# Key Post: Underfloor heating and wooden floors



## sueellen (28 May 2004)

I have underfloor heating under a concrete screed. A semi-solid oak floor is going on top, the wood will be glued down. I was wondering if anyone knows which adhesive to use. 

I was going to use something called 'gutoid' but am not sure if it is suitable for my circumstances after a chance conversation in my local hardware shop today.

Any thoughts would be appreciated, carpenter coming tomorrow and panic now setting in......

Thanks in advance, woody.


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## sueellen (28 May 2004)

*Re: underfloor heating and wooden floors*





The search facility on this site [broken link removed] might help.

Good luck with your search.

P.S.  There are also a few other threads on wooden floors on this Homes/Gardens section which might be worth a read if you do not find anything in the above.


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## woody (28 May 2004)

*underfloor heating and wooden floors*

Thanks for the links sueellen.


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## heinbloed (29 May 2004)

*maybe to late*

Your underfloor heating in the screed won't work after you have covered it with timber .Except you turn the temperature up and that will burst the timber of due to differences in the expansion....You should have thought about it before:either screed or timber .


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## Bobby (29 May 2004)

*Re: maybe to late*

Heinbloed, could you kindly explain why;


> Your underfloor heating in the screed won't work after you have covered it with timber


I always thought timber flooring was fine, albeit not as good a conducter of heat as tiles for example.


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## heinbloed (30 May 2004)

*maybe to late*

Each layer of material has to be penetrated by the heat.The more layers you have the higher the resistance.Like wearing several layers of clothing.You have 1.)the pipe
        2.) the screed
        3.)the glue
        4.)the timber
Qualpex recommends only the direct fixing of timber on to the pipes with the aid of heat reflector metal sheeting.Check their web page.Putting a third layer -timber,rugs or carpet-will insulate the floor so much that hardly any heat gets through.The user will try to eliminate that by turning up the running temperature.That will be costly since underfloor heating systems are only competitive -money wise-when they have a low running temperature.The different expansion (with heat and moisture )of different materials will cause stress on the connection,the glue.In my opinion this will inevitable lead to break the glue or the materials attached to it. 
With heat conduction it is the same as with noise conduction:the more layers of different materials you have the more difficult it is to get through.At least the breaking could have been avoided by nailing or screwing the timber on battens than would have been laid into the still soft screed.But therefore the screed would have to be a.)thicker ,by the strength of the batons
          b.)reinforced with mesh to avoid the timber batons breaking the screed.
I hope it works out any how.Start to heat up very slowly, not increasing the circulating temperature by more than one degrees C per day -to be set on the boiler,not the room thermostat.If you have to go over 40 degrees to get the room warm it will very critical.Try to keep the heat loss at a minimum,insulate well,check the windows,keep the doors closed.
Has the manufacturer of the heating system given you any advice,guarantee?Has he shown you the drawings?The heat demand/output calculations ? What running temperature are  the calculations based on?Again,I hope it works out.


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## woody (30 May 2004)

*Maybe too late*

Hi Heinbloed,

I did think about this much earlier and was assured by the u.f.h. company at the time the heating system was purchased that wooden flooring installed in this way would be just fine....silly me to believe them.

We have tiled all but three floors, in your opinion would it make any sense to return the wooden floors now and tile the remaining floors?

At this stage of our self-build I must say that I am sorry we chose u.f.h. at all. I think the system is better suited to climates where there are more distinct seasons. In the past week there have been a couple of evenings when I've had to turn the central heating on for a little while ( we are still in our 'old' house). I don't think this will be an option in our new house because of the response times with the u.f.h.

With the benefit of hindsight I think I would be inclined to go with conventional radiators and use the money we spent on the u.f.h. to upgrade the insulation used in the house, (walls, windows etc.). In the long run I think this would provide a more comfortable and 'greener' house. I would advise anyone thinking of u.f.h. to think very carefully, I personally think it is not all it is cracked up to be.

Finally Heinbloed, I have read many of your previous posts and you have certainly given me food for thought with your well thought opinions on environmental issues. 

Thanks.


