Retrofit underfloor heating

[mdurkin]

All,
Much as I'd love to be designing my own home and starting from scratch I'm not! I'd like to install underfloor heating on the ground floor of our house. The floors are a mix of existing raised timber floors and concrete floors where more recent extensions have been added. One room has a combination of both.
I'd like to install a single UFH system that can be fitted on top of the existing suspended and concrete floors, and must run seamlessly where the two floors meet in our kitchen dining room.
Does anyone have experience of fitting such a system. I'm currently trying to research the options available. These are my main requirements:

Must be a dry install (laid on top of concrete / raised wood floor)
Must be as slim fitting as possibly so the floor height is not significantly affected
Will be a wet pipe system which will connect to a thermal store (I'm currently working on the store spec)
DIY install preferred to keep costs down

I'd be really interested if anyone on the forum has experience with such a system, or even just some suggestions for systems forum members have come across that would be suitable. I've found a handful so far, but am really interested in people's experience of them - how effective they are, how easy to fit, how controlable etc.

Thanks,
Matt

[Amy]

www.Ippec.co.uk

Whilst not as good as a new build, they do retro kits to install in existing situations
Grooved insulation boards for pipe to sit in for concrete floor and grooved ali plate for pipe in suspended floors.

Neither are easy to fit and wont give the same performance as a new build.

[dhaslam]

You could also look at  skirting (or baseboard)  systems.  They are expensive but may work out  cheaper than a retro underfloor job.      If underfloor heating doesn't have any insulation underneath a lot of the heat will be lost into the ground. 

[KLD]

A DIY solution could be this: remove old floor boards, fix battens along lower edge of joists, put ply or OSB boards between joist, rigid insulation bds on top, clip UFH pipes to insulation bds, fill with screed flush with top of joists, put new floor bds down, fully glued and nailed to joists.

The insulation bds help to direct the heat up into the room, and provide an easy surface to clip the the pipes to. The screed acts as thermal mass and heat spreader. To achieve a good thermal bond between floor bds and screed, a fully glued down installation is best. But since the screed only floats between the joists, I'd also nail the bds to the joists.

The biggest snag is with the time required. If you want to install wooden floor boards, then the screed needs to be very dry. With good ventilation that takes about 1 day per millimeter of screed. After that time, you gradually heat the screed up to max temp, cycle down and back up once, and then leave to cool down before installing the floor. With the ply boards as first layer you can at least walk through the room during that time ;-)

I've used this technique in an upstairs room, which has now become our favourite room in the house  

Klaus

[biff]

pretty neat klaus,
               good idea and bound to retain heat for days after the boiler has shut down.
     i seem to remember a system of electro heated fibre which ran at a very low voltage,it was laid under carpet or tiles,wicks sold it and i think b,n,q .the only other alternative is to use a floating floor system. which would reduce hight by 75mm, the beauty of this system is that heavy gauge visqueen is first laid down and up behind the skirting, then the runners2x2", the pipes are cliped to the side of the runners which have temp restraining straps,2l2 is used under the pipes to deflect the heat upwards, then the 50mmpoly is cut and inserted between the remaining spaces between the runners. by now the whole thing is pretty fiddly but once the sheets (8x4 sterling board)go down it becomes firm and solid. its the sheets that hold the runners in place but the runners bind the sheets together en mass.screwing down the sheets has to be very exact,naturally,,skirting traps the edge.
    the inlet and outlet must surface side by side,,this is ideal for a floor ,say,25 x 12 or bigger.it can be zoned with a seperate pump which can mix in cold through a thermo controlled honeywell,any pump you want, grunfosse or anything but the honeywell thermo valve is importand,3 port. with a remote thermo well up the wall to give an acurate reading of room temp. no special pipe,just ordinary 15mm hepworth or qualpex,no connections under the floor,one continious run.i got exellent results with this system one of which is in over 16 years in commercial condidions without a bother,
 just a little planning and you can have an exellent reliable heated floor, might even be worth raising the door heads.
                                           biff.

[EccentricAnomaly]

Before using KLD's method downstairs it might be a good idea to do a condensation risk analysis.  Perhaps that would show that a vapour barrier directly under the floorboards would help.

