Underfloor heating only luke warm

[blackbirdxx]

Hi,
Just had a Heatmat underfloor heating system installed by the builder as part of a bathroom refurb using porceline floor tiles. System is 160w, laid on timber floor on correct insulated boards.
Although the electrics appear to work, ie the thermostat lights up etc, the floor only gets very luke warm, even after 8rs on manual at 30 degrees C - hardly what I was expecting!
Builder keeps saying there is no problem and UFH is only secondary heat and shouldn't be hot. If that is the case, I would have invested in a pair of slippers rather than having UFH installed as at the moment its pathetic.
I have asked the builder to check the system and he keeps coming back saying that the electrician has checked it and its working fine.
What should my next course of action be, is the builder fobbing me off?
Should I request the builder get a representative of Heatmat to inspect it?
Should I be asking what resistance tests or sensor tests the electrician is getting. Not sure if he's even taken these at all?
Also, what kind of guarantee should the builder be providing?
Grateful for any help guys.....

 

[Nozzle]

How large is the area your 160W heat mat is installed in.
But I'm inclined to say the builder is right, you're expecting too much for 160Watt, it'll only take the chill off, it won't heat an entire room
Where is the temperature being measured from, floor or air?

Nozzle

 

[OvertonPlumber]

My 100watt devimat sitting under granite tiles gets so hot i can barely walk on it.
I even used it to bring on tomato seedlings!!
A builder should not of laid the heatmat only a tiler/ electrician. Normally the tiler puts it down and then the electrician terminates it and runs the insulation test before tiling to ensure its not damaged.
How is the controller setup floorprobe/ air sensor ?

 

[ericmark]

Although the electrics appear to work, ie the thermostat lights up etc, the floor only gets very luke warm, even after 8rs on manual at 30 degrees C - hardly what I was expecting!

That's 3°C too hot, 27°C is the maximum permitted. There are two completely different types of underfloor heating, RayChem uses a special chemical in the cable which increases resistance as it gets warm so it is unlikely to over heat even if some thing placed on the floor, clearly since the resistance changes pointless measuring it.

The cheaper systems have a pocket with a sensor in it within the floor to limit floor temperature, OK for likes of a wet room where nothing is placed on the floor, not really a good idea in rooms where items maybe dumped on the floor.

So builder seems to be right, with wet systems the water temperature is some times allowed to reach 32°C as it can't by its nature have hot spots, but it is laid on timber so 27°C is the limit.

 

[blackbirdxx]

Thanks for the responses guys, some of your Q's I'll have to investigate and get back. The overall bathroom area is appx 2mx3m with the mat probably covering 60% of this area. It was laid by a tiler and connected by an electrician. I do have GCH so this UFH will only be secondary heat but how warm should the tiles be getting and how long should it take to get warm? At the moment I feel the UFH to be a bit of a waste of money. That said, I haven't moved back to the house yet to give it a real trial.

 

[winston1]

At the moment I feel the UFH to be a bit of a waste of money.

We used to have a member on here called BAS who always said UFH was a waste of money and furry slippers were better. Seems he was right.

 

[333rocky333]

That's 3°C too hot, 27°C is the maximum permitted.

So builder seems to be right, with wet systems the water temperature is some times allowed to reach 32°C as it can't by its nature have hot spots, but it is laid on timber so 27°C is the limit.

Why does it say in the section 753 of 18th electrical regs 753.423 no more than 35 degrees

 

[SFK]

Is the 160W for the whole room or per square meter of your floor?

I ask as 160w for a whole room is less than the heat produced in your room if it was lit by 3 X 60W (old style) incadesent light bulbs.

And Note that a plug in oil or fan heater is typically 2000W.

160w of heat in a floor will make room feel slightly more pleasant on a cold morning, but it will not heat it.

Sfk

 

[big-all]

would suggest 160w would warm an area about 1.5m cubed if well insulated after perhaps 5 or 6 hours
if you have a well insulated bathroom off perhaps 2.5x3x4m[9ft hx10ftx14ft perhaps 1-1.5 kw after 5-6 hours
as said under floor is background unless super insulated

 

[Nozzle]

Underfloor CAN be used for whole house, it is in my ground floor. But that's wet and has available 23kW of boiler at the back end if so required. Heat loss calcs will indicate how much power you need to keep that room warm. The details you provide indicate 44.4W/sq m. Not enough. Who specced this?

Nozzle

 

[ericmark]

Why does it say in the section 753 of 18th electrical regs 753.423 no more than 35 degrees

Not a clue, however if you google "underfloor heating temperature" you will find many sites giving the temperature. Including this telegraph report it seems it depends on the floor and tiles can go to 30°C.