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## Heinbloed (31 May 2004)

*maybe*

Don't worry to much before you have tried it out.If you still have the choice to go for the tiles than do it.Living with UFH is different from the rads or the open fire.You get used to it like using the tram/LUAS  instead of the bus.The UFH is slower to react so it makes sense to keep it running when leaving the room/house for a while.
The running temperature is so low compared to the rad-system that it is not more expensive/environmental damaging than the using the rads .There are room thermostats available that have timers build in,so you could choose to set the temperature -when you are away for some hours -to go lower during the day but increasing an hour before you come home . Keep in mind that once the room is warm it is entirely warm , not just the area around the radiator.Since you have also insulation in the floor it will keep the warmth much longer,the screed acting as storage as well.With this insulation in the floor you have a better insulated house than most contemporary buildings that have no floor insulation at all.And your new home is probably better positioned to wards the sun than the old one(passive solar heating)
With better windows,more effective boiler etc..If you think that rads are better,after living with the UFH for a season or so ,than you can still return to the radiators.You have plenty of piping in the floor to choose from,so positioning should be no problem.There are sensors available that can sense water pipes through concrete,LIDL sold them for €6 or so,CHADWICKS hires them out.It is a bit dusty to break up a square foot of the screed but much less than chasing a cable.
But try your new home first ,you get used to it.I live with UFH now the first time of my life and I think it is worth it.Running costs are a fraction compered to the standard CH radiators.So I hope it works out for you as well,good luck.


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## XXXAnother PersonXXX (31 May 2004)

*Re: maybe*



> .Running costs are a fraction compered to the standard CH radiators



This isn't the case for everyone. If you are in your house all day, then you might make a saving with UFH (Especially if you are running it from a geothermal system).

However, if you get home in the evening (after work), you'll want to quickly heat up your house for maybe just a few hours. Radiators will provide heat more quickly and won't have the delay of UFH. You'll use more fuel, but for a shorter period of time.

Consider as well that the climate in Ireland is very changeable. You can have a few cold days, and suddenly a warm day. This isn't ideal for UFH systems.


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## MOB (31 May 2004)

*Re: maybe*

We have UFH and mostly wooden floors.   It works quite well.  Mind you, we are not terribly fond of heat anyway, so the UFH really just takes the chill out of the house for us.  If we get an unexpected cold snap (not that terribly common - perhaps  twice a year),  we light the (woodburning) stove.  This gives a quick blast of heat - quite enough to heat the main living areas.


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## alpha (31 May 2004)

*different opinions*

----
Your underfloor heating in the screed won't work after you have covered it with timber .Except you turn the temperature up and that will burst the timber of due to differences in the expansion....You should have thought about it before:either screed or timber . 
----

Not true...at least in my own case, which is all I can vouch for. Have UFH throughout the house, 5 years now. 70% of house is solid wood, mostly Irish Ash, nailed to battens sunk into the screen. 

Have never had a problem with Heat output or movement in the floorboards. Thermostats in every room control room temp and boiler is set to low temprature.


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## gaf2u (1 Jun 2004)

*Underfloor heating control and timber covering*

Two things worth noting regarding the perceived ineffectiveness of u.f.h.
1) When you have stats in a room (timed as someone mentioned) you select approx 18-20 Celcius for occupancy times and 14-16 Celcius (or cooler in summer if you wish) for vacant periods and leave the system on full time. The benefit is in heating the floor slab /& screed which is act a heat sink and once initially heated require little energy to maintain a stable environmental temperature. A traditional rad system requires tremendous energy to bring a cold water system up to 60-70 Celcius to heat the environment to a comfortable degree once or twice a day. Once you get over the traditional mindset and actually leave the u.f.h system on full time they are much more efficient - most modern systems also have external temperature compensation built in now too so if there 's a real cold snap the system adjusts accordingly.
2) Timber covering - the most important thing here is to bring the timber into the finished and heated room and leave it sit for about 4 weeks to acclimatise i.e. balance the residual moisture in the timber with the humidity  of the room within which it is to be laid. This will overcome most of you shrinkage and failure problems mentioned. Can be helped additionally by coating/finishing both sides of the timber prior to laying - prevent moisture absorption and also cupping (boards forming a slight U- shape) due to differential expansion of the two sides, top and bottom.
Timber is however an insulator and there's little can be done about that.
Hope this helps


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## heinbloed (1 Jun 2004)

*different opinions ?*

Hi alpha!
Your floor is NAILED to battens as I recommended to woody.So there should be no mechanical  problem as I said.At what temperature have you set the flow temperature?I have solid 22mm Scand. red deal placed on heat deflector sheets,flow temp. set at 40 degrees (if it gets very cold -5 times this winter-I turn it up to 42 degrees.Return temp. is 5 degrees lower,35 resp. 37 degrees.It would be interesting -not only to me I suppose-
to see how other systems perform.Thanks.
And to gaf2u:
I followed the advice and unwrapped the Scand.pine.They came in packs of 5 planks directly from Sweden and where chamber dried to a moisture content of 8-12%.And than the surprise:the planks took up moisture from the Irish  air and swell ! I did not realise until they where all in place.I run out of planks and ordered more  but this time I had no time for to get them acclimatised, took them out of the plastic wrapper and screwed the straight to the beams.When I turned on the heating the first time the first batch of Scand.pine did shrink-not much,I would say about 1mm per 11.4cm plank-whilst the new planks which where taken straight out of the packet did not shrink at all !
So it depends on the quality of timber that is bought.Kiln dried to 8-12% and wrapped needs no acclimatisation.One never stops learning....


