Morning … moved into a new house about 18 month ago, has underfloor heating in the kitchen and the bathroom upstairs. Kitchen is spot on and the floor gets nice and warm, bathroom floor no where near as warm.
Bathroom floor is tiled, noticed when we viewed the house that there was an odd tile cracked, noticed quite a few more once we’d moved in.
Decided to lift the tiles to re-do them and to investigate the underfloor heating.
Its tiled on top of 18mm T&G boards, the cracks in the tiles where above the joins in the floor boards. With the boards up you can see that the pipes are laid on top of Celotex boards and are sitting in screed.
With the floor boards sitting on the joists theres probably about a 5mm gap between the top of the screed and the bottom of the board, been told having a gap won’t be helping the heat transfer ? I’m also guessing that’s allowing the boards to flex abit causing the tiles to crack?
I’m guessing the 18mm T&G boards aren’t ideal for transferring the heat to the tiles and if theres a gap underneath that’s not gonna help either.
My idea was to drill a good few holes (50mm?) in the boards and add some more screed to fill the gap and for some of the screed to fill the holes (so the heat can transfer through the holes to the tiles?)
Will filling the gap help transfer the heat better?
Will drilling holes in the boards help at all?

Cheers

You need to identify what make of underfloor you have and whether the floor construction you have is suitable.
Sounds a strange floor make up to me, not sure that it is ideal. There are some boards you could use instead of wood that would be much better as they offer some thermal mass

You need to identify what make of underfloor you have and whether the floor construction you have is suitable.
Sounds a strange floor make up to me, not sure that it is ideal. There are some boards you could use instead of wood that would be much better as they offer some thermal mass

Make of underfloor heating? No idea, it just runs straight from the boiler (no separate manifold) and just comes on with the radiators.
I agree it seems far from ideal, but its what we’ve got and not really in a position to rip it all out and start again, don’t want to risk damaging the dining room ceiling beneath either.
When the tiles were down, the heating took the chill off the floor but I wouldn’t say it was warm (like the kitchen is), was just hoping there was some way to improve it slightly while the floor was up.
Cheers

You shouldn’t need to rip it up – there won’t be anything wrong with the pipes. However what you describe on how it’s running sounds a bit unlikely – underfloor heating runs at a much much lower temperature than radiators so there must be some kind of mixer or manifold to lower the water temperature.

Have a look at this –

http://www.theunderfloorheatingstore.com/confused/water-underfloor-heating-for-between-joists-or-suspended-floors

Tiles will crack on a floor if there’s any movement. You could try upping the board to 25mm and/or using an isolation membrane like Schluter Ditra.

Sounds like a bodge! Tiles on screed on insulation would be normal or timber flooring on metal trays holding the pipes between joists on insulation obv. If the underfloor comes direct from the boiler it’s likely too hot unless there is a blending valve somewhere. Any gaps like you describe will reduce effectiveness of the heating. Depending on the floor construction can you not remove the boards and use a proprioroty screed (Isocrete maybe) as it’s thin – in it’s place and tile on that?

I’m far from an expert but just been looking into the layout of the pipes (boiler is in the garage and can trace the pipes along the back wall/kitchen floor). The heating flow pipe comes out of the boiler then splits off into 3 separate pipes each with it’s own zone valve, labelled up as Radiators, Bathroom (UFH) and Kitchen (UFH), I can’t see any other type of valve (or anything else) in the pipework before it goes into the wall/kitchen floor. All 3 pipes ‘feel’ the same temperature.
By the sounds of it this isn’t the correct way, and if anything the water feeding into the UFH is to hot?
The UFH in the bathroom is only about 1.5m2 at the most. I’ve just lifted a couple of boards at one end at the minuet (Loo will need to come out to get the rest up) but from what i’ve seen there is Celotex boards (sitting on batons?) then the screed (set hard like concrete) with the pipes running in it.
Increasing the boards to 25mm will make it more sturdy for the tiles, but surely there would be even less heat getting through to the tiles above?
Not sure if I could do away with the boards and just have the screed directly on top, not sure how sturdy the rest of the floor is?
I’m guessing its the wooden boards thats blocking the heat from coming through to the tiles? or the heat is just vanishing into the rest of the floor space between the joists?

Cheers

As said above you should have a valve that mixes water from the Return pipe with the Flow to achieve 40deg water under the floor max. I started with 12mm ply on top of my screed as I was going to lay engineered oak above. Ended up lifting the ply and laying more screed instead, then the oak.

