Electric ufh not reaching desired temperature

[ash1212002]

Apologies in advance for the long post, hope someone can advise

We've had our floor tiled a couple of weeks ago. This week we put the underfloor heating on for the first time and gradually increased the temperature by 5 degrees per day

Today we set it to 27 degrees and it has taken 6 hours to get to 20 degrees! starting from cold at 10 degrees!

Currently it is showing as 20.5 degrees but have also noticed it goes to 21 but then drops rather than increasing to the 27 degrees I've set it to Is this normal?

We have 2 mats but one temperature sensor, we've also noticed where the mat is laid on the concrete side it is not as warm as the side where its a timber floor with concrete cement boards

Furthermore on the timber floor side some areas of the floor are considerably warmer than other areas of the same floor!? There are cold spots and lukewarm

Any ideas what could be wrong? Could it be the thermostat/sensor or something else?

 

[Madrab]

You've kind of explained it yourself. The flooring that the heat mat is in contact with is acting as a heat soak and that will create variations in temperature. The electric UFH should have been laid on an insulating thermal matting to minimise the amount of heat traveling down into the flooring and miximise the heat traveling upwards keeping the heat relatively consistent across the floor.

If the fitter hasn't done this properly then you will always have problems as each material will draw heat away at different rates

 

[ash1212002]

You've kind of explained it yourself. The flooring that the heat mat is in contact with is acting as a heat soak and that will create variations in temperature. The electric UFH should have been laid on an insulating thermal matting to minimise the amount of heat traveling down into the flooring and miximise the heat traveling upwards keeping the heat relatively consistent across the floor.

If the fitter hasn't done this properly then you will always have problems as each material will draw heat away at different rates

I think it could be due to lack of insulation not being laid on the concrete side, however on the timber floor side concrete cement boards were laid some areas are nice and warm on the timber side as per expectations however the rest of the timber floor with cement boards laid is luke warm!?

 

[ericmark]

I laid electric underfloor heating in my mothers wet room, first it was band jacks to remove concrete floor, then 9 inches of insulation, then plywood then heater and finally tiles, there was a pocket for the sensor although that did not work as sensor got jammed so when I came to renew I couldn't.

The idea is the maximum temperature is 27°C, in real terms that means surface of floor lucky to reach 25°C as sensor is under the floor, so even with insulation it was really a failure. Idea was to dry floor faster, and since wet room had to use type with earthed outer, we could not use raychem.

I am told RayChem is better as the heating cord alters properties to maintain temperature and does not require under floor sensor.

However to work has to be on 24/7 and clearly if insulation has not been fitted your heating the ground below the house.

As said the sensor failed on ours, and I found even with no sensor the floor would only just hit 30°C, no furniture in a wet room of course, so I took a chance and used it without a sensor, but even on 24/7 and no sensor it was still rather useless, without the towel rail the room would never get warm. In the summer when switched off we realised the floor was still warm to walk on, and next winter we rarely turned it on, and it became clear the advantage was not the under floor heating but fact insulation had been laid first, so yes after fitting the floor was warm, but not due to heating, just simply the insulation.

With that in mind clearly if no insulation then it would cost a fortune to run, and be useless anyway.

Measuring floor temperature I also found a problem, I used my beer controller, and a sponge, however clearly as using a sponge to stop air cooling the sensor, it would always read a little high, suppose one of those guns are best, but expensive, and does it matter, nothing you can do to get it warmer, so why bother measuring it?

 

[ash1212002]

I laid electric underfloor heating in my mothers wet room, first it was band jacks to remove concrete floor, then 9 inches of insulation, then plywood then heater and finally tiles, there was a pocket for the sensor although that did not work as sensor got jammed so when I came to renew I couldn't.

The idea is the maximum temperature is 27°C, in real terms that means surface of floor lucky to reach 25°C as sensor is under the floor, so even with insulation it was really a failure. Idea was to dry floor faster, and since wet room had to use type with earthed outer, we could not use raychem.

I am told RayChem is better as the heating cord alters properties to maintain temperature and does not require under floor sensor.

However to work has to be on 24/7 and clearly if insulation has not been fitted your heating the ground below the house.

