Spur for electric underfloor heating

[Mike Atkinson]

I’m planning on installing some electric underfloor heating under engineered wood.

I’m looking at a Warmup foil heater system. It’s for a small room (approx. 2.5 x 2.5m) already with a radiator, so the underfloor heating is additional to ensure the floor is not too cold. Warmup’s literature shows that a 5m^2 pad is rated at 700W, drawing some 3A.

I intend to spur off the ring main at a power socket, connecting the thermostat via a RCD protected FCU (Warmup used to have one, now maybe discontinued?). Is there any reason why this instead would need to be on a separate circuit run from the consumer unit?

I plan to site the FCU close to the existing power socket just above the floor, with power running chased into the wall up to thermostat at “light switch level”. Warmup advise cables are in conduit and that cable for the temperature probe is in a separate conduit. Is this separate conduit necessary?

Although I’d argue I’m competent I’m certainly not qualified, and I believe such work is notifiable. What elements of this work needs to be left to a qualified electrician? All connections? Do I leave filling in until after sign-off? Is it recommended to find an electrician before work begins and then again when ready (I’m conscious this is a small job for an electrician who may not be willing to travel for little gain)?

Any pointers gratefully received! Many thanks in advance,

Mike

 

[flameport]

Underfloor heating is notifiable in Wales, but not in England. Part P doesn't apply in Scotland or NI but other requirements do.

If it is notifiable then the options are either notify building control yourself before starting, or have an electrician registered with one of the schemes do all of the installation and the notification.
There is no option for you to do some of it and get someone else to 'connect it up' or 'sign it off' or whatever else people incorrectly imagine can be done.

RCD FCUs are no longer listed in BS7671 for tedious reasons covered extensively elsewhere. However the socket circuit should already have RCD protection.
A 700W heater does not require a separate circuit.

The probe must be in a separate conduit so that it can be removed and replaced in the future, as they can and do fail.

 

[ericmark]

The pocket (separate conduit) for the floor temperature sensor is designed so that the sensor can be renewed without lifting the floor, I made an error, bend too sharp, and I could not get the sensor out to renew it.

All new cables buried less than 50 mm in a wall need RCD protection, including the cable from the socket to the RCD FCU, also the RCD used in the FCU is not normally compliant with list of BS numbers which the regulations say are required, it would depend how pedantic the inspector is, but really you need to have the whole of the ring final RCD protected.

There are two types of electric underfloor heating, resistance wire and chemical, the latter is self regulating, Raychem for example, but when I wanted to fit it, the chemical type did not have an earthed braid around the element so needed a earth mat where I was using it. It was a wet room, idea was to dry floor, it was a failure.

We I laid the UFH job one was lift the existing floor and fit insulation, to stop heat going down, around 9" of polystyrene under the plywood then the heating mat, then tiles, found even with UFH off floor was a lot warmer, no real need for the heated floor.

As to registering the work, needs setting up before you start, I had problems with the LABC they wanted to use an electrician on their list to do an EICR (electrical installation condition report) before they would issue the completion certificate. The cost of using an electrician on their list was more than the whole job. Could not use an electrician of my choosing, even if scheme member, had to be from their list. Remember I live in Wales so third party inspection not an option. In the end they did accept my signature on the installation certificate, I do have the qualifications and test equipment, although not a scheme member.

Although I’d argue I’m competent I’m certainly not qualified

The level of knowledge is classed as ordinary, instructed, skilled, then it was competent, although that class now dropped, so competent is over skilled, some one competent looks after the safety of others as well as themselves. The competent persons scheme is not the same as being competent.

The laying of the cables and the inspection and testing took well over a day, but was not done within one day, it was in three sections, this is the problem, getting tradesmen to work together, the first mat laid was wrecked by the guy tiling who tried to hide the damage with insulation tape. Could not repair, it needed a whole new mat laying.

The thermostat was also a problem, it takes a long time for heat from the mat to reach a thermostat, and when it turns off, heat is still coming from the floor, so you get a massive hysteresis.

There is a reason why the Hypocaust went out of fashion.

Most of it being the work involved to install it. Learn from history.