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Message started by Nwekiebrown on Aug 18th, 2018, 2:26pm

Title: Wet Underfloor heating installation (renovation)
Post by Nwekiebrown on Aug 18th, 2018, 2:26pm

Hi all,

I am new to this site.

I am planning on installing Wet UFH in a house I am renovating and want it to be the main source of heating. There will be a radiator in the bathroom and one in the hallway potentially but that's it, I am hoping. The house is a 1920's semi detached property which needs some serious updating. It has a 32kw boiler and cavity wall insulation. I will be putting insulation in the loft as what is in there looks like it was put in by someone who was either blind or blind drunk (I have visions of someone spinning round quickly and letting go of the insulation at random intervals).

I have been doing a quite a bit of research and have come up with the following as my idea. The house has 130mm joists so I am limited in what I can achieve within this.
130mm joists
Space utilised as follows:

25mm x 25mm battens running along the joist bottom.
80mm PIR Insulation laid on top of the battens.
membrane laid over insulation and joists
25mm flowing screed incorporating the 16 or 20mm UFH pipes throughout the house.
This will make use of the 130mm joist space.
On top of this I intend to put 20mm screedboards instead of plywood floor
9mm tiles on top of these (tiles are suitable for UFH).


I have a few questions initially about it before I take my plan any further but more will follow as I get into it, no doubt.

1. Will 80mm of thermal insulation supported by 25mm battens along the bottom of the joists be supportive enough for 25mm of flowing screed on top. It will be poured purely between the joists which are about 350-370mm apart on the ground floor of the house and 130mm deep each. The screed is thinner than is recommended but it will not take much, if any, load as the screedboards will do this on top of the joists.

2. Would 20mm piping make much more of a difference in heat terms compared to 16mm pipe. Both will fit within the 25mm of screed which I am planning to lay on top of the insulation.

3. Would I benefit much from using a bond to "fix" the screed to the screedboards or would this help encourage cracks/splits due to more movement in the screedboards that the screed lying on insulation by itself.

4. Would 20mm screedboard 9mm tiles (few mm for  adhesive) and 25mm screed be sufficient to give a nice even heat across the floor without it being too cold or hot.

5. For best results in heat transmission upward should I ensure a complete layer of adhesive (as much as possible rather than notched) for the tiles so as to remove as much air between the adhesive and tile base as possible. I presume this will make getting them level much harder with a lot less "give" in the tile adhesive.

I apologise if this should go in another forum area but wasn't sure which it should in covering numerous trades.

Title: Re: Wet Underfloor heating installation (renovation)
Post by thescruff on Aug 18th, 2018, 9:06pm

Have to wait till next week for loads of questions.

Really don't like the sound of what you are trying to do.


Title: Re: Wet Underfloor heating installation (renovation)
Post by Lectrician on Aug 19th, 2018, 10:41am

Any reason you're not opting to go for the metal heat spreader plates as opposed to the screed?









This shows your method too, the screed between joists.



https://underfloorheating-direct.com/confused-water-heating-between-joists-245-w.asp

Title: Re: Wet Underfloor heating installation (renovation)
Post by woodsmith on Aug 19th, 2018, 10:43am

If you google suspended floor underfloor heating systems you will find lots of proprietary methods of fitting ufh normally involving fitting a tray to support the pipes and I would recommend using one of these.

I would be interested to know where you found someone recommending pouring screed over insulation wedged between joists, can you post a link?

Title: Re: Wet Underfloor heating installation (renovation)
Post by Newkiebrown on Aug 19th, 2018, 1:21pm

I wanted a longer lasting heat retainer rather than using the plates which then creates an air void to waste some of the heating. That was the only real reason for not going down the plate route. The only people I know that have it installed either have electric for additional heat or in screed which produces a longer lasting heated area. I will find the link and post it when I am back home. Also a lot of the pre-formed systems use a 200mm gap whereas I want a 150mm gap in some areas due to it being the only heat source throughout the house

Title: Re: Wet Underfloor heating installation (renovation)
Post by CWatters on Aug 19th, 2018, 6:39pm

Can you safely tile over the 20mm screedboard? I'd be concerned about it flexing when people walk on it.

Title: Re: Wet Underfloor heating installation (renovation)
Post by thescruff on Aug 19th, 2018, 8:58pm

This is what you should be looking at but you really need to strengthen the joists from above[gallery]thescruff/1534708572.jpg[/gallery]

Title: Re: Wet Underfloor heating installation (renovation)
Post by big_all on Aug 20th, 2018, 12:29am

ok my thought
longer lasting means less efficient
you are far far better without mass to slow down the heating process
in general underfloor needs constant use rather than say 2 cycles a day
if you surround the heating elements in mass you are not warming the room when you need it but sharing the very under powered elements with a mass that will give out heat perhaps 3 or 4 hours after you need  it
there is no way off getting more than 100% off energy back the best way is full heat when you need it in general this is radiators in room not underfloor that unless you house is very very well insulated underfloor is not an sensible option

Title: Re: Wet Underfloor heating installation (renovation)
Post by Newkiebrown on Aug 20th, 2018, 5:16pm

The heating will be on for around 8-12 hours in one cycle a day when needed providing constant heat. Obviously it won't be needed during the summer months just like I haven't used my heating this year in my old house.