As said the sensor failed on ours, and I found even with no sensor the floor would only just hit 30°C, no furniture in a wet room of course, so I took a chance and used it without a sensor, but even on 24/7 and no sensor it was still rather useless, without the towel rail the room would never get warm. In the summer when switched off we realised the floor was still warm to walk on, and next winter we rarely turned it on, and it became clear the advantage was not the under floor heating but fact insulation had been laid first, so yes after fitting the floor was warm, but not due to heating, just simply the insulation.

With that in mind clearly if no insulation then it would cost a fortune to run, and be useless anyway.

Measuring floor temperature I also found a problem, I used my beer controller, and a sponge, however clearly as using a sponge to stop air cooling the sensor, it would always read a little high, suppose one of those guns are best, but expensive, and does it matter, nothing you can do to get it warmer, so why bother measuring it?

We've spent just over a grand to get the underfloor heating installed which includes materials, concrete cement boards, primer, self leveller etc

2 separate 200 watt mats in one thermostat 6sqm and 10sqm

In in another room 11sqm we haven't switched this one on yet going into another thermostat

Really disappointed I wasn't expecting this, a great expense which we'll have to take the loss on.

Good job we've kept the radiators!

 

[muggles]

A 400w mat is never going to be enough for primary heating in a room that size. You need about 100w/square metre for that, so 1600w in your case. Sounds like whoever specified the UFH either didn't realise you wanted to use it for primary heating, or didn't know what they were doing

 

[stem]

A mat of that capacity is really designed just to keep the tiled floor warm so that it is not cold to walk on with bare feet. Not to heat the room, but as you say you also have radiators as your primary heat source that that's probably how it's been designed, and if so, it sounds right to me. Use the radiators for primary heat (costs about one third the cost of electric heating) and just use the electric UFH to keep your toes warm.

 

[Madrab]

2 separate 200 watt mats in one thermostat 6sqm and 10sqm

Is that 200w per sq M? Or total?
As @muggles mentions 200w in each mat in total will only warm the tile, hopefully it isn't. Ideally I would think you really need up to 200w per sqm for it to give you enough to control the heat in the room properly, Hopefully it's the latter.

Ouch, unfortunately that's a lot of cash for something that doesn't sound like it has been installed properly I'm afraid.

 

[ash1212002]

Is that 200w per sq M? Or total?
As @muggles mentions 200w in each mat in total will only warm the tile, hopefully it isn't. Ideally I would think you really need up to 200w per sqm for it to give you enough to control the heat in the room properly, Hopefully it's the latter.

Ouch, unfortunately that's a lot of cash for something that doesn't sound like it has been installed properly I'm afraid.

Its 2mm thin 200w per sqm cable mat

 

[Madrab]

Hmm, so what is the room stat showing, should be air temp, not floor temp. If so then it's not that it isn't heating the room rather the heating across the floor area is inconsistent?

I have 200w m2 in my en suite and it can achieve pretty close to the set stat temp, I've had the room up to 25Deg without issue. I laid 5mm of airtex foiled insulation with 15mm of foam, that's on top of a P5 floor with 5mm WBP ply and tiles on top. I have it set at 22deg and it sits around 20ishdeg, the heat in the floor is around 37/38deg.

If it's 200w per m2, then it is should be considered as the primary heat source installation, that means it should be able to sustain a suitable heat in the floor evenly enough to heat the room properly. If the room is getting to 21Deg then it is getting warm but you must be losing too much heat to the subfloor if you can't get it any higher.

I hate to say it but it really sounds like it wasn't installed properly. When was it installed? If it was recent then I'd have them back to fix it, that will be fun though if it was tiled because it can't be lifted now without destroying it.

 

[ash1212002]

Hmm, so what is the room stat showing, should be air temp, not floor temp. If so then it's not that it isn't heating the room rather the heating across the floor area is inconsistent?

I have 200w m2 in my en suite and it can achieve pretty close to the set stat temp, I've had the room up to 25Deg without issue. I laid 5mm of airtex foiled insulation with 15mm of foam, that's on top of a P5 floor with 5mm WBP ply and tiles on top. I have it set at 22deg and it sits around 20ishdeg, the heat in the floor is around 37/38deg.

