Electric underfloor heating probe location

[Marnhullman]

I am laying some insulation boards then a heat mat followed by a latex screed then Amtico flooring. The Heatmiser room stat has a heat probe which it is recommended should be located as close the centre of the room as possible but I understand the probe should not cross the heat map wires so how do I get the probe to the centre?! Should I channel the insulation board below the mat and lay the probe wire in that or should it be laid in the latex screed on top?

One other thing: the probe is supplied with only 3m of cable but that can be extended using Beldon 8451 twisted twin cable. Can that be joined satisfactorily under the floor?

 

[ericmark]

The probe can fail, so it is put in a pocket, i.e. a length of pipe, the floor surface should not exceed 27°C the whole idea of the probe is to switch off the system should the floor get too hot, so not right on the edge, but neither does it need to be in the centre.

If you use a chemical heating system it is self regulating and does not need the probe, Raychem for example, and it will also reduce output when items placed on the floor, so easy chairs don't need to be the type on legs so there is free air passage for whole of floor.

I would test the pocket, in my mother house it got stuck, but to be frank the floor never got that warm so was not really required, it was in her wet room lucky it also had a towel rail or it would have been rather cold. I did not use Raychem as in a wet room it needs a bonded earth mesh where it was built into the resistive wire type, it was a failure, however the 9 inches or so of insulation put below the heated floor resulted in the floor being warmer than the other quarry tiled floors even with the heating off.

 

[Marnhullman]

Helpful advice re. no need for the probe to be in the centre of the room.

 

[Murdochcat]

The sensor needs to be centrally between 2 of the heating cables

 

[ericmark]

When as said the sensor got stuck in the pocket, I ran it without the sensor, I was to start with worried it may over heat, however in the winter it never seemed to exceed 30°C even without the sensor, although really a failure, as LABC insisted in an extractor fan, so replacement air was from hall, typical around 18°C which is too cold for a wet room, and the floor simply could not heat the air fast enough, in fact even with fan off, room still too cool, lucky there was a large towel rail as without it the room would have been far too cool.

We thought since the wet room was only used for showering in may be every other day, the cost of UFH for when having a shower was acceptable, however the problem was heat up time. I would set an alarm for 5 am and come down stairs to switch it on ready for my mother to have a shower at 10 am. This was as well as central heating kicking in at 7 am.

My sister had sung the praises of UFH that her friend had, but after using it, when we went to buy a new house, any house with UFH was not even considered, it may not drop the selling price of the house, but does make them harder to sell. The owners of houses with UFH thought it was a selling point, we never actually said it was the reason for rejecting the house, our worry I will admit was no way to find if insulation fitted or not, so take pictures of the insulation to show buyers when you sell the house, most were DIY fitted so no records.