1. Consider whether to opt for an electric or wet system
Electric underfloor heating systems are cheaper to install and wet systems are cheaper to run. If the consideration is to install UFH to a single room or small extension, then there may be an argument for an electric system. But running costs always win in the long run.
2. Know how much heat is needed
Any heating distribution system starts with knowing how much heat is needed. With a radiator system, it pretty much ends there as well. With UFH there are other issues that affect the design:
- The heat source (boiler or heat pump)
- The type and size of UFH pipe
- The type and location of manifolds
- The screed being used
- The floor covering all affect the design.
This is not something for an amateur and the key is finding a supplier that will produce an effective, clear and understandable design.
3. Choose the best type of UFH pipe for your project
A quick skim of the internet will reveal a bewildering choice of UFH pipes. Essentially these fall into two types: single layer plastic or multi-layer, which can be a mix of plastic and aluminium, or a mix of different plastics. The price varies with quality, with multi-layer being more expensive, but this is a job that only wants doing once and the price of the pipe is a relatively small part of the overall cost of the system. Multi-layer is unquestionably more efficient and more durable.
4. Invest in a good zone control system
A whole-house UFH system will have separate pipe runs to each room or zone. This provides the opportunity to control the temperature and timing of each zone to suit occupancy patterns. For example, the lounge will need to be warm through the evening while bedrooms need to be heated later in the day.
A good zone control system might cost £1,200, which will be more than repaid in energy saving and increased comfort.
5. Choose the right floor covering
Tiles, stone, slate and similar materials are the optimum coverings as they work in conjunction with the screed. Wood will tend to insulate and reduces efficiency but thinner profile (less than 20mm) engineered timber has little noticeable impact on heat output.
The Carpet Foundation carried out some research in conjunction with the Underfloor Heating Manufacturers Association, which showed that a carpet and underlay with a thermal resistance of less than 2.5 togs does not have a significant impact on UFH efficiency. (According to the Carpet Foundation, a typical 80 per cent wool to 20 per cent nylon carpet with a standard underlay will have a tog value of 1.0 to 2.2.)
Whatever floor covering is to be used, tell the UFH designer so that the pipe layout can be properly specified.
6. Know how different floor screeds affect performance
A typical floor screed will be 60mm to 75mm thick, and made up of sand and cement, often with glass fibre reinforcement. That thickness gives a two to three hour reaction time (to heat up and cool down) and means a different approach to timing the operation of the system. The alternative is a flow screed (or anhydrite screed) that can be just 40mm thick, giving a reaction time of less than one hour because it has better thermal conductivity than sand and cement.
7. Consider highlight heating
An up and coming option is to run the UFH 24/7 at a low level, maybe 15°C or 16°C, as a ‘maintenance’ level in rooms that are not always used and then to use highlight heating in those rooms being occupied. This can be a stove, fire, even radiators, particularly towel radiators, but could also be achieved by simply turning up the heat from the UFH in that zone.
This is a particularly useful strategy with heat pump systems, as they work more efficiently at lower temperatures. This approach also helps to avoid ‘short cycling’ — switching on and off in short cycles.
8. Know when a heat pump is best
The best heat source will vary with the screed being used. Ideally, a thin flow screed is used, in which case any heat source, boiler or heat pump will work well. If a thick sand and cement screed is being used, then there is an argument for the UFH to run continuously at a lower temperature (because of the long reaction time). In this case, a heat pump would be the preferred option.
9. Go ahead and retrofit
The worries around retrofitting and UFH have been with us for as long as we have had UFH — and the industry has been working on it for just as long. There are now viable solutions to virtually all situations, and if it ever was a problem it is no more.
In the case of a suspended timber floor in an older house, the effect of heat applied directly to old timbers needs to be considered. Changing the environment that the timbers are used to can cause twisting or warping. Again, speak to the designer and have those older timbers inspected.
10. Have an idea what you can expect to pay
- The cost of a typical, good quality wet UFH system will be between £20 and £30 per m2
- An electric system will be around £15 per m2, similar to a radiator system