Bad UFH Heating installation wet pipes under 120mm Screed

[Biggiemanbiggie]

I've had wet UFH for 12 years and it takes hours to heat up our rooms. My gas bills are extremely high especially now due to rising costs.


i'm not getting a minor renovation and my builder has discovered that the pipes are under 120mm of screed. ATM the concrete takes hours to heat up but then it does release heat for several hours.

It does have thick insulation boards under the pipe so if there's no downward heat loss i'm wondering if i'm losing heat or does the concrete just act like a storage heater.

Now i'm wondering if it's worth me doing retro fit on around 100m2 flooring at a cost of probably around 18k would it ever pay for it self or do I just live with the buried pipes

 

[DP]

UF heating should be run at required temperature and set back temperature. Lot more efficient than panel rads.
Takes a lot longer to reach temperature. But once there not much required to keep it there.
Are the UF heating areas zoned with thermostats?

 

[Biggiemanbiggie]

Thanks for response i've also noticed the UFH maintains the heat.
My flow rate at the moment is 55 and my bills are crazy.

Yes all the rooms are zoned. Wouldn't the 120mm concrete make it inefficient ?
am I better lowing the flow rate but keep the heating on 24/7.

At the moment am airing towards a retro fit on top so my bills are reduced long term

 

[Biggiemanbiggie]

This is my graph from my thermostat

 

[Biggiemanbiggie]

I guess what i'm trying to figure out is if my UFH has been botched
as I have 110mm PIR i'm guessing 120mm Screed is ok as it's a different kind of design

 

[oldbutnotdead]

UFH is always going to be low and slow. 55 sounds quite hot- do you have radiators upstairs as well? Is there a blending valve at the UFH manifold?
If you have 100sq m of UFH you probably have a largeish house. High ceilings? Lots of windows? Hello large heating bills.
As you said you've got a giant storage heater. The heat stored in the concrete is mostly coming into the house (thanks to the subfloor insulation) but if your lifestyle is house empty for half the day you aren't there to see the benefit.
If your lifestyle is house empty half the day, think about putting some radiators in rather than ripping up what sounds like a decent quality ufh system. The radiators will heat the place quickly (for the morning flap), use the UFH for evenings/weekends if you want to and/or as a comfort thing (warm floors are lovely). If/when life changes and the house is occupied 24/7 then run with the UFH again.

 

[Biggiemanbiggie]

UFH is always going to be low and slow. 55 sounds quite hot- do you have radiators upstairs as well? Is there a blending valve at the UFH manifold?
If you have 100sq m of UFH you probably have a largeish house. High ceilings? Lots of windows? Hello large heating bills.
As you said you've got a giant storage heater. The heat stored in the concrete is mostly coming into the house (thanks to the subfloor insulation) but if your lifestyle is house empty for half the day you aren't there to see the benefit.
If your lifestyle is house empty half the day, think about putting some radiators in rather than ripping up what sounds like a decent quality ufh system. The radiators will heat the place quickly (for the morning flap), use the UFH for evenings/weekends if you want to and/or as a comfort thing (warm floors are lovely). If/when life changes and the house is occupied 24/7 then run with the UFH again.

Thanks yes I have upstairs rads so yeah I run at 55 to heat upstairs else it's cold. But during this renovation these are also changing to low profile UFH.

I guess then I can bring the flow rate down and run for longer instead of over shooting, yeah we spent alot of time at home especially with working from home. From what your saying it's not a botched install even with 120mm screed I guess this isn't a low profile system.

My heating bill was predicted to be £650 ish just for gas for a 2700 sqm house i'm hoping if I run lower at 40 deg and run for longer (keeping the concrete heat topped up) and not over shooting i'm hoping to bring my bill down.

 

[oldbutnotdead]

If you've got rads and ufh there really should be a blending valve (usually at the UFH manifold) to drop the UFH temperature - think 40° odd is recommended. And with 2700 sq m to heat you're going to have significant bills whatever you do... (even with 2 floors that's a footprint of 25m x 50m ish. Standard UK house nearer 8m x 10m.... you sure you don't have a stray decimal point somewhere?)