I didn't think the screedboards would give much but I will need to check that out if that is the case. They are better conductors of heat than chip/ply which is why I had opted for them but if they're going to cause issues and given their price I might just look at alternatives.

The house is going to be fully insulated throughout and at present only has  2 radiators in the whole house. The house is empty so taking up boards etc. isn't an issue. There was one in the hallway and one in the living room. Upstairs were electric storage heaters which have now been taken out.

Title: Re: Wet Underfloor heating installation (renovation)
Post by woodsmith on Aug 21st, 2018, 8:49am

This plan is just not going to work and will be a disaster if you try to implement it. I don't know where you have seen that you can fill the gap between joists with screed over insulation but I can only think you have misinterpreted their diagrams. Screedboard has absolutely no structural integrity at all and is designed to be fully bonded to a solid surface such as t&g plywood or chipboard, what you are planning is not going to work. If you want this confirmed contact the screedboard technical advice line on 01634296677


Title: Re: Wet Underfloor heating installation (renovation)
Post by Newkiebrown on Aug 21st, 2018, 9:28am

Thanks for this. I did re-look at the screedboard and it appears it is laid on top of OSB which negates the need to have it in the first place. I was hoping to use it instead of ply for the thermal conductivity. Given it would have to go on top of the ply it makes no sense now.

Back to the drawing board it seems but much appreciated for telling me to go have another look, saves me wasting my time and what every little money I seem to have doing up a very old house :(


Title: Re: Wet Underfloor heating installation (renovation)
Post by thescruff on Aug 21st, 2018, 5:08pm

As promised.
130mm joists are not going to take the weight once you start hacking them about to run pipes through, you need the batten on the top to enable you to cross the joists to run the loops between them.

Running a 50mm + screed between the joists was quite common back in the day, however, it gives you a major headache with other services, both installing and access for maintenance.

Pipe size is critical to get the correct heat output, I suggest you contact the supplier who will give you a free floor plan showing the manifolds, pipe lengths, pipe sizes and the number of loops required. In other words, they will design it for you.

I would recommend you use the insulation and floor plates as per my pic, We used Roth products in the pic, one of the best in my opinion but please shop around for the best deals.
https://www.roth-uk.com/en/roth-downloads.php.

Lectrician, has post pics, look at them carefully, you must avoid air gaps as it stops the heat, some are unavoidable.

Big-all post misses the point of underfloor heating which should be designed to run at a constant low-temperature I.E. 42c give or take, any addition radiators or hot water should be zoned separately or combi plus 2 or more heating zones.

I agree with Woodsmith your initial plan would be a disaster, However, with the right screed (lightweight with insulation properties) and strengthen the joists it will work, you still have the other services problem, some of which cannot go in the same screed as underfloor heating.

Any questions please ask

Title: Re: Wet Underfloor heating installation (renovation)
Post by Newkiebrown on Aug 21st, 2018, 9:50pm

As I am also taking out two chimneys and will have around 2000-2500 bricks going spare would it not be an option to support the joists in this way using a honeycomb (or less intensive) support structure to the joists that will enable them to in effect transfer the load to the ground?

I saw this today (link below) showing different warm ups. It shows 4 different set ups and the heat efficiency of all of them with the same parameters.
Obviously they're trying to sell their product but I doubt they can be so misleading as they've stated what they used for comparison. This is what I am obviously, unsuccessfully trying ti get in my home. The bottom left of the two, I.e. using a thinner screed (strengthened) but between the joists using as much of the joists spacing for insulation but leaving enough room for screed. I could go up over the joists a little as long as I then don't have to raise doors and frames.

https://www.youtube.com/watch?v=z75ikxSuTWk

If I am resigned to aluminium spreader plates I might just go back to using radiators as the whole point of the flooring was to have a constant lower heat which the aluminium plates go someway to doing but not like I'd hoped and nowhere near as efficient as I want.

Title: Re: Wet Underfloor heating installation (renovation)
Post by thescruff on Aug 22nd, 2018, 10:17am

A solid mass is always going to be better than the alternative systems.

If you can strengthen the joists (don't forget the DPC) between wall and wood. and you can get around the other services problems, I would say go for a 50mm screed minimum, remember the thicker the mass the longer it holds the heat.

One last hint, tack a DPC to the side of the joists to prevent any expansion noises.

I also suggest a vapour barrier before you lay the finish floor.

Title: Re: Wet Underfloor heating installation (renovation)
Post by Newkiebrown on Aug 23rd, 2018, 5:13pm

Thanks for all the help so far it has made me adjust my plans but it seems I can have a solid mass floor and able to do what I would like to with some alterations.

As for services I am planning to install a full new water pipework system as the one in there is lead piping for about half soldered to copper. I am putting in a new water supply anyway so I have mapped out the water piping system too.

