09 Apr How to specify underfloor heating.
1. Make sure at the outset that UFH is compatible with the customer’s plans for the finished floor cover
Sounds obvious – but people do forget this basic precaution. UFH systems should be laid on flat concrete, ply board or insulation board surfaces and topped with a suitable floor leveller before the final floor covering -tiles, vinyl or solid wood. In particular great care should exercised when selecting wood laminates. Conformation of their suitability to be used in conjunction with underfloor heating is a must. Telling the customer this after you’ve installed the cable is not to be recommended!
2. Cables or mats?
As a rule of thumb, drums of cable are fine for smaller areas, especially where there are awkward obstructions, nooks and crannies to deal with – an en-suite shower room, for instance. For larger areas, mats which are simply unrolled and then fixed at intervals can save hours of installer time and make it much easier to achieve a regular spacing and an even heat output.
The Thermolay range offers a choice of rigid and flexible mats. The rigid mats, supplied in a roll and with pre-attached self-adhesive strips, are simply rolled out across a large unobstructed floor space. The Flexi-mats are secured with fixing lugs because the cable is attached to a stretchable mesh, which makes it easier to cope with obstructions such as washbasin pedestals or the unusual shapes of many conservatories.
3. Choose the right output?
With a choice of 160W/m2 and 200W/m2 Thermolay UFH systems will heat rooms of any size quickly and maintain the temperatures throughout the year. The choice of cable rating (W/m2) can depend on the rooms heat loss. For example in winter a typical conservatory will have a higher heat loss than a typical bathroom. The higher the wattage the quicker the response time in getting too and maintaining the set temperature on the thermostat.
Don’t mix and match cables or mats of different outputs in a given area, multiple mats will be controlled by a single thermostat (which must be controlled to the floor temperature in one place, not the room temperature).
Always allow 50-100 mm around the edge of the installation free of UFH and leave 30mm between mat runs. Then use the figures in the instructions to cover the area, using 120W/m2 output for wood and 160 to 200 W/m2 for concrete. For loads over 16A (3.67 kW) a mains coiled contactor controlled by the thermostat controller will be necessary to control the load.
4. Consider the need for complementary heating
Consider all the angles – UFH on its own (single source heating), in most cases, will not always be sufficient unless the scheme is designed to meet current building regulations (particularly with lower W/m2 systems). Heated towel rails maybe fitted or a radiator may be called for, so do the sums before telling the customers they can do away with radiators in a large kitchen, for instance.
5. Choose the best controller
There is a choice of thermostats on the market so do match your choice with the proposed use of the room being heated and the people who will be using it. Timeguard offers one of the widest choices of UFH controllers in the market. If sophisticated control with different timing patterns for different days of the week is called for, choose a top of the range controller like the RAM818top. Some people may like the easy to read large screen of a controller, like our new TPT88. Others may prefer simple on/off control.
Remember that you MUST install an RCD device – either an RCD fuse spur from Timeguard between the mains supply and the UFH controller or at the distribution board. With a Thermolay system the Timeguard guarantee is void if there is no RCD installed! It’s also good practice. Be sure to choose a system with a single ended 2-core cable, which connects, to the programmer, simplifying the installation. Connections are kept to a minimum.
Controllers must be supplied complete with an underfloor temperature probe to relay the floor temperatures back. Make sure this is up to the job – encapsulation in tough but flexible resin is best. You don’t want the hassle getting up the floor to replace it if it fails.
Take great care when laying the cable or mat. Check the floor surface is swept and free of potential damaging effects like a nail head sticking up. Check the impedance of the cable when you remove it from its packaging, check it at intervals when laying the cable and check it again when you have finished. If the cable is damaged at this point it can be repaired or replaced. But after the floor covering is on it’s much more difficult to replace. When cutting the mat fabric use scissors, not a knife. While working ensure soft soled shoes are worn and metal tools are either not used or kept well away from the cable.
6. Wait for the big switch on
It is tempting and everyone wants to feel the warmth between their toes but you really must impress upon customers the need to wait at least 10 days before switching on the power to allow the screed and any floor tile cement and grout to dry out properly.
The best policy is not to connect the controller and come back at the end of the drying out period for a ceremonial switch on. So much better than coming back to lift the cracked floor tiles!