Max UFH temp for screed floor??

[jgtr]

Hello

Does anyone know the max input water temp for UFH in screed?? Currently I have it set to the recommended 45 degrees, if I go higher is there any risk of damaging the screed or is it just a case of wasting energy???

Had UFH fitted in my new build conservatory, pretty sure screed is too thick as takes an age to heat up. I'm playing with setting trying to find out what works best - wanted to try a higher temp to see if it makes any difference.

Thanks

Jay

 

[Aquaheat]

A bit more information about your set up would be helpful. What is the thickness of the screed, when was it laid, what was the underfloor laid onto, how long is it taking to reach temerature in the conservatory? Remember that UFH is not designed to be roasting hot but a comfortable background warmth and is not designed to be turned on when you want heat instantly rather it should be left on a continuous program and the room stat that is installed will control that particular zone as and when requied. 45 degrees will be plenty in a correctly laid and designed system. If you are having to increase past this then there are underlying issues that need addressing.

 

[jgtr]

100-120 mm screed, laid in January, has been heated properly so it doesn't crack etc,over 75mm celotex. The underlying issue is that the builders are idiots. Despite being clearly told to lay 80mm and having a datum line around the wall I came home to find they had laid the screed too thick. Heating came on at 05:00 this morning and 2 1/2 hours later has only gone up 2 degrees which is probably because the sun has come up. I'm using a UFH programable room stat and am currently experimenting with setback, as you say keeping the slab temp low over night and during day and boosting it mornings and evenings when it's coldest. I was just curious to see what effect increasing inlet water temp would have but didn't want to damage the screed.

 

[muggles]

Did they put edge insulation in around the screed (normally blue or white foam about 10mm thick)? If not, beware turning up the flow temp as the additional expansion of the screed will push your walls out

 

[jgtr]

Yep, used a roll of foam supplied with the kit

 

[Aquaheat]

Ok jgtr, well the system should have been designed to allow somewhere between 45 and 55w/hr of heat. This dictates pipe centres etc to get the right amount of pipework under the floor to put it simply. This however would be assuming a seed depth of 80mm, as you said you suspect 100 - 12mm has been laid effectively adding anywhere between 25 and 50% extra material to heat up. This is going to massively impact the response time of the heating, in theory it will get there eventually assuming the heat input exceeds the heat losses but I think you could be fighting a losing battle. Increasing the temperature through it isn't really recommended and could possibly damage the screed and floor covering (I'm assuming tiles). Out of interest does it ever reach temperature if left on constantly without using any night setbacks? Also after running for a good while what's the maximum floor temperature that you reach?

Jon

 

[jgtr]

I've got the floor temp (imbedded probe) set to 32 degrees, I haven't got a floor temp sensor but I doubt it gets above the recommended 27. Just on a hot day without heating I've had 38 degrees on the imbedded sensor! Problem may be at present its not cold enough to run during the night (currently at 18 degrees ambient) so I'm starting with a cold slab each morning?? It does eventually get warm but just takes time so maybe in winter I start it earlier or use the imbedded temp sensor instead of ambient toaintain heat in the slab but I can't switch between the 2 very easily, may be ok in very cold weather. Maybe I'll keep water temperature the same and try adjusting timings, only just started with the settings so room
for improvement. As a guide heating came on at 5:00 am and flor wasn't warm until 08:30

 

[Agile]

It sounds as if you are not fully in control of your heating. Could you have weather compensation which is affecting the UFH as well?

45 C is the normal maximum for flow temp into UFH. Also the flow rate should be enough to give a return of no more that 10 C between flow and return.

Certainly your cover is higher than recommended and this will take longer to heat up and cool down than even the usual 2 hours.

My recommendation is to have a setback temperature of say 25 C flow at all times when the heating is going to be needed.

Max floor temp is normally meant to be 30 C as more becomes uncomfortable to walk on with bare feet.

UFH is best designed by a heating engineer and not builders.

By careful control you should still be able to get good results.

Tony

 

[jgtr]

Thanks Tony, I think the weather definitely affects it at present, would be good to be able to use different sensors at different times of the day so at night I could keep the slab ticking over and during the day use ambient temperature. I think with the cold weather it will be easier to control, at present the weather changes so often it's hard to modulate the temp with the controls.....but hey it's a conservatory. Maybe an air blower for this time of year, the dyson ones are pretty good.

 

[Aquaheat]

Not at all jgtr, there will be a tupperware solution for this! I'm not the best to speak to about it but I'm sure that there will be a few along that could help. What existing controls do you have and what boiler is it running off?

 

[Agile]

Whatever the system there is a one off Tuppa solution available.

Its best done in software but that requires both software knowledge as well as a one off interface for each part of the system requiring control.

Few installed systems lend themselves very well to computer control.

Tony

 

[jgtr]

My boiler is a Viesmann 100-W system boiler, approx 2 years old, 26 kW IIRC (4 bed detached house). UFH control is a Heatmiser neostat-e programable roomstat. It was working ok yesterday, just takes a longer than normal to heat up, was lovely in the evening just a bit slow first thing.

What's a Tuppa?? I'm presuming bespoke heating control but can't find anything on Google??