[KLD]

EA, For once I don't expect that there is a major risk of condensation in the structure. During the heating season, any moisture will be driven out by the increased temperatures in the screed. So, you are left with a summer situation, say a temperature gradient of 10°C across the floor, and therefore relatively small pressures. The screed itself and the foil-backed insulation boards act as vapour barrier. That leaves the joists, and any potential gap between joist and screed. Since the floor boards are glued to the joist, and are most likely tongue and grove boards, the amount of vapour coming in should be minimal.

But by all means, if you have access to someone who could run a condensation risk analysis, go ahead (and report back ;-)

Klaus

[chickensoup]

Klaus,
        Your method seems to be the norm as advised by most UFH manufactureres, none of them suggest using a membrane. I'm pretty certain moisture will find its own way out through gaps under the skirting or out through the crevices along the P.U.  I have just completed a large property with you suggested method, I didn't use any ply as 50mm P.U was strong enough told any weight from the screed and me standing on it too!!

             chicken

[tony.]

arent there aluminium sheets available that you clip the pipe into, to help diffuse the heat.
Im looking at fitting them, from underneath my vestibule floor as the black and white victorian tiles just make it very cold.
Was planning on just extending the flow from the small radiator thats in the same room.


going to fit celotex underneath and silicone it to no gaps

tony

[KLD]

Tony

The spreader plates I've seen so far were all rather thin. I doubt that they will actually spread the heat over a wider area. Also, depending on how good the thermal contact between pipe and floor covering is, you'll need a higher temperature flow through the pipe. So, add as much insulation underneath as you can to accommodate for the increased temperature differential between heated void and cold underfloor area.
Are your tiles installed on top of wooden floorboards? It might be just as effective to hold the pipes against the floorboards with pipe clips, and get the pipes rather closer together than the spreader plates would dictate (maybe as close as 80 or 100mm?). Using 16/2 mm PexAlPex pipe, you can run a maximum of 120m in a single length.

I run the UFH as described above at the same flow temperature as downstairs in a solid floor arrangement (concrete slab -- insulation -- screed with pipes in -- tiles on top). There is a noticeable difference in floor temperature, and in heat output.

Klaus

[EccentricAnomaly]

EA, For once I don't expect that there is a major risk of condensation in the structure. During the heating season, any moisture will be driven out by the increased temperatures in the screed.

Yes, and the direction of out the moisture would be driven in is down into the joist, towards the bottom that's now noticeably colder than it was before the insulation was installed.

[KLD]

Well, that's certainly the case once there is moisture at the height of the screed layer. But, how would it get there? From the room side there is a strong temperature gradient across the floor boards, so there should be no water diffusion going into the structure. Hmm 

Klaus

[EccentricAnomaly]

If there was no vapour flow down into the joists the partial pressure of vapour at the top of the screed would be the same as that in the room (due to diffusion through the boards and flow through any gaps).  Of course, the relative humidity would be lower there due to the higher temperature but that's irrelevant; it's the pressure which pushes the water through.  Only a diffusion of water down into the joists will get rid of the pressure which causes the diffusion you're trying to prevent.

In an uninsulated floor a lot of the vapour will evaporate out of the bottom of the boards and the sides of the joists.  With the insulation in place it can only go out through the (now colder) bottoms of the joists.  Perhaps the use of vapour transparent insulation would be a good idea.  Vapour transparent screed is a little harder to imagine - concrete will let water through, of course, but I think it's a lot slower than softwoods.

[KLD]

EA, okay, I understand. So, we need to either prevent vapour going through the floorboards and reaching the screed, or prevent it going down into the joists from here. In order to preserve the best thermal contact between screed and floorboards, I'd be reluctant to put a membrane in between. One could drape individual strips of membrane across each joist before fixing the support battens along their lower edges, or put a continuous membrane between screed and insulation. Both preferably with a doulbe-sided stickyness on the upper surface of the joist, to seal the penetrations of the floorboard nails. What d'you reckon?

Klaus

[chickensoup]

Does it really matter? once the moisture has evaporated and it will.. pretty rapidly!  the joists and surrounding timber will stay dry....won't it?  Please i need to know more as i don't want any comebacks....well its to friggin late now!

      chicken