With the growing need to improve the energy efficiency of existing commercial properties, the retrofit market for underfloor heating (UFH) has a bright future, says Mark Millett

Underfloor heating in retrofit applications is a practical solution for commercial buildings such as those with high ceilings that are using inefficient, noisy hot air duct systems. Although not appropriate for every building, if there is sufficient insulation, UFH is viable and will improve performance, acoustics and comfort levels.

Claims that water-based UFH can be up to 30 per cent cheaper to run than conventional radiators make the system an even more attractive solution when old systems are being replaced.

Standard floor constructions
Of the three standard floor constructions available - floating floor, suspended timber and screed - suspended timber floors have little impact on floor height build-up, although ceilings or floors will have to be removed in order to lay the floor heating tube. This is acceptable if they are being replaced anyway, but if they have to remain in-situ a floating floor is a better solution.

The floating floor construction is a popular option for retrofitting UFH due to minimal floor height build-up and straightforward installation, as it is laid over the existing deck. An average floor height build-up of 150mm means that screed is better suited to renovation projects where floors are being removed or sufficient height is available.

The choice of floor covering is as important in a commercial building as it is in a domestic property. The best results are obtained from stone, marble, ceramic tiles and polished screed. These all conduct heat well and present little barrier to the even dispersal of warmth. Thick flagstones will take a little longer to reach the right temperature, but the heat emitted will be the same as with thinner stone. Using carpet is feasible as long as the TOG value (including the underlay) doesn't exceed 2.5 and ideally is less than 1.5.

Most efficient underlay
Waffle-backed foam underlay is likely to be the most efficient choice of underlay. If timber flooring is used, it should be recommended for use with underfloor heating and must be well-seasoned or kiln dried. Although the lower operating temperature of underfloor heating means that most solid timbers can be used, there are also advantages to using engineered boards instead.

First, the cross ply gives better stability. Secondly, because only the top surface is visible, the main constituent timber can be a more stable material (with a higher contact temperature).

Underfloor heating is the perfect partner for all types of heat source, including condensing boilers and renewable technologies, helping to achieve maximum efficiency. When airtightness in commercial properties reaches the appropriate levels, UFH can be integrated with a heat pump. Key to the specification of an integrated system is the correct sizing of the heat pump.

The author is product manager at Nu-Heat UK