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English: The most popular method used for determining wire to water efficiency for underfloor heating takes into consideration the efficiency of the water pump and losses in the pipe fittings that connect the pump. The method is important as it allows the underfloor heating engineer to evaluate the efficiency of the whole system. In scientific terms, wire to water efficiency is the energy that is passed on to the water used to heat the coils divided by the energy that is fed into the system.

For a single pump with constant speed, the formula to find wire-to-water efficiency would be:

WWE = Em x Ep x 100 (%)

where Em is motor efficiency and Ep is pump efficiency.

This WWE usually fluctuates between 30 and 90% depending on the size and technical abilities of the pump. Smaller pumps will usually have a lower wire to water efficiency. For big construction projects involving a sophisticated multi-level underfloor heating system with several water pumps, it may be necessary to be able to develop a system that switches pumps on and off as and when required. This approach would lead to significant savings in operation cost, which is, in most cases, the main reason for installing underfloor heating in the first place.