I have a large room to screed at work, 75mm celotex with 75mm of screed on top. It's for office and dry storage. Currently there's only electrcity for heating but there's a possibility of ground source heat pump or gas heating in the future (gas main 150 metres away but this is part of a larger development).
Will it be worth embedding UFH pipes in the screed just in case, if so what's the minimimum I can do now? My guess is staple pipes to celotex in 3 loops for zones and terminate them but how? I've been quoted GBP2400 for the installation but the cost of pipes looks like GBP800.
It would have to be a *very* large room to need 800 quid's worth of pipe, even including whatever system you use for holding the pipework in place before screeding. (You can use the sort of giant lego stuff that polyplumb sell, but you'll probably want more than 75mm screed on top, or plastic combs into which the pipes clip and plastic spiked 'U' clips pushed into the insulation below, which you can get from various suppliers including Toolstation and, IIRC, screwfix.
You will need to calculate the heatloss of the room to determine the required heat output of the floor, and from that the pipe spacing. You also need to do mass flow calculations to work out how many parallel loops to divide the UFH into: much over about 10m^2 at 100mm spacing the pressure required to drive the necessary flow of water through the pipework gets more than you can get from a standard circulation pump. Unfortunately the calculations involve non-linear components so you can't simply apply a formula: you need to look up values on a graph (I have an ancient Hepworth one, part of a cyclostyled typescript guide to UFH from back in the 1980s!) but it's not rocket science.
Lastly you need to plan out and actually lay your pipework, which can be a bit fun!
Altogether not a matter of a trivial 'throw a bunch of pipe onto the floor and then screed' operation, but as you have no doubt appraised it's now or never!
No need to do any more than put pipes in, however a manifold may be useful so you can terminate/pressurise them before screeding to test, and prevent crushing.
Lay in concentric spirals at 4" pitch. That gives a very large transfer area - ideal if you only have warm water.
All I used was rebar mesh with the pipes tie wrapped to it. Cheap as chips.
That is unecessary. Simply don't use more than one reel per loop. If that means more reels, use more. I would say at 4" spacing (I used 8", a slight mistake really) you meed a loop for every 7.5 sq meters I had two for 30 squares, and its a bit light on peak power - only about 50W/sq meter.Thinking about that if the pipe spacing is 100mm its effectively doing 10 meters length per square meter floor area, so that looks like a maximum recommended pipe length of 75 meters. IIRC I had 100 meter reels and that was the recommended maximum per loop. I get good flow through 8 (parallel) lengths like that with a standard pump.
Never join pipe either. Throw the scraps away or use them to plumb the house elsewhere.
much over about 10m^2 at 100mm spacing the
Too much detail. stick to 100 meter runs max and less if possible.
It can be that simple actually. But to get the best out of limited lengths, you need to lay in a double spiral So conceptually your hottest flow is nearest the coldest outer wall, and the coldest return is next to that, and you must take that double loop around till you get to the middle where conceptually, the flow and return are joined in a rather messy big loop. Its not good to bend the pipe too hard.
I'll add in a couple of other points: putting heating under things like kitchen cupboards or sofas is a waste of time. The efficiency of the whole thing is the ratio between the insulation downwards, to the cold floor below, and the 'insulation' upwards, into the room. The more carpets and furniture you have, the hotter the floor needs to run and the better the insulation below has to be. UFH works best on conductive floors like tiles, or at a pinch, wood. It suffers from rugs, and is a disaster under thick carpets. If your idea of comfort is a fitted carpet with underlay, forget UFH.
Indeed, £800 is a *lot* of plastic tube and Polypipe egg-boxes. Of course if you're including the manifold etc then a large part of it will be that. The Polyplumb egg-boxes (red plastic former that holds the pipe in place) are wonderful. They are strong enough to walk on, they are easy to work, they hold together well and they hold the pipe in just the right place. I'm sure that it's cheaper to use re-bar and tie wraps but it can't possibly be easier or more satisfying.
I'm with TNP on that, the rules say you mustn't have pipe joins in the screed anyway and 100m is a sensible max length so laying multiple 100m runs works just fine. If you use the PP boxes then the pipes will naturally sit at 100mm spacing which is perfect. If you lay at 100mm spacing you're giving yourself most flexibility. You can always run cooler water if you've got too much heating.
