What UFH temp for engineered wooden floor

[Adsibob]

We have wooden floor going down on two subfloors, both of which have independently zoned UFH. The engineered boards have a manufacturer’s recommendation that the wood should not be exposed to a temperature greater than 27C. 

Q1:

On the ground floor this wood is being laid in one room where we have a sand and cement screed subfloor. The room in question has its own dedicated manifold so we can set the temp and flow specifically for that finish. What UFH temp would you recommend for that manifold so that the wood is not heated above 27C? The screed is about 70mm thick and insulated by 100mm of PIR. House is not a passive house, but fairly well insulated upgrade from a 1930s semi. Pipes are 16mm thick and laid at 160mm pipe centres. 

 

Q2:

On the first floor, the same wood is going over 5.5mm ply which is laid directly onto 25mm of Cellecta extruded polystyrene that holds the pipes, which is also 150mm laid at 150mm pipe centres. What temperature for this set up?

[SteamyTea]

44 minutes ago, Adsibob said:

wood should not be exposed to a temperature greater than 27C

That implies that the maximum temperature does not exceed 27°C, not that the mean temperature, over the whole wooded area, is 27°C.

Edited December 26, 2021 by SteamyTea

[JohnMo]

Would start with manifold temp at high 20s if the thermostat setting is never reach tweek up a degree or 2.  If you are over shooting the thermostat tweek down a degree or 2, repeat over a few days until you meet the thermostat temp with out overshoot more than a degree.  Leave about 24 hrs between setting changed

Edited December 26, 2021 by JohnMo
Missed words

[JohnMo]

A floor temp of 27 degrees will not be comfortable to walk on

[ProDave]

To get a floor temp of 27 degrees you would need to put very hot water through the pipes.  There will be a temperature gradient from the pipe temperature to the floor surface temperature, and that is hard to predict, but my own heating the UFH temperature is about 35 degrees and the measured floor surface temperature is about 22 degrees.  It will be hotter in places e.g. underneath a rug.

 

Try it and see, starting low and gradually increasing it, and get a cheap IR thermometer to measure it with.

[Adsibob]

So basically there is little to be concerned about because I’m unlikely to reach 27C floor temp?

[Adsibob]

1 hour ago, JohnMo said:

A floor temp of 27 degrees will not be comfortable to walk on

What is considered comfortable?

[Declan52]

You will have to find the balance between how much heat your rooms will loose and how much you can put in via the floor. Start with a temp at the mixer of 35 degrees and see how it copes. If your room never gets warm then you need to increase the flow temp at the manifold until you find that sweet spot. Will take a few attempts to find out so don't stress out to much. Just increase it by 2-3 degrees reach time.

I think 55 degrees is the highest temp you would put into the floor but hopefully you find yours before you get this high.

[Adsibob]

On 26/12/2021 at 17:35, ProDave said:

To get a floor temp of 27 degrees you would need to put very hot water through the pipes.  There will be a temperature gradient from the pipe temperature to the floor surface temperature, and that is hard to predict, but my own heating the UFH temperature is about 35 degrees and the measured floor surface temperature is about 22 degrees.  It will be hotter in places e.g. underneath a rug.

 

Try it and see, starting low and gradually increasing it, and get a cheap IR thermometer to measure it with.

Thanks for everyone’s advice. I have just ordered a laser gun temperature sensor which is apparently accurate to the nearest 0.2C* and will start playing around with it in the New Year. 
 

* Hard to believe as it only cost me £16.89 and there were a couple of other options on Amazon which were slightly more but apparently only accurate to the nearest 2C.

[SteamyTea]

1 hour ago, Adsibob said:

I have just ordered a laser gun temperature sensor

And, at night, you can pretend you are s sniper.

Best buy at Lidl mine was.

That's your neighbour that is, checking up on you.

Edited December 28, 2021 by SteamyTea

[Adsibob]

On 26/12/2021 at 17:35, ProDave said:

To get a floor temp of 27 degrees you would need to put very hot water through the pipes. 