Sorry to hijack this thread but the wife wants underfloor heating in the kitchen where there is currently no heating at all. I can’t see that hot water pipes can be laid without digging up the concrete floor or raising the floor level and causing a trip hazard. Can an electric system be installed? What about insulating the concrete floor so we do benefit from the heating system and not just heating up the concrete slab?

sounds dodgy. As above, the temperature of UFH should be below 50, normally below 45 flow. If it is hotter this could crack tiles due to expansion. Realistically you will only get something around 50w/m2 through the buildup, not very much and unlikely to be enough unless the building is very new. I would be tempted to get rid of it and get a towel radiator if you have the space.

swoosh you are correct you will ned to raise the floor as you need insulation and pipes above the slab. Electric will be very expensive to run

If they are standard tile backer boards then most are insulating, you don’t want them on top of UF heating.
There are some that aren’t insulating such as Knauf Brio , they work well on top as a base for tiles

As others have said sounds like a total lash and the only way to do something about it is to do it properly as you will be bodging a bodge.

Do it properly or put up with the problems.

Also I think it might be harmful to have to hot a floor temp for underfloor but can’t remember why just that it should be avoided.

Bear – it’s H&S innit. Floor has a legal max temp of 29degrees C or it contravenes building regs. If someone elderly collapses on a hotter floor they’ll cook/dehydrate.

I’m guessing its the wooden boards thats blocking the heat from coming through to the tiles? or the heat is just vanishing into the rest of the floor space between the joists?

Check that link I posted earlier. It doesn’t sound like your construction is too unusual – it’s one of the ways that supplier proposes. An air gaps not going to help though so you some sort of screed (or even just sand) to fill that up under the wood. Wood isn’t an ideal covering for UFH but can be used – we’ve got UFH under 20mm engineered boards. It slows down the heat transfer though .

UFH really doesn’t work well if you try to use it like radiators. It should run at a low temperature for longer rather than giving short, hight temperature, bursts of heat like radiators. It works better in a well insulated house.

Sounds like you’ve got a buscuit/pug screed system. Which is the cheapest most effective way of doing an underfloor system in a suspended floor. If its done correctly.

A 5mm air gap isnt going to help things the screen is just an 8:1 dry mix of sand an cement but I think you should be ripping the t&g up topping up and then laying some 19/22mm hardiefloor.

It will help the heat transfer as well as allowing you to tile directly on to the floor.

You do need to look for a mixing valve as the high temperature coyld be causing the tiles to lift. You can run up to 55c most high limit stats on underfloor are at 60c and polypipewont guarantee their systems below 45c.

polypipewont guarantee their systems below 45c.

above?

don’t want to risk damaging the dining room ceiling beneath either

so this is on the first floor?

No Simon. Below, I was surprised as well. I think pipe in screed would work fone though imho. But I was pricing a job whee they wanted overlay upstairs but on am air source heat pump. Polypipe said all there systems where tested above 45c and that what there data is based on.

To tell the truth I have there overlay system at home and it doesnt seem to work below 45c even on the tiles which I genuinley thought it would

Cheers for all the replies guys.
I borrowed a temperature probe from work today, checked it on each of the 3 feeds from the zone valves just before the pipework (white pipe – polypipe?) goes into the wall / floor, all 3 where around 48 to 50 degrees, so it does seem that the UFH runs at the same temp as the radiators !!
I also checked the kitchen floor and that was between 34 to 36 degrees, the bathroom floor (without the tiles) was around 22 to 24 degrees !!
I’ve never had UFH before so just assumed it was all as warm as the kitchen is, hence why I was thinking the bathroom floor wasn’t very warm … i’m guessing the bathroom floor being around 22 to 24 degrees isn’t bad for UFH?
Other than the cracked tiles in the bathroom (caused by heat? flexing boards?) we haven’t had any issues with the heating at all in the 18 month we’ve been in, and I think the whole system has been fitted for around 6 year. By the sounds of it the way its plumbed in isn’t ideal? But is it going to come to any harm the way it is? Whats the worst than can happen?
Cheers

No Simon. Below, I was surprised as well. I think pipe in screed would work fone though imho. But I was pricing a job whee they wanted overlay upstairs but on am air source heat pump. Polypipe said all there systems where tested above 45c and that what there data is based on.

To tell the truth I have there overlay system at home and it doesnt seem to work below 45c even on the tiles which I genuinley thought it would

Ok – we’ve built a ‘very low energy’ house and installed UFH throughout. In concrete on the ground floor but Wundafloor overlay system on the upper floors (pipe in cement board under tiles/pipe in acoustic board under engineered wood). Connected to a gas boiler but running at very low temperatures on a weather compensation driven heating curve. Flow temperature is a minimum of 21C at 12C external up to about 28C around external 0C. It’s working fine. Only when it’s close to freezing outside do the concrete or tiled floors feel noticeably warm to walk on.