 

[robinbanks]

No way your UFH will be heating your concrete to 55 degrees unless you have some seriously thick insulative floor coverings (thick underlay and deep pile carpet); it'd make the house insufferable otherwise.

I'd assume there will be a TMV somewhere making the feed to the floor a more sensible figure. UFH has a long response time in screed and it's something you're supposed to work with (insulate and draft proof the house well, then run the UFH continuously at a low level) rather than against (have a poorly insulated house and blast the UFH up to a high temperature twice a day). 120mm of screed is going to take many hours to heat; it's got a huge capacity for heat storage

If there are insulation improvements that could be made in the house, I'd say spend the 18k on that instead.

Also, regards some of your figures:

* 120mm is incredibly thick; around 3 times what I'd have expected for an insulation supported screed; are you sure it's right?

* 2700sqm is enormous, getting on for 30 times the size of a typical new 3 bed house. Are you sure you didn't mean 2700 sq ft?

 

[Biggiemanbiggie]

If you've got rads and ufh there really should be a blending valve (usually at the UFH manifold) to drop the UFH temperature - think 40° odd is recommended. And with 2700 sq m to heat you're going to have significant bills whatever you do... (even with 2 floors that's a footprint of 25m x 50m ish. Standard UK house nearer 8m x 10m.... you sure you don't have a stray decimal point somewhere?)

Thanks again

No way your UFH will be heating your concrete to 55 degrees unless you have some seriously thick insulative floor coverings (thick underlay and deep pile carpet); it'd make the house insufferable otherwise.

I'd assume there will be a TMV somewhere making the feed to the floor a more sensible figure. UFH has a long response time in screed and it's something you're supposed to work with (insulate and draft proof the house well, then run the UFH continuously at a low level) rather than against (have a poorly insulated house and blast the UFH up to a high temperature twice a day). 120mm of screed is going to take many hours to heat; it's got a huge capacity for heat storage

If there are insulation improvements that could be made in the house, I'd say spend the 18k on that instead.

Also, regards some of your figures:

* 120mm is incredibly thick; around 3 times what I'd have expected for an insulation supported screed; are you sure it's right?

* 2700sqm is enormous, getting on for 30 times the size of a typical new 3 bed house. Are you sure you didn't mean 2700 sq ft?

The TMV is around 45 at the moment I don’t run constantly at the moment I heat for 4-5 hours overshoot and leave it off.

Sorry I meant the house is 2700 sqft yes the screed is showing around 120mm at the moment which is why I’m contemplating refitting. But as you say 18k is a lot of money may be I should try and live with it and keep it on 24/7 but at much lower flow rate.

 

[robinbanks]

If you redid the screed thinner it would heat up quicker, but overall the house would still lose heat at the same rate as before so you still have the same problem; you're suffering a loss and paying to throw consumption at overcoming it

If instead you take that 18k and use it to insulate and draft proof the house you reduce the loss you're suffering which means you no longer have to pay to overcome it

 

[Biggiemanbiggie]

Actually I’ve just remeasured
And the builder is including the screed from the bottom of the pipe. So it’s actually

100mm pir boards
And 90mm screed and this is actually the edge so may well be lower in other places

Doesn’t appear to be worth ripping out just for that as I know ideal is 60mm to 70mm

 

[Mr Chibs]

This year I decided to run my heating 24/7. I have 30m² wet UFH and radiators everywhere else.

I've been able to get the temp to around 18ºc with a boiler flow temp of 45ºc.
So far gas usage has been lower than previous years, although I was running at 19ºc previously.
If the UFH section the temp never goes lower than about 17ºc if it's -ºc outside.

I'm favouring running the boiler lower and continuously, which I shall continue until it's warm enough for it not to come on.

My PIR is also 100mm. I have liquid screed around 65/70mm and tiled floor.

 

[robinbanks]

Doesn’t appear to be worth ripping out just for that as I know ideal is 60mm to 70mm

It wouldn't be worth ripping out in any case; you're trying to solve a problem caused by an incorrect usage pattern. Better to insulate the house and run the UFH constantly; it doesn't matter what thickness the screed is then, and you're prepared now for changing usage patterns of the house (eg when you're older and home more)