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Hey chaps, I have just been asked by a regular client to look at fitting them some dimplex mat type under tile heating, thing is they have as far as i can see been intended to be powered via an rcd fused spur, taken off of an existing ring main socket spur cable. Anybody know if this is the kind of feed size needed or if an Rcbo would be needed at the consumer unit to cover the cct if I was to feed the system from an existing socket on a ring circuit ?

I have in the brochure only info regards the max mat size rated at 780 watts which is 3.39 Amps approx so do I take it that this is the only load I need to supply for ?? as in possibly power from a spur feed off a lighting cct or water heater supply ? Other nightmare is as far as cutting in a fastafix box for the rcd spur and programmer is that the walls are still covered in laughing plaster ( lathe & plaster ) which is always a pig ! if anyone has any tips please forward them ! The final thing is that the floor is only old battered up floor boards and it mentions the need to lay 18mm ply or tile backer board to provide a sound surface to lay the matting onto which by the time tiles are laid will surely raise the ffl sufficiently to make closing the door etc impossible ! lol... cheers for any help guys and or girls, Matt. :D
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  • Thread Starter Thread Starter
  • #2
You'll need to rcd/rcbo the circuit or use a rcd fcu off the ringmain.
As for the lave & plaster get yourself a fein multimaster, it'll take all the hassel out of the first fixing into L&P.
Yes you'll need to lay a thermal baseboard.

Some sites for you
Underfloor Heating Cablemat Installation Guide by Discount Floor Heating
Electric Underfloor Heating Systems - Under Floor Heating Mats

(I installed the under carpet carbon film kit for a customer a few weeks ago, not bad to do but still have to use base board & thermal seperator under the carpet)


  • Thread Starter Thread Starter
  • #3
As regards fitting a box in a lath and plaster wall,i would mark the position and then drill a series of holes around the outline its easy then to cut out with a pad saw or jig saw ,then fill the hole with bonding plaster ,put loads in then push the box into position,the plaster will spread out and set very solid quite quickly best to put the wire in the box first first
have fun:)
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  • Thread Starter Thread Starter
  • #4
Lath and plaster is a pig. Not sure there is an easy way to do a neat job with a firm fixing. Is there a cupboard near where you are wanting to put the FCU? If so, cut a chunk out of the cupboard wall - fit a batten across the joists (providing the things aren't diagonal!) then put a neat hole in the front and screw a KO box to the batten and put plasterboard inside the cupboard.

Trouble with tiles on floorboards is that the floor really isn't that stable. I'm having to replace our bathroom because of a rotted floor thanks to a leaky shower, and it's in a newish loft extension. Shower leaked, water ran through between the ply and chipboard capilliary action and causing the floor to swell and crack. Having lino this time, and making a better job of it than the builders.

But you are right, the floor will be VERY much thicker, and the door will need a bit of planing down. Also, if they choose tiles that are uneven thicknesses such as some natural material tiles, then the floor will be even thicker to compensate for this - so thick that the floor heating pad is ineffectual!! Happened to a mate of mine who fitted natural slate floor.

London Luke

  • Thread Starter Thread Starter
  • #5
I do many underfloor installs.

INsulation is very very important. I also demand to lay 2 mats and 2 x probes. then if one fails i have another to hook up quickly. Ive seen mats fail within a few years etc due
to poor tiling etc .
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