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## Alpha (1 Jun 2004)

*settings*

HeinBloed, sorry missed that detail about nailing to battens. Even with this method you run the risk of shrinkage/expansion of boards causing warps. To overcome this I had all the timber stored in the house with the heat on for about a month before they were fixed. I also had the heat on (very low) for a while before the timber arrived to ensure the screed and the wall plaster were well dried out. 

I don't know that temperature the water is flowing through the system. Same boiler is providing domestic hot water and the temp dial on the boiler is turned well down.

I have stats in every room controlling room temperature with occupied rooms set at 20C (or 17C for unoccupied times). For the majority of the summer system will not even come on and so boiler is supplying domestic hot water only. 

System is supplied by a company called Polytherm. (No affiliation apart from as a customer) 

One other aspect to be aware of. In your kitchen ensure that the heating pipes do not run under your presses. The rising heat can cause food stored in those presses to go off very fast. Like wise don't have them running under Fridge/Freezer or they will be working overtime. If the system was properly designed this shouldn't be an issue.


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## heinbloed (2 Jun 2004)

*settings*

Thanks Alpha!
I followed the advice not to bury any pipes under the kitchen counter/fridge which seems logical when one thinks about it.Do you have a "mixing valve" installed that mixes the returning water from the UFH with the hot water from the flow/boiler to get a somewhat lower temperature than the temperature which is necessary to provide domestic hot water ? If not than it would be an option to save energy/money without loosing on comfort .
What would be your advise to woody ? Should he go for the timber floor or should he tile it since he has the screed already in place-without the battens?


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## Floater (2 Jun 2004)

*UFH & timber*

Is it a workable option to have a semi-solid timber floor floating, or would the necessary underlay type foam be too much of an insulator?


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## heinbloed (3 Jun 2004)

*UFH and timberfloor*

Yes,in my opinion it would be.Usually the manufacturer of the UFH will do a heat input/heat output calculation for you,no problem for him ,with the suitable computerprogramm a question of minutes.Qualpex was very effective with the calculations in my case,everything worked as predicted.Other manufacturers are able to do such a calculation as well.


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## Alpha (3 Jun 2004)

*My tuppence worth*

Tiled floors are the most effective in terms of heat transfer but I think that outside of Bathrooms, Kitchens utility rooms and entrance halls they are too 'hard' for the general living space. (Purely a personal choice)

I would have worries about gluing the floor in terms of fumes and chemicals given off over the years. No basis in fact for that opinion just my feeling.

I think the semi solidor a laminate floating floor is probably the best option for woody at this stage of his build.


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## kfpg1 (25 Jan 2005)

*Advice for Fixing Timber Floors with UFH*

Some great info in this but I will soon be in the position of installing UFH myself and would appreciate peoples comments and how I summarise the story so far.

Best Option = Tiles
Second Best = Timber Floor

If tiling use flexible adhesive & don't 'comb' the glue as this creates air gaps

If timber there are a number of fixing options

Best Option = Use Heat Diffuser Plates
Second Best = Sink timber battens into screed and nail timber to them
Third Best = Glue timber directly to surface of screed
Fourth Best = Put a floating floor down on a layer of insulating foam

Questions arising...
1.Do the preferences for fixing stay the same (assuming they are correct) whether the timber is a. solid b. semi solid c. cheaper laminate?

2.Can anyone give a direct link to the Qualpex page on heat diffuser plates - I can't find it

3.If using heat diffuser plate what do the timber boards get fixed to?

4.If using timber battens what is the best way to get them in place - is it set them out at correct spacings and correct levels positioned just above the ufh pipe circuits then pour in the screed until it reaches the top edge of the battens ??

5.Using glue sounds a reasonable option to me because

a. it eliminates the cost of buying and hassle of setting out the battens

b. glue could be spread so that it takes out some of the variations in surface level of finished screed

c. flexible glue can cope with movement due to expansion

d. yes it is another layer for heat to penetrate but so are the battens - I realise the glue covers everywhere but it is very thin whereas battens whilst at defined spaces are much thicker than the glue (my point is that wherever there is a batten is also an additional barrier to heat along with floor board itself - that is assuming I am correct in thinking that the battens sit above as opposed to alongside the ufh pipe)

Sorry its so long - hope for some feedback on any section of this.


