Install your own Underfloor Heating

It's no wonder self-builders have taken to underfloor heating. It is an energy efficient way of heating a room that doesn't suffer from the hot and cold spots of traditional radiators and frees up all that new wall space. What's more, the convection currents created by a radiator tend to distribute dust around the room whereas underfloor systems provide a much more even, comfortable heat.

A dry electrical matting system is the one of easiest systems to install if you want to save money and tackle the fitting yourself, and ideal as a retrofit solution in a bathroom or conservatory laid beneath tiles.

Here we show how to install the Enermat 2 Magnum system distributed by Enerfoil. Its 3mm thick cable has a heating capacity of 125W/m2 and can be laid directly onto concrete floors in a screed of flexible tile adhesive. The product comes with a ten-year warranty and, for 9m2 worth, costs around £492 including sensors to control output.

1. Sweep the floor to remove any chippings or anything else that may puncture the cable sheathing. Remove any inward opening doors, kickboards and skirting board. The floor level will be raised by around 6mm plus the thickness of your tile. Unless you are a skilled tiler, its probably best to lay the matting and fit the tiles once the first screed is dry so plan the work in manageable sections.

2. Mix the tile adhesive according to the manufacturers instructions. It should be lump free and a smooth pourable consistency to fully coat the mat and wiring without leaving air pockets. Only make up enough mix that you can use in around 45 minutes

3 For timber floors, you can either fit a cement-based board (such as Aquapanel or Wedi) to the plywood or screed with a 3mm layer of flexible tile adhesive: see section on Timber Floors. Leave to fully dry before fixing the underfloor heating

4. Starting at the conductor cable end, plan out the position of the first layer of matting. Note: the matting is always laid with the wiring facing down. Start the matting as close to the position of the wall thermostat as possible

5. Cut the glass fibre matting to fit around the room. Generally, the matting can be laid in a zig-zag pattern across the floor. Do not lay the matting under kitchen units and don't overlap the wiring

6. The system is supplied with a separate sensor that is wired directly into the thermostat. This must be fitted inside electrical conduit and placed in the floor near to the thermostat position. Seal the tip of the conduit with silicone sealant to prevent tile adhesive setting around the sensor

7. To take an accurate reading, the tip of the sensor cable must be placed between 400 and 500mm from the nearest wall. The end of the matting conductor cable must also be enclosed in conduit. Before installing the underfloor heating, a resistance reading should be taken and noted down. This should be kept in a safe place and other readings taken during and after installation to make sure the cable hasnt been damaged before connecting to the thermostat

8. The sensor is buried in the existing floor surface so that the conduit is flush with the surface. For timber floors, form a shallow groove with a router and straight cutter, for concrete floors use a cold chisel and club hammer to form the channel

9. Work out the position of the rest of the matting. Remember to keep at least 50mm between the wiring loops and leave the same amount of space between the wires and any walls

10. Start to spread the flexible tile adhesive over the first area to be laid. Work to a width of around 550mm so that the matting is bedded across its full width. There are several ways of laying the tiles. They can be laid in sections as you lay the matting, or after the first screed over the matting has dried. If youre not an experienced tiler, its probably best to work in two stages and fit the matting before adding the tiles

11. Whichever method you choose, its important to make sure the wiring is fully bedded into the screed. A trowel or roller can be used to push them into the mix. Check that there are no air pockets left around the matting

12. Work across the room, laying the tiles in the normal way. Avoid cutting the tiles near the matting as the shards can damage the cable. Complete the tiling and grouting and follow the adhesive manufacturers instructions before turning on the heating. Before everyday use, most suggest the floor is gradually brought up to the working temperature over a few days, then left to cool

13. The thermostat that comes with the Enerfoil system has several modes and is fully adjustable for weekday and weekend variations. Mark around the back plate to fix to the wall.

14. The back of the thermostat is clearly marked for the sensor, conductor and mains wiring. However, always have the connections made by a qualified electrician. The power cable and sensor cable should be run in separate conduits to the thermostat and must be wired through a suitably rated MCB or RCCD. Allow a minimum of 14 days for the humidity to drop to normal levels before starting to commission the new heating.

All prices quoted are correct as of December 2003

Further Reading:

• Underfloor Heating or Radiators?
• Underfloor Heating - Your Questions Answered