So the manifold was apparently on minimum and we were still getting the plywood subfloor (which is only 5.5mm thick and laid directly over the pipes/insulated Cellecta pipeboards) to reach a temperature of 26.5C on the bits of plywood directly over the loops closest to the manifold. I asked my builder to reduce the temperature and he said that because it was on minimum the only way to do this was to reduce the hot water temperature being sent to the manifold by the boiler. This sounded odd to me, but by the time he had gone down two flights of steps, reduced the boiler output temperature by 2C and climbed back up two flights of steps the temperature of the plywood very close to the manifold had dropped to about 24.8C. The oak flooring is going on top of the plywood and the flooring supplier has said the subfloor (i.e. my 5.5mm ply) should not be allowed to exceed 26C. I'm just wondering if the oak flooring, which is engineered oak and 14mm thick in total, will actually let much heat through when the subfloor it is glued to is only 24.8C. Maybe I should turn the boiler output back up and live with being 0.5C to 1C over the supplier's recommended temp of 26C. But the supplier also recommended we use a thicker sheet of plywood (something like 12mm) and we're using 5.5mm because I thought 12mm would be excessive. It was about 11C outside, so not much of a challenge for the house.

 

The other question I'm wondering is should we have left the temperature output of the boiler as it was (instead of reducing it by a couple of degrees), and just reduced the flow rate instead?

Edited February 8, 2022 by Adsibob

[bassanclan]

Useful little table showing heat output based on different floor coverings and temps 

 

https://underfloorheating1.co.uk/blog/article/Floor_surface_temperatures_when_fitting_underfloor_heating

[Temp]

I'm pretty sure we are running our engineered oak floor quite a bit hotter than the maker specified. Water in the UFH has been as high as 55C but I don't know what the actual floor temperature gets to.

 

It's 18mm engineered oak secret nailed to joists with a wet pipe in foiled insulation UFH system between.

 

 

[Adsibob]

The plot thickens. I spoke to the plumber this morning (who was not on site yesterday when my builder reduced the output temperature of the boiler) and the plumber said that the change my builder made:

• won't have made any difference to the water temp in the floor - because the minimum setting for the manifold blending valve (which we didn't change) is 30C and so whether the manifold was receiving hot water at 65C or 40C, the blending valve will keep the water at 30C; and
• actually cannot be done once we commission our UVC, because we have a low loss header which means we can only have one temperature for the output of the boiler, which must be 65C (builder had reduced this to 40C, but that won't be anywhere close to hot enough for heating the UVC).

So it seems that the "drop" in temperature of about 1.7C that I had recorded must have been a false recording. 

 

On the one hand, I'm starting to wonder if I was foolish to ignore the manufacturer's recommendation that we install a thicker sheet of ply as our barrier between the bottom of the engineered oak and the top of the pipes. I think they recommended 12mm and we went with 5.5mm.  On the other hand, given it's fairly standard for manifolds to have a minimum setting of 30C, and given this was producing a temp of about 26.5C on the bits of plywood directly over the loops closest to the manifold, it must surely be fine as that is only 0.5C over the manufacturer's recommended maximum temp for the subfloor. Surely there is scope for it to get even a degree or two hotter without buckling the oak floor (which in any case has an expansion gap around the perimeter?

 

 

 

[Temp]

4 hours ago, Adsibob said:

On the one hand, I'm starting to wonder if I was foolish to ignore the manufacturer's recommendation that we install a thicker sheet of ply as our barrier between the bottom of the engineered oak and the top of the pipes. I think they recommended 12mm and we went with 5.5mm. 

 

Ideally I would recommend 18-21mm engineered oak is used directly over UFH.

 

I think Building regs require >18mm for a structural floor. Many people buy 14mm engineered oak then discover the 18mm minimum and have to put flooring grade chipboard under it. If they put down 18mm chipboard they end up with 18+14= 32mm of wood over the UFH and I pretty sure that must affect the heat output.

[Adsibob]

6 hours ago, Temp said:

 

Ideally I would recommend 18-21mm engineered oak is used directly over UFH.

 

I think Building regs require >18mm for a structural floor. Many people buy 14mm engineered oak then discover the 18mm minimum and have to put flooring grade chipboard under it. If they put down 18mm chipboard they end up with 18+14= 32mm of wood over the UFH and I pretty sure that must affect the heat output.

We aren’t using our engineered oak as a structural subfloor. Our build up is:

 

1) 14.5mm engineered oak

2) 5.5mm plywood (so the oak is less exposed to heterogenous temperatures from the UFH coils)

3) 25mm Cellecta UFH boards

4) 6mm rubber

5) 22mm structural chipboard

6) posi joists 

 

A very expensive build up, but one that will hopefully be awesome!