Has anyone ever tiled and underfloor heated a suspended timber wooden floor?

[Igletpiglet]

Hallo everyone,
Husband and I are finding it really hard to get info re whether it’s possible to retrofit underfloor heating ( wet or dry) on a suspended wooden floor successfully. 70s house.
Would really appreciate a heads up, positive or negative, from anyone with experience on this, Thankyou ..

We did, but the joists were rotten, so we replaced them, and the floorboards with 18mm Marine ply. The underfloor heating is the electric type, it works well, but you need a radiator as well.

Mittens, Thankyou, did you tile on top? I was wondering about how rigid the ply is above ufh. I am so surprised that you needed a radiator too.

I replaced my entire ground floor with under floor heating on top of the existing floor boards and in the kitchen, I tiled on top of the under floor heating boards. I used a ufh kit from Polyplumb. It connects to the existing central heating with it's own pump and mixer to get the right temperature. It comes with a power lead which plugs into the nearest point. It runs when the central heating runs. I do recommend that a expansion membrane is placed in between the tiles and the ufh boards to stop the tiles cracking as they expand at a different rate. I can send pics if you pm me as I do not have a PC to see the pic attachment button.

Ufh heating takes longer than radiators so I am having my home heating split into two zones so the ufh heating can come on earlier. It works great. However a radiator may be needed like the stairs landing as ufh heat does not travel upstairs so you might need a radiator in the upstairs landing. If you have bay window with uninsulated flat roof, you need to insulate it as otherwise a stratified heating appears with body and head being warm until you stand up. Ufh really meant for well insulated homes which my 1930s is not. This only happens when we have super cold winter but have not experienced it since insulated my bay roof.

We have UFH and no radiators. It does take a few days to warm up after being off completely for months, but then onwards it remains constantly on and gives a wonderful warmth. Ours is wet UFH so cheaper to run. We have a well insulated house though, we haven’t turned the heating on yet.

The good thing about ufh wet heating is that your condensing boiler will always be in condensing mode thus saving you money where as with radiators it will not unless those radiators work with low temperatures like 40c. Most normal radiators work at 75c and the returning water to the boiler is usually ten degrees less. To run in condensing mode, the returning water has to be 54c and below. So another selling scandal from all those heating sales people. Yes, a new boiler is more efficient but will never be the 95% you were sold on for a normal radiator system.

Iglet- we used 10mm marble tiles on the top of it. The electric underfloor heating isn’t as powerful as the wet systems, but they are easier to install - we took the opportunity with installing new joists to lower the floor so there wouldn’t be a step between the hall and the kitchen, so we didn’t want to have a big chunk of wet pipes etc to make another step up

Yep. Wet ufh under suspended floor. The builders made an insulated board layer with batons underneath the joists, then the pipes then more boards to take the weight and then the flooring itself. No radiators. It's toasty warm.

You people rock, this is gold. There is hope! I had really begun to think we weren’t going to be able to do this.
Mittens-such a good idea to drop the floor level a bit while you were at it. Understand what you’re saying re wet vs dry vs output & need for rads. Would never have known that.
Aveabanana- that’s exactly what I needed to know- have the tiles sat in place ok? I have had someone conjuring up stories of tiles lifting you see so that was my exact worry.
Semi- you sound like you need to change your username to ‘properdiyer’ - some amazing advice too- that’s something we def need then, expansion membrane. I’ll pm you my email re pics if that’s still ok. So re boiler- i think you are saying they can handle wet ufh with radiators upstairs ok , but will be running much less efficiently unless you split the heating zones?
Fox- so wet ufh is very doable without rads if insulation is good. Sounds lovely!
THANKYOU all. I am so encouraged. It’s so hard to get independent advice on this so i’m Really really grateful for you sharing your experience.
.

Just remembered as well, for the ufh you put a ‘decoupling membrane’ under the tiles so that they can expand and contract with the heat - it’s the orange bobbly stuff you see in Diy shops - we used a Schluter one.

I beg you not to tile over! Floor can't breathe. We just spent ages hacking off tiles as floor had rotten underneath.

Nearly - that is a good point, we had to add an extra air brick so our floor had sufficient ventilation underneath

Nearly - I think the ventilation that the floor needs is that from underneath though right? So mittens was that air brick for under the suspended floor?

My husband had the thought to fill the whole space in with concrete and rubble, he thinks the builders could sort a damp proof course in but I am not convinced that would marry up with existing wall damp proofing.

Semi and fox, what were your floor finishes?
Banana and mittens, how long have you had your tiles down? Thanks for the membrane advice mittens.

Iglet - the air brick was for the underfloor, we’ve had the tiles down for about 18 months now and haven’t had any problems

yes I suppose our air bricks were also blocked which doesn't help!apologies I'm still slightly reeling from having to hack off ugly tiles and then find rot! I may have a skewed opinion at this current time!

Our floor finishes were engineered wood in some areas, and carpet in others. With both you must ensure the type you use is suitable for UFH, otherwise you’ll lose your heat. Especially make sure any carpet underlay is suitable. We have split heating zones (a heating engineer sorted the plan) and it really is efficient to run. The set up costs were higher though.

Iglet, I have laminated floor boards for the hall and front lounge and tiles in the kitchen. The ufh boards can be tiled on top but required a decoupling membrane. Yes, pm email for pics.

The ufh kit I installed came with it's own pump and mixer to lower central heating radiators temperatures and it has a flow sensor and temperature sensor. It runs when the central heating runs and when the heating temperature reaches 50c plus.