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## heinbloed1 (26 Jan 2005)

*ufh+timberfloor*

Hi kfpg1!
I can't find the relevant Qalpex site neither.If you phone them they will send you a quotation for your job incl.drawings(www.qpl.ie).
There are some other manufacturers out there as well using heat deflector sheets,for example www.nu-heat.com.
I think Unipipe presented heat deflector sheets as well at the Dublin house and home exhibition.
If using tiling then go for cement based glue on concrete floor.The floor expands as much as the glue as the tile,they have about the same expanding factor.The Romans used UFH in combination with cement floor and tiles and mosaic,they are still standing.And these "causticums"-as the UFH was called at the time(cement is "caustic"!)- where running on much higher temperatures than our modern UFH's,more than 100 degrees.The romans used hot air/smoke from killns under the floor at the side of the house.The system as we have nowadays was not known/in use at the time because they had neither electric pumps nor cheap piping material.In some places where they had access to natural hot springs they made use of them,but in the bath and not in their  homes,it would have been to damp.So channels where build in the floor and walls guiding the smoke,leaving the building via chimneys set along the top of the walls.And they did not use much steel in building either(price!) so these floors where very heavy,at least a foot thick.So  high temperatures and plenty of  time was the solution for the idle class.The slaves they kept where working 24 hour shifts during winter.And they had to clean the causticum as well from soot and ash whilst they where still hot,cooling down the heating would have caused whipping at least.  
Diffuser plates are laid between the joists on insulation sheets.The insulation sheets would be between the joists.The floor planks will be screwed to the joists.There should be no gap between the floor planks and the diffuser plates,if necessary any gap must be filled by putting some sheeting(thin timber,strips of ply board,rigid cardboard etc,)between the diffuser plate and the insulation sheet .So the diffuser plates are in direct 
contact with the floor board.
Again:using ceramic tiles and timber floor within the same heating system is technically possible,but more expensive to run.Since the flow temperature would have to be set much higher thanks to the insulating effect of the cement screed plus glue plus tile.Lets say you want the ceramic floor to be warm at 8 in the morning than heating would start at 4,so the timber(equipped with diffuser sheets)  would be warm at 6 and the ceramic at 8,leaving you with the unnecessary bill of heating the timber floor for two hours.The same goes backward,the storage capacity of the heavy stone would allow you to reduce the temperature at 22 in the evening keeping it's temperature for an other 1 or 2 hours.The timber floor would be cold by than.You could overcome this by fixing electric timers for each zone ,but these must be set in advance.... Take the resistance into account.The thicker the material the longer it takes to get the heat from one side to the other.The timber floor would be warm whilst the stone floor would still be cold.Qualpex claims that using heat deflector sheets will bring the warm-up time to about the same level as a radiator system.Which is not correct ,but it is certainly faster than without the diffusers.
Laminate is a better insulator than standard timber(several layers of different materials).But there are as well special laminates available designed for UFH,for a special price of course.Unipipe showed some at the above mentioned show.As far as I remember the price was a good deal above €40 per square meter.
So,this was a long one as well.Excuse my historical spin off.


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## SelfBuilt (6 Jan 2006)

*Re: >>Underfloor heating and wooden floors*

Wayyyyy too late but I did exactly the same as you, semi sold (Bruce) oak flooring and the guys (professionals) used gutoid. Excellent job. Very happy.


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## First-timer (26 Sep 2007)

As name suggests I am a first time poster of a question so if I'm not doing this right, forgive me....
I am re-doing my apartment and want to get rid of the existing very ugly storage heating in the living room, kitchen and hall.  I have found two alternative electric underfloor heating systems - Devi and Ecofilm set.  Has anyone ever laid either of these and if so what's the verdict.  
I am planning a semi solid floor over them and I want to make the right choice.  This heating will be the only heat source for the kitchen, living room and hall so it has to work!
Thanks


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## Seans Dad (26 Sep 2007)

I also have underfloor heating under a concrete screed.  I am contemplating using a solid wood floor and gluing it directly on to the concrete. This thread has only mentioned semi solid flooring being used with UFH, is it possible to use Solid Wood flooring and if it is do you have to go with a specilaist type like Junckers


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## mystry4all (15 Nov 2009)

Hi,

I want to have underfloor heating like the cables are fitted in the cement....The cement layer will be digged and the cables will lay in it.....Is that possible?


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