Retro UFH

[psirus]

Hi All

 

I am considering retro fitting UFH in my 1970s house.   I am really wanting to do this because the radiators just don't do enough in the open plan dining/living room area. 

 

Cavity wall insulation was added about 20 years ago by the previous owners and I have since added as much PIR to the pitched roof areas as I could fit.   Adding more radiators wont help much as all the heat will just go straight up away from where is needed.

 

The dining room ceiling starts at 3m heigh and finishes 5m, any heat from the radiator in the living room just spills out into the high dining room ceiling.  The pitched dining room ceiling has 50mm celeotex between the rafters.

 

My current plan would be to remove the screed which is roughly 6cm thick, lay 16mm pipes, liquid screed up to 30mm above the pipes.  That would mean only a 16mm increase in height across the downstairs floor which is ideal because only the dining room has a high ceiling the other rooms are all standard height. 

 

Please see attached photos to get an idea of the open plan space and the screed depth from a small test hole.  The rest of the downstairs is heated just fine by radiators but since the floor heigh will increase I would want to add UFH everywhere.

 

So my questions are should I do this?

Will it make a worthwhile difference or would I lose to much heat into the floor?

Should I put this project on hold and maybe one day dig out the entire floor and add extra insulation?  I cannot see this open ever happening as it would cost a whole lot more that just removing the screed but maybe I can be convinced.

 

Any other comments, concerns or advice would also be welcome.

 

Many thanks

 

[Declan52]

You need to first reduce the heat loss from the room before you think about ufh. 50mm is not a lot of insulation in a roof. Can you overboard the ceiling with insulated plasterboard to at least another 100mm more if the budget allows. You will lose the exposed beams but your house will be much warmer. 

Unless you sort the heat loss out then ufh will never heat that space. The heat will still go up and out no matter what the source is. 

Plus to go down the ufh route it will need 100mm min of insulation under the floor or all you heat will go down and there won't be much to heat the room.

[wozza]

Forgetting all of the insulation issues with your plan.

 

30cm screed above your pipes is not very thick, and if I remember correctly, there are not many products if any that can be used that thin on top of the UFH pipes.

 

Also is it me or are your maths a bit off, you say that you will remove 6cm of screed, lay a 16mm pipe with 30mm screed on top - meaning the floor level will be 16mm higher?  Minus 60 (after screed removed) + 16mm pipe + 30mm screed = Minus 14mm

 

Our extension vaulted ceiling has 100mm pir between the rafters and 75mm under. The floor has 120mm pir, with Cemfloor screed over the UFH pipes at around 55mm thick, the temperature stays very stable for a long time.

I spent a lot of time measuring the temperatures in our extension (3 UFH loops) to find the best place for the thermostat, and as @Declan52 has said, the heat will go up (its physics) and the vaulted areas will be warmer the higher up you go.

 

Edited July 28, 2020 by wozza

[psirus]

3 hours ago, Declan52 said:

You need to first reduce the heat loss from the room before you think about ufh. 50mm is not a lot of insulation in a roof. Can you overboard the ceiling with insulated plasterboard to at least another 100mm more if the budget allows. You will lose the exposed beams but your house will be much warmer. 

Unless you sort the heat loss out then ufh will never heat that space. The heat will still go up and out no matter what the source is. 

Plus to go down the ufh route it will need 100mm min of insulation under the floor or all you heat will go down and there won't be much to heat the room.

 

50mm is a lot more than what was there let me tell you!  But I take your point that really could do with more however we really didn't want to lose any of the exposed beams.  Even with 150mm of PIR in the ceiling I cannot see it making much different since the massive void with still take all the heat away from where it's needed at ground level when using radiators.  My thinking was that URH would keep the bottom half of the room warm the and top much cooler.

 

2 hours ago, wozza said:

30cm screed above your pipes is not very thick, and if I remember correctly, there are not many products if any that can be used that thin on top of the UFH pipes.

 

The Tarmac liquid screed that the screed guy quoted for is suitable to be used with only 40mm depth but it has to be at least 30mm above the pipes as well.  So technically I would have 46mm of screen as a thermal store.

 

2 hours ago, wozza said:

Also is it me or are your maths a bit off, you say that you will remove 6cm of screed, lay a 16mm pipe with 30mm screed on top - meaning the floor level will be 16mm higher?  Minus 60 (after screed removed) + 16mm pipe + 30mm screed = Minus 14mm

 

Yes you are correct I forgot to mention the 30mm celotex I wanted to put under the pipes.  I cannot seem to edit the original post to fix that.

 

Edited July 28, 2020 by psirus

[JFDIY]

Cemfloor quote that you can go as thin as 25mm over heating pipes if that helps.

