How to rate your underfloor wet heating system.

We are often asked how many kW (Kilowatts) are needed for a wet underfloor heating system, to enable customers to work out the right underfloor heating calculations for your electric flow boiler.

Thankfully, there is there is a fairly simple formula for the most popular type of installation and layout. The most popular type of installation comprises a standard pipe diameter  of 16mm and a standard spacing between the pipe runs of approximately 200mm.

Most underfloor heating installations are designed to operate at up to 55 degrees Celsius, but this may vary from floor to floor, depending on many factors such as type of floor, environment, etc.

The kW requirement calculation will also depend on the type of floor:

70w per m2 for timber suspended floors

100w per m2 for concrete floors

So, as an example, if you were looking to heat a wooden floor 6m x 4.5m (27m2) then you would simply multiply 27 (m2) x 70 (watts per m) = 1890. This is 1890w or 1.89kw.

If you had to do the underfloor heating calculations for providing an electric flow boiler for this example, it would be an entry level size, and in the case of a Trianco model it would be the Classic TRI2, which is rated at 2kW.

Perhaps you have to provide heat for an underfloor system in a screeded concrete floor which is covering an overall area of 52m2. So in this case you would use the 100w per m2 calculation:

52 (m2) x 100 (watts per m) = 5200. This is 5200w or 5.2kW.

A suitable flow boiler for this application could be the Amptec U601 for example.

We stock the entire range of Trianco and Heatrae Sadia Amptec boilers and associated accessories at Electrical Deals Direct, all with free delivery.

We hope this quick guide has been of some help, and should you need further advice, please call one of the team on 01934 253600 or drop us a line at