Underfloor Heating

Heating by radiator has been the main option for new builds and refurbishments since the 1960s, when space heating became commonplace in Britain. Radiator-based central heating has a lot going for it. Its simple to install, easy to understand and widely available. Its also the cheapest option, provided you stick with standard pressed-steel radiators, found in 95% of homes.

However, radiator heating is not universally admired. Radiators are not always terribly attractive and they consume wall space that could be used for other things. They also create hot and cold spots in rooms: despite being called radiators, they work mostly by creating convection currents that drive air around a room, which in turn creates drafts.

In contrast, underfloor heating (UFH) works on a different principle. Whilst the radiator circulates the air around the room, UFH mostly radiates heat from the ground upwards, with very little air movement involved. Consequently, an UFH heated room is warmest down at your feet where it is said to be most comfortable. As the heat is mostly radiant, your body feels warm without being aware that the space is heated.

Installation Costs

As a rule, UFH is more expensive to install than standard radiators. Pressed-steel radiators are so cheap that several hundred metres of underfloor pipework struggles to compete on price. Additionally, the wall-mounted controls and numerous motorised valves add to the cost and complexity of the typical UFH system. Generally speaking, it probably adds between £1,000 and £2,000 to switch from radiators to underfloor. However, laying the pipe is not a particularly skilled job and many self-builders take this task on themselves, which greatly reduces the overall cost differential.

Running Costs

Proponents of UFH claim that it is significantly cheaper to run than radiators. The reasoning behind this claim is that UFH operates at lower temperatures than radiators and this, therefore, minimises heat loss through the fabric of the house and via the connecting pipework. On the other hand, UFH systems, particularly those fitted into screeds, are a slow-response heating method and heat may go to waste if the occupants are not around 24/7 to enjoy it.

You might think it would be easy to compare costs between similar houses fitted with different heating systems but this method throws up some highly erratic results, far more dependent on how individual families use their heating systems than on the technologies employed. On balance, it would seem that there probably isnt a lot to choose between UFH and radiators in energy-efficiency terms.

Responsiveness

One of the key differences between radiators and underfloor heating is the time taken to get a house warm. Radiators are quick, UFH is slow. UFH is particularly slow when you lay it in a heavy cement screed; when laid under a timber floor its much quicker. The question you have to decide is whether this matters. It depends a lot on your lifestyle. If your house lies empty ten hours a day and you frequently go off for weekend breaks or winter holidays, then you will probably find UFH a little unresponsive and will long for the simplicity of radiators. However, if you are around during the daytime and plan to keep the heating on most of the winter, then the slow response of UFH will not be an issue. The feedback from the majority of self-builders who have fitted UFH is that they love the type of heat delivered by UFH, particularly the warm floors, and that this more than offsets the occasionally slow response of the system.

Judicious use of heating controls is the answer. Most UFH systems run on a setback thermostat that keeps the system ticking over at a lower temperature during the night. As you are aiming to heat the entire structure of the house, the emphasis is on keeping a trickle of heat going all the time rather than short bursts of heat demanded by radiators.

Aesthetics

For many people, the absence of radiators is a big plus. The industry standard, pressed-steel radiators, are not exactly attractive; you can elect to buy some very fancy designer radiators instead, but these are expensive at least as expensive as fitting UFH.

Note, however, that UFH is not entirely hidden. The pipes emerge from the floor at a manifold, often about the size of a radiator and even more unsightly. It is normal to site the manifold in a cupboard or some other out-of-the-way spot where it wont cause visual intrusion.

Floor coverings

A well-designed UFH system should take floor coverings into account. Some coverings, notably wood and carpet, act as insulators and will reduce the amount of heat escaping through the floor. Typical outputs are 140w/m² under screed and tile, 105w/m² under vinyl tiles, 95w/m² under carpet and 75w/m² under timber and carpet. In a new house built to 2006 insulation standards, the maximum heat load shouldnt exceed 40w/m², so you can see that even the worst-case scenario still delivers adequate heat output. Generally, you can adjust the temperature of the water running through the pipes to account for such differences but what each individual circuit can't cope with is mixed floor coverings. So you really have to think about floor coverings at the outset and ensure that each pipe circuit only underlies just one type of floor cover.

UFH Under Timber Floors

One of the key concerns with UFH is that it may cause timber floors to move or even warp. It can happen, especially with solid timber floors. However, if you follow the manufacturers guidance, there shouldn't be any problems.

These last two points are good advice for anyone thinking of fitting a hardwood floor, whether there is UFH involved or not. The important points to bear in mind are that you must bring both the underlying screed and timber into equilibrium so that the moisture levels are in balance.

UFH Under Stone Floors

Ceramic or stone floors work particularly well with UFH because the warm floor effect works best when the floor cover itself conducts heat straight through. However, just as with timber floors, it is really important to let the screed dry right through before any cover is applied otherwise moisture will remain trapped in the screed and the floor may move. Large areas of screed, or passageway runs, over 8m in length, should be broken up with expansion strips.

Testing

One of the issues that people worry about is what happens if the system springs a leak. In fact, warm water UFH circuits are almost always laid using long lengths of pipe that dont have any subfloor joints, thus the commonest cause of leaks is neatly avoided. However, it is best to carry out pressure testing on any pipework before it is buried. Care also has to be taken to ensure the pipework isnt damaged when laying screed or fixing into the floor.

Specialist controls

All new heating systems require both time and temperature switching. UFH is no different but because it is split into separate heating zones instead of individual radiators, the controls tend to be greater in number. Each zone tends to be controlled by wall mounted thermostats and is switched on and off by a motorized valve. In contrast, a radiator-based heating system is often arranged in a single zone with each individual radiator controlled by simple thermostatic radiator valves. This can become an issue as regards future serviceability of the system. UFH remains the province of the specialist and if you buy your system from one of the reputable suppliers, they should keep all your system details for future reference. There arent many moving parts to go wrong, but thermostats, valves and pumps may well need attention after a few years in service. Though none of this work is out of the ordinary for a modern plumber, it can be time consuming for someone to find their way around a complex system and it can save a lot of time and expense if the nature of the work is already documented and understood.

Further Reading:

• The Death of Central Heating
• Heating Your Home
• Alternative Heating
• Underfloor Heating: Your Questions Answered