I was wondering about retro-fitting underfloor heating to my house and am interested to know peoples opinions about the practicality of this ? The house was built in 1980 and has a concrete floor downstairs and normal chipboard on beams for the top floor. Is it a practila matter to chip away channels in the concrete and run the pipes in those then re-screed over the top ? Any ideas about how much that might cost for 50 sqm of downstairs floor area ? Also, I've heard references to the amount of insulation being needed below the heting pipes, would a 1980s house have been built with enough below the floor ? How does this apply to the top floor ?
There are foam slabs with built-in grooves for the pipes to lay over an existing floor. See Speedfit and Polyplum for the kits.
Best draughtproof your house and pack it with insulation - 15-18 inches in the loft. Seal the loft with a silicon gun. Sealed hatch door. Insulated outer doors. underground insulation against the foundations. Then no need for UFH.
No, daft idea. You need a good slab of insulation under the pipes to minimize heat loss into the ground. Your channel plan would lose heat sideways and then into the ground.
No, probably none at all.
The other problem is the hest output per sq. m. is limited and because the wall and glazing insulation isn't so good in old houses, you can't get adequate heat out of UFH without having the floor surface too hot.
Thanks for the replies, I alsoi am curious about UFH for the first floor which is a normal wooden (chipboard) floor suspended on beams. Is there any way of retro-fitting UFH to this type of floor ?
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Mike saying something like:
If you want to do it properly, you'd have to lift the flooring and put down 6" of insulation, then heat spreader plates, lay the pipes in, then lay the floor again. A quick and dirty way of doing it would be to use pre-routed boards [1], lay them on top of the existing floor, lay the pipes in and cover them with more chipboard. You have to be bloody careful you don't drive a screw through a pipe, but that's a normal concern for this type of UFH. You'd nearly treble the weight of the floor though and lose at least
1.5" of height, necessitating cutting your door bottoms, etc.
[1] Instead of pre-routed boards, you could clip the UFH pipe to the existing floor in the necessary pattern and then fill in with chipboard.
Thanks for the replies. Is it normal for UFH for each floor to have a single giant heating pipe circuit or is it more normal for each room to have its own set of pipes and temperature controlled valves, kind of like a big underfloor radiator per room ?
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Mike saying something like:
Have a look here...
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the second part of your question is the answer - each room is a seperate entity, connected back at the manifold, but part of the zone. There's a limit to the size of the individual loops - about 15~20sqM, so a bedroom generally won't push the limit. Small rooms may be combined, as you suggest above. Each zone would be fed from and back to a manifold, the supply to each manifold being controlled by a zone valve to suit time of day, demand for heat from stat, etc. Within the zone would be the downstairs rooms or the upstairs bedrooms, and so on. The return water from the UFH zones is blended with the incoming hot water to cool it to an acceptable temperature for UFH.
There's no limit to how much control you put on it - you could have, if you wanted, individual control of bedroom temperature, with the addition of stats and zone valves for each room, but that's a bit overkill. I've never tried a thermostatic valve on the input to a room UFH, but I see no reason why it wouldn't work - just a question of mounting the valve with an input pipe to and from it.
It's a very effective system and perfectly suited to lower-temp inputs like ground heat recovery or solar heat banks, but running it off an oil or gas boiler can be expensive - not that it needs to be pricey, just that it can be.
I'm thinking of one I did a couple of years ago - 60sqM of UFH in a barn conversion - cost an arm and leg to run over the winter, but the owner was pushing 90 and felt the cold. It was a beautiful job, but there was nothing I could do if he insisted on having it on all the time. Besides, the old bugger was loaded and could well afford it.
A Keston Qudos boiler with integral outside weather compensation can be used. Have a primary loop top the manifold(s). Have a high limit stat on this loop, set to 55C to protect the UFH pipes. Then set the weather compensator curve to give no more than 50C max and the system runs itself. The Keston has a directly attached cylinder stat that will run the boiler to maximum temperature when DHW is called. A three-way "divertor" valve should be used to divert the water from the boiler to the rapid heat recovery coil cylinder, or DHW heat bank, preferably a direct model. Also Keston make a combi version of the boiler. So when DHW is called no heat to the UFH and instant DHW at the taps. then it reverts back to the UFH when taps are off.
The great thing about this system is that no blending valves need be at the manifold(s). The manifolds can be made up of cheap 2-port zone valves operated by local room stats. Or no zone valves at all and a central room stat or sensor) that modulates teh boiler (UFH) temperature down, or boiler off. Only one pump is needed. It is a very cheap and effective system. The weather compensator on the boiler ensures the right UFH temperature. Centrral romm temperature control or individual room or zone control.
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