Heating and cooling: Wooden floors and UFH - with ref to wood types

1 to 15 of 15

- CommentAuthorLandsrud
- CommentTimeJan 23rd 2016
Hello,

We installed UFH in both bathrooms in or 1830 wooden house in Norway. Down stairs we tiled, but when we came to tile the up-stairs we suddenly thought why not just use a wooden floor as this room isn't going to be a true wet room (even though its wet room tanked). I did a bit of research and found out that placing UFH under wooden floors is possible but depends on the type of wood, for example soft woods like pine might form a insulating barrier and the heating effect would be lost. What are people thoughts on this? Any advise on wood types and thickness. I have read the flor thickness should not be more than 14mm(?)
- CommentAuthorcjard
- CommentTimeJan 23rd 2016
It'll be fine, just turn up the flow temperature a little. its ten times more thermally resistive than tile, but you should get at least 30w per sq m at a 40degree flow temp and 200 centres
- CommentAuthorjamesingram
- CommentTimeJan 24th 2016
Stick some insulation in between the joists below the pipes it'll most travel up then
- CommentAuthorTimber
- CommentTimeJan 26th 2016
Softwood has a thermal conductivity of around 0.13W/mK. Hardwood 0.18 W/mK.

Both should be fine, but make sure you use narrow boards which are dried down to a low moisture content before fitting to reduce the risk of distortion.
- CommentAuthorcjard
- CommentTimeJan 27th 2016
<blockquote><cite>Posted By: jamesingram</cite>Stick some insulation in between the joists below the pipes it'll most travel up then</blockquote>

See, I always wondered about that. Where else would it go, even in a free void? Heat rises. Even if the ufh heated the air, to the PB of he ceiling below (which is allays warmed by the downstairs ufh too) the heat would just rise to be at the top of the floor void and heat the wood anyway. I was never quite sure why I put wool in the void for heat purposes.. I've done it for sound more than anything
- CommentAuthorSimon Still
- CommentTimeJan 27th 2016
Hot air rises, not "heat". Without insulation the air in the void will heat both the floor above and the ceiling below. The ceiling will act heat the room below - Presumably not as effectively as ufh but would still have an effect.

If it's your own house and that room is also heated it probably makes little difference. If it's a room you don't use or heat at different times you might.
- CommentAuthorVictorianeco
- CommentTimeJan 27th 2016
I've used 1" ply as advised previously on here and then tiled on top. Don't bother!! No heat is getting into the room.

I/m considering taking up the ply and using some kind of cement board? Can anyone advise?
- CommentAuthorSimon Still
- CommentTimeJan 27th 2016
Our bathroom floors are

- 22mm Eggerboard structural flooring
- http://www.wundatrade.co.uk/overfloor-heating/381-composite-overfloor-panel.html Fermacell panels through which the UFH pipe runs
- Schluter Ditra uncoupling matting

then tiles. we're running the UFH as very low temperatures so normally you don't notice the floor being particularly warm but when I accidentally reset the boiler to the default settings it was definitely transferring heat.

UFH suppliers normally warn that you need additional heat sources in bathrooms as they tend to be small and the bath/shower/toilet mean the amount of pipe to room is low. Our top bathroom has external flat roof, an external wall and a rooflight and it's the coldest room in the house (19C rather than 20C - not much but it would be better to have it a degree warmer). Cable is there for a towel radiator if required - will be interesting to see how it copes when we have a proper cold spell
- CommentAuthorNick Parsons
- CommentTimeJan 27th 2016
VE said:

''I've used 1" ply as advised previously on here and then tiled on top. Don't bother!! No heat is getting into the room.

I/m considering taking up the ply and using some kind of cement board? Can anyone advise?''

I can't, I am afraid, but I do have a Q: Is the UFH used intermittently, or for long periods/constantly? If the former, I can understand the ply acting as a temporary barrier to heat. If the latter, I cannot. If it's on all the time, the ply will eventually become warm, and cannot help but emit, surely?
- CommentAuthorCWatters
- CommentTimeJan 27th 2016 edited
We have wet UFH under 21mm Engineered Oak (6mm oak on 15mm plywood) in several rooms although not a bathroom. Works ok and warms up quicker than the screed and tile. However it does need higher flow temperatures than screed.

