If bedrooms are upstairs Go for radiators. That way you can have a nice warmth (22 degrees) to get up to and not worry about obscuring most of the radiant surface with beds, cupboards etc. as you'd be doing with UFH, and you can have thick luxurious carpet on the floos. UFH in bedrooms is in my mind a complete waste of money and a sub-optimal way of heating bedrooms in which you spend little time awake and should be much cooler during the night anyway.
If the ground floor is joists over a void as I think you mentioned then the floor surface will remain the same height after UFH.
And of course... don't forget you'll still want heated towel radiator things in bathrooms even if you have UFH in them. You absolutely need such items to not only dry damp towels but to hang wet coats/clothes on if you get caught in a shower etc. I have mine spurred off the boiler feed before the 2 way (upstairs/downstairs/both) zone valve. That way it's heated all the time the boiler is running unless both upstairs and downstairs zones are fully satisfied so the boiler is off.
Belated thanks for the new replies: all much appreciated, contrary views and advice and all.
It's clear that proper insulation is the key to success with UFH, but am I right in thinking that however good that insulation is, a large expanse of glass - as with a run of patio doors - is still potentially a localised cold area however successful the heating is overall?
If so (and assuming that it's practical to do so) would running separately-controlled trench radiators along the length of the doors be an effective remedy?
Yes, but also be aware o9f just how much heat UFH can put out with the pipes laid real close. I had a run of about 12 pipes going down a 900mm corridor to various zones. It was like an oven there., Used to have to kick the cats out of the way.
If to have bare tiles or laminate by the window and lay the pipes at something like 100-150 mm centres in a strip along there, you will get a really hot pieces of floor.
BUT my experience of UFH is that is actually reduces draughts hugely. There are normally no hotspots or coldspots so there is little convection and little lateral air movement. And because te floor is warm cold ankle level air is non existent. I used to run the rooms about 1-2 degrees colder than radiators for the same subjective feelings of warmth.
You don't need to do that. Simple increase the pipe density of the UFH in that area.
A low density UFH is around 50W/sq meter with water temps around 50-60C. That's at around 800mm centers. 200W/sq meter is easy, at 200mm centres IIRC and 400W /sq me easily possible. So 2x1 area of floor might be crackling out 800W.
Thats is more than an Aga.
You will find some sites say you shouldnt exceed 100W/sq meter. I say that is utter bullshit. My corridoor was about 5 times that an it didn't crack.
Thanks for those. What I'm slightly concerned about is installing UFH and then discovering that the patio door run still does get appreciably colder than the rest of the open-plan space (perhaps because of heat loss through the framing?)
I was wondering if a belt-and-braces approach installed during construction might be worthwhile insurance.
Is solar gain the result of direct sunlight? The run of doors only receives that in the late afternoon, and even in the hottest weather never becomes noticeably warmer than the rest of the space. But the drop in temperature relative to the rest, even with the current heating system set pretty high, is very marked.
Thanks for that: you're the first person to suggest radiators for upstairs and UFH for the ground floor. Your reasoning makes sense for separate bedrooms though perhaps lass so for a single large open-plan space (bathroom apart) containing just one bed, which is what I'm planning. But I take the point about heating under large items of furniture being redundant and perhaps wasteful.
no, its isn't altogether as bad as it appears. What happens is that locally the floor there doesn't lose heat, but that means it doesn't actually 'steal' the heat from the hot water.
The danger is to be understood more simply. What determines the efficiency is the insulation above to the insulation below ratio.
BUT even if that is bad, the *overall* heat loss is low from that place, and what happens is that the heat transfer to the room (or loss through the floor to underneath is dominated by sections that CAN cool the water BECAUSE they are NOT under furniture.
Or to put it another way, you will only increase unwanted heatloss to the ground underneath, if the actual pipe temperature and screed temperature is increased in that area, and then only by an amount dependent on the insulation under it.
As I said before, have huge amounts of insulation under any screed.
My way of doing the thing was as follows. A concrete slab floor was sanded, then a DPM laid on it, then in my case 50mm of high density polystyrene. Today Id be thinking of 100mm+ and that shuld be laid up the walls as well.
Then we cut reinforcing mesh to fit over that. It's very cheap and helps stop screed cracking.
The UFH pipes were tie wrapped to that. Again, simple and cheaper than the 'custom system', and allows some very tight spacings - IIRC the reinforcing grid was around 100mm grid extent.
The zones were brought back to a manifold, connected and filled with water, then I pressurised the whole thing with a hired pump, top about 3 bar IIRC, and watched for leaks. The pressure was left in for the two days it took to screed the whole ground floor.
Then the wall bits of foam were cut off flush with the screed. After that it was tiling slating and laminate laying time. After a bit of levelling on the screed which was shoddily done as it happened.
Much to my surprise the whole thing performed to spec, and the only mistake I made was sizing the boiler and pipes just big enough to cope with -5C. That left nothing over to get it UP top temperature when it was -5C :except the open fires and the wood burner. But they worked splendidly. Peak output from the main fir probably around 20KW :-)
I'd lay more pipe next time 50W/sq ft is OK for a modern well insulated room if you leave it on all the time, which I ended up doing, but isn't enough for a rapid warm up.
Our bedrooms are all pretty small so single finned radiators still heat up the spaces nicely and eliminate cold zones caused by old double glazed windows whilst running UFH temperatures but for a large open plan type area built to modern spec. I'd go for UFH.
Our between-joists rooms cool quickly enough that I have the heating on right up to around 23:30 at night.
I was also slightly side tracked by the fact our bedrooms are down stairs so UFH would be an in-screed install which would give long warm-up and cool-down times which again in our house, heating bedrooms by radiators is a far better solution to achieve warm go-to-bed and wake-up periods without having a hot bedroom during sleep hours.
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