Under Floor Heating

[PetePontoValentino]

HI,

I continue with my house project and am struggling with planning our heating (our main 2021 project).

We will install retro cast iron radiators (water) on the ground floor so that's clear. We are considering using under floor heating on the first and second floors. The plasterboard ceilings are not in a good state so we will remove these, install and replace later. A lot of effort but we also want to preserve the 125 year old chestnut floorboards on the upper floors.

I am a bit nervous about adding underfloor heating (modern technology) under the chestnut boards that I want to preserve. Does anyone have experience of this type of mix. I wouldn't want them to warp or fail in some other way. It might be that they're okay as the wood is very old however, I wouldn't want to spend the money, do the work and find out after the fact that I have made an expensive mess.

Pete

 

[Just4Fun]

I have not done under-floor heating on a large scale, only in a couple of bathrooms and a WC. One bathroom had heating water circulating in pipes I embedded in a concrete floor and the others had electrical heating wire installed in a thin screed above the floorboards and then tiled over.

The electrically-heated bathroom was in a brand new house and it failed within 6 months. I believe the floor dried out and stretched/broke the heating wire. The others have been OK. These are in our current house, which is 120+ years old, so I guess everything was already as dry and settled as it ever will be. No problems with the (softwood) floorboards moving, shrinking or warping.

I assume your under-floor heating will be water-based with heat spreader plates rather than an electrical solution. I have used this approach in another (non-flooring) application. I suggest you put your pipes as close together as the spreader plates allow. This will even out the heat and reduce the required temperature of the circulating water.

I'm not sure how easy it will be to identify the pipe locations from above. Think about that before you cover everything in. If you ever need to drill into the floor you will want to avoid drilling into a pipe.

How thick are your floorboards? Are the rooms carpetted? I think I would mock up an experiment to measure how much heat will actually get through your floors to the rooms above.

Oh, one other thing is to spec everything up carefully before buying anything. I found that commercial heat spreader plates (you could make your own but that is a lot of work) seemed to be sized for unusual sizes of pipe, with 16mm being common here. That means buying pipework designed for the purpose, which can be expensive. For the pipework I put in the concrete bathroom floor I just used a standard coil of plastic pipe from Screwfix which was much cheaper.

 

[gregmcateer]

I installed water-filled UFH over new concrete screed on ground floor extension. On strong advice, I used engineered (ie plywood backed), oak boards to avoid warping, cupping, etc.
Whilst it hasn't warped or cupped, the boards have moved apart in places, despite careful glueing with high quality glue and we don't have the heating particularly hot. I Lifted some at edge and re-glued, but a year later, still some gapping occured. Now resorted to flexible caulk in some gaps, which you can see, but are bearable. (We're not excessively fussy and it is a floor, after all).
Whilst we like having walls clear of rads, tbh, I wouldn't bother with UFH again if the finished surface is going to be wood. If it had been non-engineered, it could have been even worse.
Just my experience, so do seek other views.
Best of luck.
Greg

 

[Doug71]

I have a water UFH system downstairs in my house, most of the floors downstairs are flags or quarry tiles. I like the heat it gives off and I have some really high ceilings so you don't feel the heat is wasted as much as it would be with radiators, plus it's lovely this time of year walking around on a warm floor

The only room that doesn't have a solid floor is the living room, this has engineered oak boards stuck to the screed. This floor never feels as warm underfoot, I always imagine the wood insulates the floor more than the stone so doesn't emit the heat as much. When the heating has been on a few days in this room you can see very slight gaps appear between the engineered boards, I dread to think what would happen with solid wood.

 

[Sandyn]

I wouldn't risk underfloor heating for the very reasons you have stated. Wood is a dynamic product, so a source of direct heat directly below it will do something. Not sure what, but I think the unknown element is very risky.

 

[NormanB]

I do not believe underfloor heating under natural timbers on the first floor is either advisable or even particularly effective. The only exception might be for bathrooms using engineered wood sub floor and ceramic floor tiles which does give some thermal mass. The ideal application for underfloor heating is concrete floor which gives significant thermal mass.

 

[Peter Sefton]

We have wet underfloor heating in our current barn and have had it in our previous two properties with a mix of rads in places. My feeling is underfloor is best on grounds floors in screeds with slate or tile for best effect. We have slate for most of our ground floor, our sitting room has 8" wide Oak flooring stuck down with Sikka Bond, this is 12 years old now with no ill effects but I did ensure the screed had fully cured and the Oak was very dry before laying. We have a couple of ground floor rooms with low tog carpet and this is fine. Our first underfloor heating experience included wet underfloor in the first floor, set in screed under low tog carpet, it was ok but I prefer rads for bedrooms, just giving quick heat up for the few hours a day for getting up in the morning and going to bed.
I would be cautious fitting UFH in an old building under old floor boards, watch out for additional floor weight loading and timber movement, I would stick to rads unless you have a ground source heat pump which works better with low temperature thermal mass of UFH.

 

[Setch]

Having recently ( beginning of first lockdown) had wet UFH installed, and laid bamboo in top, I'd steer well clear of your plan.

The bamboo is more dimensionally stable than most solid woods, and it still shrank significantly after the temperatures dropped and we started using the UFH.

I also ended up lifting the bamboo, having a self levelling screed put down, and refitting the bamboo, and the floor is noticeably warmer as a result, despite being run at a slightly lower temp. The panals the pipe runs in resulted in the pipes being a few mms away from the flooring, and this tiny gap really attenuated the heat delivery. I don't know how you'd avoid this fitting from below, to an existing, not perfectly flat, floor.

 

[PetePontoValentino]

Thank you everyone, I think I will be buying more radiators. That was our original plan and it seems the way to go.
Best regards
Pete

 

[Roberto Flintofski]

You wouldnt put underfloor heating under upper timber floors that may possibly / probably contain wiring too as it will alter the current carrying capacity of the electrical cables I.e. reduce it dramatically with an increase of local ambient temperature

 

[timk5163]

Have you considered skirting board heating, or would this not fit your style requirements? They seem to have the best of both UFH and radiators. I've been looking at DisctreteHeat Thirmaskirt for an integral garage conversion to a living space:
https://www.discreteheat.com/thermaskirt/products-and-information/what-is-thermaskirt.aspxCheers,
Tim K

 

[pe2dave]

Modern house, no 'wood' floors. The guy who installed it said it's a poor solution for wood floors.
Agree, if you value your chestnut, I'd give it a miss?

 

[Spectric]

Underfloor heating always works best when you have the depth to lay it on insulation boards and cover it with a good screed of at least 50mm, it will take longer to warm up but the screed becomes a massive heat reserve and so it becomes very efficient. Correctly designed and installed it will give you good temperature control in each location.

As for traditional Iron rads, I would recomend Castrads | Custom Radiators, Unique Homes and there is a rad builder function on their site that allows you to see what your rad looks like in the given height, width & style.

 

[PetePontoValentino]

Have you considered skirting board heating, or would this not fit your style requirements? They seem to have the best of both UFH and radiators. I've been looking at DisctreteHeat Thirmaskirt for an integral garage conversion to a living space:
https://www.discreteheat.com/thermaskirt/products-and-information/what-is-thermaskirt.aspxCheers,
Tim K

Looks very interesting. The house currently doesn't have skirting board but I intend to fit some too. I like that they include ducting for cabling too
Thank you