Underfloor heating: your questions answered

Thinking of installing underfloor heating? Real Homes has posed your most-asked UFH questions to industry experts

Wet vs dry systems

As electric systems are installed directly under the floor covering, and work independently from your central heating system, they are particularly useful for one-room installations or where the sub-floor level is already set. The wire or matting systems are very thin (around 3mm) and shouldn’t cause problems with differing floor levels – thus creating little disruption to the existing room.

Wet systems circulate warm water through plastic pipes installed underneath the floor and are connected to the main central heating source. This system tends to work best when the pipes are embedded in a screed, as this helps dissipate the heat, so it is suited to new floor constructions where the sub-floor can accommodate the pipework and cement screed. Wet systems are therefore more likely to be used in new-builds and extensions or during major renovation work.

Ease of control

Specialist UFH controls are vital to ensure comfort, responsiveness and energy efficiency. UFH takes longer to heat up and cool down compared to radiators, so to overcome this time lag, programmable controls are essential.

For households with irregular or limited occupancy and for holiday homes, it is useful to have remote control so that you can turn it on an hour or two before arriving. Remote control is also useful if you forget to turn the heating off.

Getting the right insulation

Underfloor heating will always be more efficient and cost-effective when fitted above insulation, as this reduces downward heat loss and forces heat up into the room where it is wanted. In new-build homes and extensions, floor insulation will be incorporated to meet Building Regulations, while on refurbishment projects insulation can usually be added.

Taking up existing floorboards to add insulation between the joists is fairly straightforward. Adding insulation to a concrete screed floor, however, will mean that the height of the floor is increased so skirting boards and doors will have to be adjusted accordingly. We always recommend speaking to a reputable company, as they will be able to offer advice based on the individual characteristics of your home.

Choosing flooring

Solid floors, including stone, porcelain, ceramic, terracotta and slate are ideal, as they tend to have great thermal conductivity and will provide good heat output when it comes to underfloor heating. If you prefer timber flooring, always check with your supplier to ensure it is suitable for use with underfloor heating, or consider engineered timber boards that, due to their construction, tend to be more stable during changes in temperature.’

In both cases, bear in mind that temperatures shouldn’t exceed 27°C. Most top-of-the-range laminates can also be used with underfloor heating, as can all carpets — although you may find heat output is slowed down a little, due to the combination of carpet and underlay.

Potential faults

The main cause for concern for many prospective buyers of warm water underfloor heating is what to do if the pipes leak. However, unless a nail is accidentally put through them at some stage, this simply does not happen. There are no joints in the floor and the various pipes used are designed and tested to have a 50-year life expectancy at temperatures and pressures that exceed those required by the system.

If accidental damage should occur, then individual pipes can be pressure tested to locate the correct one. In timber floors, the pipe can usually be exposed to allow for repairs, while screed floors will need to be excavated to uncover the pipe.

Choosing the right system

It’s particularly effective for large open-plan spaces – particularly those with high ceilings – as the entire floor radiates heat upwards so you benefit from warm feet and even room temperatures. This radiant heat also means reduced draughts, moisture levels and airborne allergens.

Typically underfloor heating is more than enough as a stand-alone form of heating. However, its capabilities will often be dictated by other factors, such as floor coverings and a building’s insulation levels (especially walls and windows). This is why heat-loss calculations are so fundamental, as having looked at a building’s individual thermal performance they will tell you how much heat you need to generate.

For example, a poorly insulated room with lots of glazing may not heat fully when it is cold outside (which means additional insulation or supplementary heating may be necessary). Floor coverings also play an important role. Normally, stone and tiles are excellent options, as are carpets with suitable tog ratings. If you’re keen on timber, however, remember it has a lower temperature tolerance.

Underfloor heating vs radiators

Where cost is an issue, the expense of installing underfloor heating may outweigh the advantages, especially if it involves removing concrete floors and re-screeding. In houses not occupied during the day, underfloor heating’s slow warm-up and cooling time (which can be up to four to six hours) may not suit you.

‘A combination of both systems can often be the best answer for many homes, as radiators can be easily incorporated into an underfloor system. A good compromise is to install underfloor heating on the ground floor, with radiators upstairs to accommodate the different requirements for living and sleeping spaces, especially as many people still want heated towel rails in their bathrooms.’