This will run primarily up through the floor once 750mm in from the wall to come up through the floor behind the kitchen units. These run along the sides of two walls. From here I am going to duct it back under the floor through the insulation (where the units are there will be no screed only insulation so I am not heating under units and wasting heat, plus it means units and contents don't get warmed too).
The duct I will pack with something like mineral wool so it's not open and for draughts. The duct will run it on further to the boiler under the staircase. I will also use the same route back for the DHW to the sink.

I am looking into insulation I need if I am to run the cabling for the hob and ovens through the initial duct in the house (the hob and oven are close to where the water supply will come into the house through the wall so it makes sense to use the same duct. As this duct will only carry water supply from outside I am hoping there is very little needs doing for the cabling except for insulating it as a precaution (the water supply pipe will be very well insulated with 32mm Armaflex round it).

It has just had a full rewire which I wish I had waited on as things have had to be moved around the house. But the majority of what has been done needed to be done ASAP as some of the circuitry was from what looked to be the 1920's when the house was built

Title: Re: Wet Underfloor heating installation (renovation)
Post by thescruff on Aug 23rd, 2018, 7:32pm

Ok, but no, gas pipe in the heated floor and if you have to go through the depth, sleeve it.

Title: Re: Wet Underfloor heating installation (renovation)
Post by Newkiebrown on Aug 23rd, 2018, 9:26pm

The gas pipes are out the way and go straight in under the stairs from outside They will be going through the insulation but that's it.

For areas such as under the stairs would you suggest using a cheaper insulation like rockwool as it can fill the full 130mm joist spacing and it's more to limit draughts than anything else as it will be a space that doesn't get used/occupied?

Title: Re: Wet Underfloor heating installation (renovation)
Post by thescruff on Aug 24th, 2018, 7:46am

Personally, I hate Rockwool and would sooner pay a bit extra for Celotex or similar. I'm amazed it hasn't been banned by now.

Cold/unheated spaces leach heat from neighboring areas so need to be calculated for.

Title: Re: Wet Underfloor heating installation (renovation)
Post by Newkiebrown on Aug 24th, 2018, 4:34pm

I've never used it, was just an idea but I had originally planned on using PIR throughout so will continue to do so.

As for no heat I forgot the boiler is in there and so will the underfloor manifold so it will probably be the warmest place in the house :)

Title: Re: Wet Underfloor heating installation (renovation)
Post by thescruff on Aug 24th, 2018, 6:33pm

Lag the pipes, especially the mass of pipes in the floor that comes out of the manifold.

Keep all the loops at much the same length.

Title: Re: Wet Underfloor heating installation (renovation)
Post by big_all on Aug 24th, 2018, 11:51pm


thescruff wrote on Aug 21st, 2018, 5:08pm:
Big-all post misses the point of underfloor heating which should be designed to run at a constant low-temperature I.E. 42c give or take, any addition radiators or hot water should be zoned separately or combi plus 2 or more heating zones.



Any questions please ask


the point i am clumsily trying to make is
underfloor has a greater heat up time so needs to be fully specked and the thermal efficiency off the room is very crutial as is things like open doors and heating off other areas in the house as the heat up time can be hours unlike a radiator for the same situation that can be perhaps half an hour to 40 mins
in general a radiator will give out perhaps 3 or 4 times the heat off an underfloor matt
if the heat input is say 500w an hour and the heat loss is say 350 an hour your heat gain is 150w  an hour so quite slow heating up
where as a radiator for the same situation may be 900w which is less than twice the output but because the heat loss is 350w  the gain is 550w or nearing 4 times the heating rate off the underfloor at least at first when you most need it
and as the heat rises the heating rate improves for a radiator compared to underfloor
indeed if your heating is off for around half the day it may take 2 to 4 hours to get to the level you want dependant on situation
continuos in this situation means on day and night

Title: Re: Wet Underfloor heating installation (renovation)
Post by thescruff on Aug 25th, 2018, 8:27am

BA how are you by the way. Underfloor heating should be designed for a constant temperature with maybe a night set back of say 2-3 degs.

It should be run around 42c unlike radiators 70+c making it safer for kids-babies and at risk grown-ups, you don't program it to come for an hour when you feel chilly, which is why the need for a dedicated underfloor heating zone from the boiler.

I will agree, insulation is important so the more the better, but saying that modern houses are leak proof, at the end of the day a constant temperature of say 21c throughout the building is far better than hot blasts from radiators.


Title: Re: Wet Underfloor heating installation (renovation)
Post by big_all on Aug 25th, 2018, 10:03pm

good as gold scruffs  ;D
hows you ???
have you met ray reardon or len ganley yet  ;D

Title: Re: Wet Underfloor heating installation (renovation)
Post by thescruff on Aug 26th, 2018, 10:27pm

Good Alan Thank You, refereeing Nigel Bond in an exhibition next month. In Yorkshire lol

Title: Re: Wet Underfloor heating installation (renovation)
Post by big_all on Aug 28th, 2018, 1:43am

hes a nipper lol
he come from derbyshire does he not  ;D

Title: Re: Wet Underfloor heating installation (renovation)
Post by thescruff on Aug 28th, 2018, 9:29am

Yes, born in Darley Dale November 15, same day as me  8-)

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