Underfloor heating problem - help?

[Iain k]

Hi, I'm hoping someone can help with our issue. We had a heat pump installed which runs upstairs radiators and downstairs underfloor heating (suspended joists). The radiators work great, and the ufh works - but we can't feel it through the floorboards. We have the thinnest laminate flooring I could find but that hasn't helped. Can anyone suggest something to replace the floorboards with that would allow the heat through ( need to keep the floor level the same). The floorboards are the original ones that were put back down over the ufh and are 15mm thick. Thanks 🤞

[Spinny]

Underfloor heating doesn't heat the floor to a high temperature. A lot of floor coverings won't take more than around 26deg Celsius. The general idea is that the warm floor is enough to give some space heating of 50-100watts per sqm. So you are not going to feel it getting 'hot' like a radiator.

 

Do you have a between the joist system using spreader plates under the floor boards ? Hopefully well insulated between the joists under the pipes ?

 

We have a pipe in board system from Omnie where the u/floor heating pipes are sandwiched into the floor board. The lower board is 22mm chipboard routed to take half the pipe, then a top board of 12mm routed to take the upper half of the pipe. The top board is also lined with metal foil to conduct the heat out from the pipe. So that type of system will likely give more output than between the joist with floor boards.

 

Obviously this does raise the floor slightly because 22 + 12 = 34mm which is 19mm higher than a 15mm floor board.

 

Using a heat gun would allow you to measure the temperature of the floor in different places, and compare the temperature when it is on vs the temperature when it is off.

Edited May 26 by Spinny

[Nickfromwales]

37 minutes ago, Iain k said:

Hi, I'm hoping someone can help with our issue. We had a heat pump installed which runs upstairs radiators and downstairs underfloor heating (suspended joists). The radiators work great, and the ufh works - but we can't feel it through the floorboards. We have the thinnest laminate flooring I could find but that hasn't helped. Can anyone suggest something to replace the floorboards with that would allow the heat through ( need to keep the floor level the same). The floorboards are the original ones that were put back down over the ufh and are 15mm thick. Thanks 🤞

Did you have the rads and UFH before, or are they new and were installed by the heat pump company?

[JohnMo]

50 minutes ago, Iain k said:

The radiators work great, and the ufh works

So room temperature are fine?

51 minutes ago, Iain k said:

but we can't feel it through the floorboards

If rooms are warm enough is this an issue? Floor surface temperature is just above room temperature, so well below your body temperature so will always feel cool to touch.

[Iain k]

Thanks for responding so far. This was a system that replaced an old gas boiler and rads. Trouble is, the company that did the installation went bust a couple of months after, so we've had no support. 

The install was insulation between joists then spreader plates above that. The radiators upstairs work great, but the ufh doesn't heat the room - we've left it on for 72hrs + and it made little difference. If you lift a floorboard you can feel the heat - but it isn't enough to heat the rooms. So is there a material that I can put down instead of the boards that may work?

[Spinny]

Think it would be good to measure the actual temperatures so you have some definite facts to work from.

What temperature is the water flow in the underfloor heating pipes ?

What temperature do the spreader plates reach ?

What temperature do the floor boards reach ?

e.g. Search for 'Infrared Thermometer Gun' on Amazon.

Is the underfloor insulation fitted nice and tight and how thick is it ?

 

For a 5m by 4m room, then 50w/sqm is only 1kw. Underfloor heating is best in well insulated houses as you need heat input to meet or exceed losses. In general you are aiming to get the whole space up to temperature and then keep it there, rather than traditional rads at 60C where it can potentially reheat the space within an hour or two.

 

A temperature gun (or thermal camera) would also allow you to look for cold spots.

[Iain k]

Thanks will give that a go. The house is pretty well insulated - under the floor, cavity wall and loft so it should work. However we left the ufh on for 3 days and it couldn't get it much above 16c.

[JohnMo]

Couple things with the UFH 

 

Was there an air gap between the aluminium plates and floorboards? Any gaps acts as insulation so reduced effectiveness.

 

Do you have a drawing of how the UFH was actually done as in the layers from bottom to the finished floor?

 

 

[Iain k]

Not a drawing as such - but photo? 

[ProDave]

That looks to be 200mm spaced pipes.  Fine in a well insulated house like ours, we have 200mm pipe spacing and it works fine, but for a retrofit on an older house I would have expected closer.

 

There is an air gap between the insulation and the spreader plates.  If the detail at the ends of the run is not good, that void could just be full of cold air from under the insulation.  My first thought is lift a floorboard at each end and see if that space is cold, feel for draughts etc.

[JohnMo]

There also looks to be gaps between aluminium plates and the floor boards. This and the things mentioned by @ProDave can all make for poor performance. Requiring high flow temperature to compensate.

[Iain k]

Thanks all for your help, I really appreciate your time & comments.

[Spinny]

Fit seems quite variable, places where it looks OK ish other places where it really doesn't. Some spreader plates bent out of shape, some insulation not well fitted with gaps, and large void under the spreader plates (what proDave says). 

You may be heating the flow of cold air through the subfloor void more than the floor above.

 

If you google between joist underfloor heating images then there are several such systems which have insulation bonded directly to the spreader plates or shaped to fit them exactly which would help to avoid a cold void under the plate sucking out heat.

