Under floor heating questions for your edification and entertainment

[The Ghost]

So...Got a call late last night client who I have done work before asked advice re builder doing electrics. Advised re CPS membership he checked on ESR builder not on there. Asked builder was he CPS member. Builder said seems best we part company client left in the lurch with no kitchen just bare walls building work half done. Client down 8 G.
Agreed to do electrics on kitchen all good so far! UFH.. so he has UFH in bathroom adjacent to kitchen. And UFH under kitchen floor. Client suggested I put both heating mats on the one thermostat existing from the previous bathroom UFH. Bathroom is Klima/screwfix UFH and thermostat, new kitchen UFH is Heatmat. No evident thermostat cable coming up from floor. Clear so far? So for me its going to be a bit of a scramble sorting out three cables black and one cable white coming up from floor and sorting out thermostat(s) Any savants out there? This is a discontinued Tstat, and I have the file for it. I suppose the question is can you put an extra 12m² (Kitchen) onto existing 9m² (bathroom) existing thermostat. All answers will be treated in confidence of course.

 

[PEG]

Hi bud,if the two mats are separate areas,and there is a chance the thermostats are in,test out the mats and power up,then check the stats meter the temp rise.
This may be one of them jobs, where you don't give the customer too much say

 

[Gavin John Hyde]

I hate underfloor heating as its great if installed properly. But every so often you come across a utter bodge job and the flooring above the heat mats is crap.causing damage. Breakibg up etc...
I avoid it like the plague.
As for your question have you tried the manufacturer as they normally have a boffin or two sitting around who might answer the questions.

 

[Wilko]

Hi V - def not a savant on UFH so for what it's worth - with the mats in various watts /m2 and the stats switching capacity unknown, I agree with Peg - stick with existing arrangement and test - the mats may already be trashed as Gav reminds. Client had £ks vanished with last builder so might be best to keep the work in small chunks, in case the worst happens. Not very cheerful this morning, sorry.

 

[The Ghost]

tried the manufacturer

Thats the next stop thought I would assay things from the forum first because everywhere else is closed.

thermostats

Yeh thats the thing, there is only one thermostat for the bathroom. The builder did not see fit to install one in the kitchen underfloor (sigh) so only the one thermo. I did say I can't put the both mats on the one thermostat.

Not very cheerful this morning, sorry.

Sorry to hear that!
When on site yesterday met with live sockets off walls and hanging in the middle of the room, this is a family home with kids, really bad case of builder electrics. At least the client caught on when the builder said he will do the electrics and got in touch with me. They have no kitchen so about to put in place triage/emergency installation the UFH can go hang for now lets get them a cooker etc.

 

[Octopus]

Now is the time to redo it properly..... Not later when it's all fitted out and decorated...

 

[The Ghost]

fitted out and decorated

Yes I have come to that conclusion. It means pulling up some tiles to fit a sensor, which has not been installed. But, not much choice on that one as far as the tech are concerned there has to be a sensor underfloor, which makes sense to me.

 

[Octopus]

Good call.

If you don't do this now any issues down the line will be your problem.

 

[The Ghost]

will be your problem

Those dread words... just thought, can't pull up the tiles it will damage the heat mat...

 

[Wilko]

Bolting Builder has not only taken money, but he's made off with a floor temp sensor? Now that is taking it one step too far ... I have heard folks put in 2nd sensor as a spare, such is the pain of replacing them after the event. Aghhh

 

[PEG]

Where there is a will,there's a way... if the MI states an underfloor thermostat is a requisite,it needs one,or leaving it a worker is not possible.

The MI of most,require the thermostat to be placed in between the elements,and although the middle is usual,if the base/substrate is not thermally retentive,nearer the edge would suffice.

In fact,if the "thermal mass" is solely the tile/adhesive,then any position which places the thermostat half the measurement from a heating element,of the distance between runs of element,will read the temperature rise.

This may allow placement of the correct thermostat (if that can be determined) with judicious use of a diamond blade in a mini-grinder with depth-stop at tile thickness.

All of the above is pretty radical intervention,and would necessitate the approval of your customer,and possible failure accepted and paid for...but the alternative is a bus ride from foot warming

 

[The Ghost]

All of the above is pretty radical intervention

Good idea. Spoke with the tech. today (Klima) who said the room temperature aspect of their thermostat would be satisfactory without a floor sensor to my surprise. They suggested putting it close the the floor. Now that is what they said, but I am not convinced about that to be honest. I am the sort of person that could probably do a surgical intervention of that order, and await to see if the client can get any info from the builder as to what the hell he did exactly. It would seem he has cover the whole (4m x 3m) 12 sq m. with a mat, just really don't know at this stage so kitchen furniture will be going on top of the heat mat (not good) it is looking a bit grim for the client at the moment but I have not told them til I know better.

 

[Wilko]

Picking up on the tech advice, Peg's suggestion and builders mat placement ... if the mat is under the cupboards, perhaps butcher surgically insert it under there? Out of sight, air circulation will be less and even if it's not in exactly the right place at least it's still got one.

 

[sam400]

you can run 2 mats of of one thermostat/controller if the contacts are suitable rated, if not I have used a contactor in an adaptable box to run large areas off of one controller before.
Also on some controllers have an option to look at room temperature for control rather than floor temperature.

 

[Toneyz]

I think they will have to bite the bullet take up a tile and install correctly with sensor this is how it is supposed to be installed for the heating to work effectively and efficiently. I am sure that there was spare tiles left /still available better to do it right than in the future get calls regarding it not working correctly.