Having done it I can confirm it's one of those jobs which appears to be complex because all of the literature and lots of the people like to make it sound "special". In reality it's trivial - it really is that easy. The only thing I've not seen mentioned here so far and which really does matter is that the pipe must be pressurised during the screeding and must remain so while the screed goes off. This is important because the pipe expands ever so slightly when filled with hot water and screed doesn't like that. By pressurising during screeding you ensure there is space for that expansion without cracking the screed.
Just connect to mains water: it'll be higher pressure than the UFH will normally run at. (If the mains were stupidly high, like 6-7 bar, rather than the 3.5 bar that's typical round here, I'd pressurise to less.)
The manifold is external. If you're just putting in the pipework for future-proofing you don't need to bother with a manifold until when/if you want to use the system.
But it might be worth checking the layout of the flows/returns on the maifold so the pipes can come out of the floor in a sensible order in relation to where they need to be in the floor and to connect to the maifold. But that could just be my dislike of "rats nests". B-)
I filled mine with water and pressurised it to 8 bar with a Rothenburger pump. This was through the manifold as a connections test. Manifold about a metre above the floor, watch out not to kink the pipe as it goes through the 90 deg. to the floor - smooth curve former recommended. After an hour I lowered the pressure to 6 bar until after the screed was laid. The pressure protects against builders boots as well as kinks and makes sure the screed doesn't crack. The pressure was removed 24 hours after the screen was laid. Screed finished with travertine. 3 years later, still in love with my floor, sometimes I lay down and cuddle it.
I didn't pressurise mine. 85mm of dryish screed though. No signs of cracking or other problems... yet:-)
I put the manifold on the wall behind what may be some kitchen units.
I have some photos. I opted for 200mm spacing as there did not seem much likelihood of future heat pump water.
My mistake was in allowing a plumber to lay the *eggshells* and do an initial pipe layout. In a single space there should not be a problem but the *interlocking* nature of the pipe spacers prevents one from doing two rooms and expecting a neat lap where they meet.
As TNP says, you must use the 100mm spacing in a double helix for the low water temperatures of green heat and don't try to turn plastic pipe in 100mm for the final loop. Use flexible ducting where the pipes enter the screed and when going through walls. I found doing a paper trial layout essential.
Just for completeness, that's Nooooooooooooooooooooo! because it would be bloody dangerous, you can store a lot of energy as compressed air in 100m of
15mm pipe. Sudden uncontrolled reslease of that energy would be exciting.
No need to hire a pump. Screwfix and others sell a "dry pressure test kit" for about £20, essentially it's a 15mm Speedfit with a Schreader valve and a pressure meter. You fill the pipe with water (easiest is to flush it through from the mains) then connect the ends together with a 15mm T with the pressure test kit on one leg of the T. Pump it up with a bike pump and you can hold it at any pressure you want. The more air you leave in the pipe the more you have to pump and the more control you have over the pressure.
Easy, see above.
Polyplumb have some good photos in their brochures which should give you an idea of how a finished installation should look.
Calvin Sambrook wibbled on Monday 22 March 2010 12:00
Overlooking the problems re: hanging pictures[1], it would be an intriguing to consider UFH in the surface of a wall, assuming the wall is either internal or well insulated.
Seeing as someone mentioned large area low temp rads a while back. Wonder if anyone has ever done this?
[1] If the pipe is foil coated or has a tracer, judicious use of a metal locator...
I saw the idea on a German manufacturer's website but I forget which one. I used it myself alongside my shower. One wall of my shower is constructed of a 20mm Celotex panel into which I cut small V-shaped grooves and set into those grooves is 10mm speedfit tube. There is a thin plywood panel on top with a large mirror as the visible surface. It's run as a circuit off my underfloor heating.
I must admit I didn't do this in order to make a radiator, the bathroom almost has the opposite problem of too much heat as I really want the towel rail on to make the towels all nice and cosy even when the room is already warm enough. With one whole wall of the shower a mirror I was looking for a way to keep it clear of condensation. It works rather well.
In my case the problem of screwing something in to it was not an issue as no-one would try to drill into a mirror (would they?) but I think it would be a major issue if one were to use the same idea elsewhere.
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