 

Unfortunately I think it is a job that requires patience and precision to properly separate the cold sub floor air from the warm above floor air. I think I was lucky to have a carpenter fitting my u/floor insulation.

There are also multiple systems on the market, some better designed than others. All too often builders go for what is cheap and immediately available and incentives their interests rather than what is best, especially if the spec is just generic 'between joist'.

[Andehh]

As said above, I would guess that cold air is blowing down the gaps/tunnels moving the warmth out. Trying to go around the edge of the room and use expanding foam to deal the end of each of those tunnels would be a good first step to try I think!

[scottishjohn]

2 hours ago, Andehh said:

As said above, I would guess that cold air is blowing down the gaps/tunnels moving the warmth out. Trying to go around the edge of the room and use expanding foam to deal the end of each of those tunnels would be a good first step to try I think!

I concur habing done a similar job on old house 

you will be loosing the heat to drafts andlack of hard contact to the floor.

the insulation needs to HARD up to thespreader plates and pushing thepiping hard onto the floor 

so no quick fix for this 

rip up floor and do it right 

then you need to balance the flow of the rrads ,cos water will go easiest way --so turning the flow down on them might help as well

thr UFH will never heat up to same as rads  and really rads if are original ones from gas boiler will not be big enough --cos of the reduced flow temp from ASHP--genrally they need to twice as big ,cos tmep from UFH will be around 30 and temp fromgas boiler to rads would be 50+

so they need to be much larger surface area to give same heat pout put

 

Iwould not worry too much onthat at this time 

you need tosort out the downstairs FH problems first  and then later you can maybe chane upstairs

[scottishjohn]

If iwere doing it again iwould use what they have inmy new house for upstairs in your case for all of it

https://theufhgroup.co.uk/products/tekwarm-foiled-400-kpa-ufh-board-1200mm-x-600mm

 

this is covered with t+g cement board , thats the heat sink,then floor covering of choice

total system thickness will be around 40-50mm

mount directly onto your origina lfloor boards 

you will have no air leaks to underside and insulation as well

 and ump the upstairs rads if you want to do it all

you can doall that and still live in the place 

just need to trim your doors 

Edited May 28 by scottishjohn

[scottishjohn]

On 26/05/2025 at 19:41, Spinny said:

Underfloor heating doesn't heat the floor to a high temperature. A lot of floor coverings won't take more than around 26deg Celsius. The general idea is that the warm floor is enough to give some space heating of 50-100watts per sqm. So you are not going to feel it getting 'hot' like a radiator.

Iundertsand what you are sying ,but I can from experince that is not the case

when i did my tero underfloor 25years ago ,very littlechoices and ifno was about

 so I routed all the cipboard floors --1km  of them amdlined the groves with foil and then covered it with 6m ply -to put some strength back in in it

the piping was Keetriple tube --a rubber syatem whereyou have 2 feed pipes and one return all fixed together to make a 10mm thick and 30mm wideassembly 

  Ithen covered underside of floor with space blanket 40mm thick 

asI had spce to get underfloor 

 

--not bad but there were elaks as its just not possible to get it air tight 

 

On top of the floor i use my old axminster carpet --they could not tell me what the tog value --nobody had ever asked that 

even with the underlay it worked--not perfectly but worked ok just took time to vcome through 

 

3 years later i conveted to a tiled floor 

 

the main difference was the speed in the temp change

 In some ways that type of system could be looked on as better ,because you are not heating up a BIG slab then if the days are not consistantly cold you do not get any overheating of house

I know that maybe a novel idea to most --but we live in a country where the daily temps can be totally different ! day to the next 

the upstairs i did what this man has done and it was not a success as hot air leaked out the ends of the joists and keeping it up tight to the floor covering was not good oor easy

at that time i was using a solar thermal cylinder  40 panels along with an lpg boiler 

it worked OK

then later on iwent for an ASHP

which worked out better as I saved the total cpost of the lpg

but In sumatiom Ishould have saved myself alot of grief and fitted and over floor system in the first place.but there were not many out there then  to choose from

 a mistake on my part ishould have gone that way 

 

I still like solar thermal -but the downside is the cost of storag  no problem getting enough hot water for the year --butyou would need a swimming pool in the basement-

kingspan tech calculated for my house ,after giving him all th info that i would need at least 15000litres for it to work  

and that would be 3buffer tnaks with different temp levels to get everything the sun could do through out the day

and building aninsulated tank that big would not be cheap

Idid have some problems caused by lack of storage with the solar--#look at tank temp at 8.00  inthe morning --17c --after running underfloor all night

by lunch time on a summers day the t300litre  tank would boiling ,as i hade specified non regulated vacumn tube

but it just shows there is heat in the sun even in scotland --problem was lack of staged temp storage 

 

[SteamyTea]

Was it a system installed under the MCS?

If so, you may be able to get so redress.

[Iain k]

We did try at the time but as the company went bust, they said we would be right at the back of the queue of creditors...

It's a shame as they'd been going 30 years and and we did do our homework. However, like a fair few other companies they didn't survive the changing of the government schemes in the mid 2010's. Thankfully we have 2 wood burners so we can heat downstairs, but the original cheap laminate flooring I put down to try and help is now looking a bit worn so I thought now is the time to either a) get the original system working or b) bite the bullet & replace it with one that does.