 

See also webber 4310 as a member on here said you could do 30mm including pipes

 

https://forum.buildhub.org.uk/topic/13427-col57-introduction/

 

Edited July 28, 2020 by JFDIY
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[Declan52]

The heat will still rise, physics not much you can do about that, but with the extra insulation it won't be escaping. You will then end up with not needing as much heat. 

You will find that with ufh the temp of the water in the pipes will not be warm enough to overcome your heat loss. Ufh only works in houses that have a low heat demand. 

[psirus]

20 hours ago, Declan52 said:

The heat will still rise, physics not much you can do about that, but with the extra insulation it won't be escaping. You will then end up with not needing as much heat. 

You will find that with ufh the temp of the water in the pipes will not be warm enough to overcome your heat loss. Ufh only works in houses that have a low heat demand. 

 

I am not really expecting the UFH to overcome the heat loss from the roof all I really want is the bottom half of the room to be a comfortable temperature.  Would my plan achieve that?  I am still keeping the radiators for days when it's really cold.  My basic thinking is that for the heat to be lost out of the roof then it would first have to pass the comfort zone I am after.  Granted the system would not be able to turn off if the heat lost is too great from the roof.

 

Just trying to decide if it's worth doing from a comfort perspective.  Would 30mm of insulation allow the 46mm of screeds thermal mass to create a comfortable temperature in the bottom half of the room?  Or would I lose too much heat into the floor?

 

There are lot of retro fit systems out there that just sit on top of the floor and don't even have any screed for thermal mass which made me think my plan would at least get some ways towards the benefits of a real UFH install.

 

If its just a case of it will cost more to run because of the 30mm floor insulation but still get the same comfort benefit as if I had 100mm floor insulation then I think I would probably just go for it.

 

If its a case of the heat output will be terrible and mostly lost into the floor and I wont be really any warmer then I might wait a few years and just dig up the floor entirely.

 

Thanks for taking the time to read my posts and guide me to the right decision.

 

 

 

 

Edited July 29, 2020 by psirus

[psirus]

20 hours ago, JFDIY said:

Cemfloor quote that you can go as thin as 25mm over heating pipes if that helps.

 

See also webber 4310 as a member on here said you could do 30mm including pipes

 

https://forum.buildhub.org.uk/topic/13427-col57-introduction/

 

 

If reducing the screed (and thermal mass) and adding a little extra insulation would give a better end result then I would be interested is those liquid screed solutions, thanks for highlighting them.

Edited July 29, 2020 by psirus

[Declan52]

1 hour ago, psirus said:

 

I am not really expecting the UFH to overcome the heat loss from the roof all I really want is the bottom half of the room to be a comfortable temperature.  Would my plan achieve that?  I am still keeping the radiators for days when it's really cold.  My basic thinking is that for the heat to be lost out of the roof then it would first have to pass the comfort zone I am after.  Granted the system would not be able to turn off if the heat lost is too great from the roof.

 

Just trying to decide if it's worth doing from a comfort perspective.  Would 30mm of insulation allow the 46mm of screeds thermal mass to create a comfortable temperature in the bottom half of the room?  Or would I lose too much heat into the floor?

 

There are lot of retro fit systems out there that just sit on top of the floor and don't even have any screed for thermal mass which made me think my plan would at least get some ways towards the benefits of a real UFH install.

 

If its just a case of it will cost more to run because of the 30mm floor insulation but still get the same comfort benefit as if I had 100mm floor insulation then I think I would probably just go for it.

 

If its a case of the heat output will be terrible and mostly lost into the floor and I wont be really any warmer then I might wait a few years and just dig up the floor entirely.

 

Thanks for taking the time to read my posts and guide me to the right decision.

 

 

 

 

The bottom half won't get warm though as the heat will continue to rise up and go out. 

The rads will have water approx 70 degrees, maybe even warmer, going round them giving out a fair bit of heat. The ufh will have water no more than 40 degrees, can be a tiny bit more but will depend on what you are using as a floor covering. That's the issue. If the rads can't heat it then the ufh will have no chance. 

Could you try a fan on the ceiling to try to get the hot air to circulate a bit more. Would be a simple fairly cheap option.

[psirus]

So assuming I add 100mm of insulated plasterboard as you suggested, would my UFH spec be good enough?  I would most likely be happy to add the PIR to the roof but this would come at a later date.  Right now the decision to remove the screed and install UFH is blocking progress so need to make a decision if I should do it or not.

[JFDIY]

Having UFH can only help, and our experience is if you put your feet on the warm floor you actually don't mind the room temp being a bit cooler. Insulation below the screed and in the ceiling will also help. Make sure the pipe spacing of the UFH is quite tight (150mm or less) to help with the vaulted ceiling loss

 

Worst case is that if it doesn't work then you re-instate the rads, or leave them in for this winter and see how you go before removing them?