I fitted it in a wet room, and the under floor sensor failed and got stuck in the pocket, so I had no limit to floor temperature, but it did not even if left on 24/7 get very hot, you could walk on the floor where outside on the beach some times hard to walk on the sand after the sun has warmed it. Idea was to dry the floor after a shower, however it was a failure, we had used sculptured tiles to get more grip, which held the water a little, and unless water swept off the tiles leaving them nearly dry it would take over an hour to dry, even after mobbing down, still took ½ hour to rewarm up and dry.

The hypocaust system died out,

I don't think it has ever worked, it was a good idea, but that was all it was, an idea, my son has fitted it in his own house, but not so much to warm the floor, but to sink the heat from the side boiler on the Aga, the huge amount of stone which is heated with the hypocaust or modern day underfloor heating means it retains the heat long after the heating has been switched off.

So we found switch it on at 7 am for my mother to have a shower, and off again a 10 am after floor was dry, and the floor felt warm all day, how much that was due to the insulation under the floor and how much due to heating is however a big question, as even after mothers death when we stopped using it, walk from kitchen to wet room and the wet room floor felt a lot warmer, it was on 9" of polystyrene block, then ply wood then heating element then tiles, the wet room floor was dug up to lay drains and all space above drains was insulation.

It seems you are allowed 55°C if the sensor fails, over that it can damage the floor, however when working correct then.

• Wet rooms not exceeding 33˚C and the perimeter zone of up to 1 metre 35˚C;

• Vinyl and Linoleum flooring not exceeding a temperature of 27˚C;

• High Duty Plastic sheeting flooring not exceeding 29˚C;

However in the main those higher temperatures are for water systems where by the nature of the system if the water is not over 55°C then there can't be any hot spots, our blood is 37˚C and we really don't want the floor that hot.

 

[blackbirdxx]

Thanks for the ongoing info...
Just to be clear, the mat used is 160w/m2 which is supposedly a good power to have in a bathroom as some mats are only 100w/m2.
Plan to go to the house again tomorrow to give the system another test. I wasn't expecting this system to heat the room just to make the tiles nice and warm in the morning after a shower - a bit disappointed!!

 

[Nozzle]

Comparing it to Roman UFH is folly! Smoke filled room. No control. CO and soot seeping through, HUGE thermal mass, difficulty loading fuel. How is that comparible with a modern Wet or dry UFH system? It's not! Modern Italians know that UFH is not only the past but also the future

Nozzle

 

[stem]

As has already been said it is 160w per metre square. So, assuming that is fitted to the entire tiled floor area (ie not under the bath / shower) which lets say for the sake of argument, for a typical bathroom floor is 2.5m x 1.5m that equates to 3.75m2 so 160 watts x 3.75 gives a total heat output of 600 watts when operating at full output (ie not being regulated down by a thermostat)

To put that into perspective a typical radiator for a bathroom of similar size would be about 1,500 btu's to 3,000 btu's (about 450 to 900 watts) depending upon how well insulated the room is. So based on that, unless your bathroom is badly insulated or drafty, it does appear that you should have a fighting chance of heating the bathroom adequately.

To prevent the floor getting too warm there will be a method of limiting the floor surface temperature. (not to be confused with the room temperature) With some heating this is adjustable within the room thermostat menu settings, with others it is fixed and you can't change it. However, your description of a lukewarm surface temperature is exactly what I would expect. Even though the surface is lukewarm it should be sufficient to heat the bathroom because the heat emitting surface has a much larger area than a radiator.

If the heating generated a higher floor surface temperature, then the bathroom would get warm quickly and the thermostat would switch it off, then the floor would go cold, the idea of UFH is to maintain a constant comfortable temperature to walk on any time. (to avoid the need for the aforesaid slippers) Therefore the best design would be to keep the floor surface at a constant comfy low temperature, and not fluctuating between hot & cold. Ideally you should be able to walk on the floor barefoot and not be conscious of it being either hot or cold.

So, if you are finding that the bathroom air temperature is warm enough, and the floor temperature is low, steady and constant, then it would appear that you have the ideal system. However, if it doesn't heat the room properly, or feels hot or cold to walk on, then something is amiss.

When you mention 30 degrees, is this in relation to the room temperature, or the floor temperature? If it's the room thermostat that's very high I wouldn't expect the room temperature ever to get up to 30 degrees, 20 to 22 degrees would be more usual for a bathroom. [The fact that a thermostat goes up to 30 degrees doesn't mean anything, the speedometer in my VW golf goes up to 160 MPH, but I know it would never reach it!]

Most UK heating is designed to the following criteria:

"Heating systems should be capable of heating to and maintaining a temperature of 21˚c when the external temperature is below freezing point"

 

[blackbirdxx]

Checked the system again and the thermostat runs off the floor temperature. How long would you expect the floor to heat up to the max 30 degrees?? I put the floor on manual mode with the thermo set to 30 degrees and the floor temp never went above 14 degrees.