If it's 200w per m2, then it is should be considered as the primary heat source installation, that means it should be able to sustain a suitable heat in the floor evenly enough to heat the room properly. If the room is getting to 21Deg then it is getting warm but you must be losing too much heat to the subfloor if you can't get it any higher.

I hate to say it but it really sounds like it wasn't installed properly. When was it installed? If it was recent then I'd have them back to fix it, that will be fun though if it was tiled because it can't be lifted now without destroying it.

On the timber floor side it was overlaid with 6mm cement boards, primed and the mat laid on top followed by the adhesive and tiles

The concrete side nothing, no insulation was laid as this would have increased the height of the floor. the floor was levelled using levelling compound which also encased the underfloor heating mat, followed by the adhesive and tiles.

We isolated the mat which is on the timber floor side, disconnected the sensor which only left the mat on the concrete floor side connected for approx 6 hours.

6 hours later the floor is barely warm! you can just about feel some warmth on the tiles

Should i leave it on longer? If so is there any risk of damage, overheating etc given that the floor sensor has been disconnected

The thermostat doesn't have an air sensor

 

[Madrab]

I am sorry to hear that as I'm afraid that just isn't enough insulation, actually next to none TBH. Sounds as if at least half the heat is getting sucked up by the cement boards and then heading into the floor below, from your description it doesn't sound like there is much, if any thermal barrier stopping the heat travelling south.

If you didn't have the available height in the floor to be able to put suitable thermal insulation into the floor then unfortunately electric UFH should not have been recommended as a heating solution for the room. Even with at least a reflective barrier a few mm thick it would have at least let the tiles get warm.

I am surprised that the thermostat doesn't have an air (internal) and floor sensor (remote) as part of the setup, it really should have.

 

[ash1212002]

I am sorry to hear that as I'm afraid that just isn't enough insulation, actually next to none TBH. Sounds as if at least half the heat is getting sucked up by the cement boards and then heading into the floor below, from your description it doesn't sound like there is much, if any thermal barrier stopping the heat travelling south.

If you didn't have the available height in the floor to be able to put suitable thermal insulation into the floor then unfortunately electric UFH should not have been recommended as a heating solution for the room. Even with at least a reflective barrier a few mm thick it would have at least let the tiles get warm.

I am surprised that the thermostat doesn't have an air (internal) and floor sensor (remote) as part of the setup, it really should have.

Your right, really disappointed and a great financial loss incurred!

It was never mentioned by the installer to install any form of insulation and i must say i did a lot of reading too and didn't come across anything to suggest to install a thermal barrier

The thermostat has a floor sensor which is 300mm in between the heating elements but definitely does not have an air sensor

I may leave leave the mat running for 24 hours on the concrete side without the floor sensor to see if their is any improvement in heat output on the tiles

But realistically running the mat for 24 hours before achieving realistic heat output will not be financially viable in the long run with electricity costs and consumption!

 

[Madrab]

If you don't use insulation then I would have at least expected the tiles themselves would at least get warm but again if the sub floor is of different types then the heat can be absorbed down the way quicker and at different rates, giving a patchy result.

If all you wanted was warm tiles then usually insulation isn't essential I wouldn't think but given the fact that electric heating is at least 3 times more expensive that say wet UFH then unless it's a tiny room I'd alway look to insulate as a matter of course.

Unfortunately all of this is moot though and really the only way to sort things out would be to lift it and start it again I'm afraid. Is your installer responsible, depends on what was the approach and agreement you had with them I guess.

 

[Nozzle]

Is this the ground floor?

The talk above about insulation is the key to it, and without insulation then the power from the UFH is mostly conducting into the floor rather than heating the air. Thin insulation rolls are available on the market but be sceptical about the performance claims made by really thin rolls. Insulation needs air trapped in pockets which prevents in moving. Thin insulation, by virtue of being thin, has very little space for enough cells to trap said air. The upshot is, thick insulation sheets are required, and in order to maintain the same finished floor level as the rest of the house means a huge amount of work.

Nozzle