The advantage of using engineered wood is that it is much more stable than solid wood. This means you can afford to risk using wider boards and these look better than narrow ones in my opinion. I think ours are 210mm wide.

The downside is cost. Good quality engineered wood can be more expensive than solid.

If the wood layer is going to be structural (eg it rests on joists rather than screed) I believe it needs to be at least 18mm thick. That might even be in the Building Regs somewhere. I don't think 14mm is thick enough unless over screed. I don't recommend 18mm chipboard AND 14mm engineered wood or laminate.

I'm not sure how well a wood floor would stand up to getting wet regularly. I can see it getting trapped in the joints and causing problems.
- CommentAuthorcjard
- CommentTimeJan 28th 2016 edited
Posted By: Simon StillHot air rises, not "heat". Without insulation the air in the void will heat both the floor above and the ceiling below. The ceiling will act heat the room below - Presumably not as effectively as ufh but would still have an effect.

If it's your own house and that room is also heated it probably makes little difference. If it's a room you don't use or heat at different times you might.

Surely the radiant element is low and it is predominantly convective, which will accumulate in the void at the top and heat the floor?. Ultimately if the ufh runs constantly it will achieve same steady state heat transfer whether insulated or no?
- CommentAuthordjh
- CommentTimeJan 28th 2016
Posted By: cjardSurely the radiant element is low and it is predominantly convective, which will accumulate in the void at the top and heat the floor?.

I'd agree with that.

Ultimately if the ufh runs constantly it will achieve same steady state heat transfer whether insulated or no?

Insulation slows down the heat transfer, so it reduces the power. So the heating won't be as effective unless run at a hotter temperature. It's the same as your roof insulation reducing the heat lost from your house.
- CommentAuthorEd Davies
- CommentTimeJan 28th 2016 edited
Posted By: cjardSurely the radiant element is low and it is predominantly convective
Lots of people seem to assume that but I've yet to see a good justification. I think radiation is of the order of half of the heat transfer, more or less, depending on the geometry, etc.

Ultimately if the ufh runs constantly it will achieve same steady state heat transfer whether insulated or no?
If the UFH supply water is at a constant flow rate and temperature then there's a fixed amount of heat energy going into the floor void. But there isn't a fixed amount going out along the return pipes. If the floor is insulated there will be less heat loss from the water, the return temperature will be higher and the heat flow into the room will be less.
- CommentAuthorSimon Still
- CommentTimeJan 29th 2016
<blockquote><cite>Posted By: Ed Davies</cite><blockquote><cite>Posted By: cjard</cite>Surely the radiant element is low and it is predominantly convective</blockquote>

UFH is usually referred to as radiant (rightly or wrongly)
http://www.healthyheating.com/Radiant_Mythology/Radiant_Floor_Heating_Myths_.htm#.

A bit of guesswork but...
If you had UFH pipes running in the ceiling void it's a fairly small, enclosed space.
The pipes would first heat the air on the void. Being small/enclosed that would quickly reach an even temperature (or at least the differential between top and bottom would be low).
The hot air in the void then heats the floor above and the ceiling below via conduction.
The floor and ceiling then heat the respective rooms via radiation/convection

Insulation slows the heat flow (but doesn't completely prevent it) in one direction in the same way it does In any other situation.
- CommentAuthorEd Davies
- CommentTimeJan 29th 2016
Nice reference Simon, thanks:

â€œRadiant floor heating and radiant ceiling cooling exchange between 50% and 60% of the energy via radiation ergo they, by ASHRAE definition are radiant systems.â€

Backs up my calculations of about 50% each for radiation and conduction/convection: http://edavies.me.uk/2014/08/radiators/

Of course, both of those are for the floor surface whereas here we're discussing heat moving from the pipe to the void around it. My guess would be that with a pipe which is more exposed to airflow upwards convection would be a larger proportion but radiation, including radiation downwards, would still play a significant part.

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