factors such as room dimensions, windows and wall type are used to calculate the required outputs of radiators, in order to adequately heat a room.

How do I calculate the BTUs for my room?

Our BTU Calculator is an accurate guide as to what level of BTU and Watt output will efficiently heat your room. Please note: the calculated figure is for the combined heat output of all radiators and/or towel rails in your room (larger rooms may require more than one).

  • Dimensions of the Room Feet Meters
    Width: Length: Height:
  • Select the Room Type
    Dining Room/Lounge Bedroom/Bathroom Kitchen/ Common Area
  • Additional Factors to be taken into consideration. Does the room have:
    North Facing Wall French Windows Double Glazing

Manual Output Calculation


Multiply the room length in metres by the room width in metres by the room height in metres (LxWxH) to calculate the total cubic volume of the room.

Step 2

Multiply the room cubic volume by 45 to give you the Watt requirement.

Step 3

Combine all of the applicable correction factors from the list below and then apply the total percentage to the Watt requirement calculated in Step 2.

-25% Upstairs bedrooms

-20% Cavity filled walls

-10% Solid floor

-05% Double glazing

+10% Un-insulated cavity walls

+10% North facing wall

+15% Patio doors or French doors

+15% Two outside walls

+15% No loft insulation

+20% Ceiling height above 3 metres

+40% Three outside walls


Frequently Asked Questions


Electric Towel Rails

Central Heating Towel Rails

Convector Panel Radiators