[Declan52]

You need to work out your heat demand  taking into account the insulation in the walls, roof, floor and the u value of your Windows and doors. This will give you a figure to which you will be able to see if the heat produced by ufh for that area is enough to heat that room.

 

[Russell griffiths]

Have you considered just chucking in a woodburner on that brick wall, how many months of the year is it uncomfortable in there. 

[Nickfromwales]

7 hours ago, psirus said:

I am not really expecting the UFH to overcome the heat loss from the roof all I really want is the bottom half of the room to be a comfortable temperature.  Would my plan achieve that?  I am still keeping the radiators for days when it's really cold.  My basic thinking is that for the heat to be lost out of the roof then it would first have to pass the comfort zone I am after.  Granted the system would not be able to turn off if the heat lost is too great from the roof.

 

Just trying to decide if it's worth doing from a comfort perspective.  Would 30mm of insulation allow the 46mm of screeds thermal mass to create a comfortable temperature in the bottom half of the room?  Or would I lose too much heat into the floor?

 

There are lot of retro fit systems out there that just sit on top of the floor and don't even have any screed for thermal mass which made me think my plan would at least get some ways towards the benefits of a real UFH install.

 

If its just a case of it will cost more to run because of the 30mm floor insulation but still get the same comfort benefit as if I had 100mm floor insulation then I think I would probably just go for it.

 

If its a case of the heat output will be terrible and mostly lost into the floor and I wont be really any warmer then I might wait a few years and just dig up the floor entirely.

 

Thanks for taking the time to read my posts and guide me to the right decision.

Ok.

If it's directly on top of an insulated solid concrete slab, like 150mm of it, it will still work. I know, because I have done it ( back in the day when I was wet behind the ears, and the customer was 'always right' and it wasn't worth arguing...). That system is still in and working to this day, and is the only heat source for the ground floor. Is it efficient? No. Is it economical to run? I very much doubt it. Does it take a long time to heat up? Yes, but it also takes a long time to cool down so not the end of the world when you get used to its traits.

 

The overlay systems work. they're just expensive for what they are.

 

Your solution will certainly achieve what you are looking, for just on this forum we are all advocates of "fabric first" approach and advise as best we can to reduce heating needs vs increase the number of rads etc. So, that's where the resistance is coming from.

So, if you have 60mm - 30mm PIR - 30mm of UFH pipes buried in liquid screed, what is going on top? I would seriously recommend a bonded engineered wooden floor or tiles as that will add to the thermal inertia and help with the way heat is injected into the floor and emitted into the room.

My observations are that you are OK to accept some compromise here on running costs, as you don't envisage using it all year round to heat the room, and nor will it be the primary heat source ( at least until you see how the UFH performs without the rads ), so if you are asking id this approach will do WHAT YOU ASK FOR then the answer is 100% yes. You will feel the difference for sure, and the fact that you'll have a mix of rads and UFH on the same ground floor will help with any short cycling issues from the boiler. Don't ever dream of running this UFH on it's own as your boiler will hate you for it.

 

FWIW I would use 12mm pipe here and run it at 100mm centres. That will give more volume for screed and greater total pipe surface area to conduct heat. You'll likely need 2 or 3 loops to make up the one 'zone' to ensure equal temperatures throughout the floor, so as to effectively offset how quickly the heat will dissipate from the smaller pipe.

Bottom line is, it will work.

[psirus]

On 29/07/2020 at 19:13, Nickfromwales said:

Ok.

If it's directly on top of an insulated solid concrete slab, like 150mm of it, it will still work. I know, because I have done it ( back in the day when I was wet behind the ears, and the customer was 'always right' and it wasn't worth arguing...). That system is still in and working to this day, and is the only heat source for the ground floor. Is it efficient? No. Is it economical to run? I very much doubt it. Does it take a long time to heat up? Yes, but it also takes a long time to cool down so not the end of the world when you get used to its traits.

 

It wouldn't be sitting on top of an insulated slab.  Its a 1970s house with zero floor insulation.

 

 

I think after all of the comments and I am going to scale back this project and only fit UFH in 2 of the smaller rooms which are currently being renovated.  Rather than just remove the screed I will take out the whole slab and start the floor from scratch.  The manifold will be in an empty room so I don't mind leaving the floor and pipes exposed here so that I can add UFH to the other rooms at a later date.

 

I am thinking 10mm type 1, 150mm PIR and 50mm liquid screed over the UFH pipes.  Should I add more insulation to the floor or is 150mm enough?

 

The big radiators in the living/dinning room area only have 8mm pipes going to them for reasons only the previous owners and explain.  I will fit 15mm pipes to them and that should help things this winter.  Hopefully next year I will be in a position to extend the UFH into this space.

 

Edited August 3, 2020 by psirus

[Declan52]

Don't forget edge insulation so your slab doesn't touch the wall.