Floors dug up - should we put in underfloor heating??

[houseonahill]

We are in the middle of some major renovations in our house which include excavation of most of the ground floor to put in a new subfloor, DPM, insulation and screed. Had arranged with builders to put radiators in place but the whole time I've been wondering if we should add underfloor heating pipes...

The thing is, we can't afford the full system (manifold and controls etc) right now. Our budget is maxed out. But we could probably stretch to the pipes / staples / edge insulation to get them in place for the future.

I'm not desperate to have underfloor heating right now but I *am* thinking about the possibility that in the future we'll switch from gas combi to heat pump (honestly, could be 10-15 years away) in which case UFH might come in handy. However, I've read you can get away with slightly oversized radiators as well (and we've installed some of those already).

Current state of floor by the way is, in order from top to bottom:

1. Slip layer
2. 100mm foil-surface rigid insulation boards
3. Radon / DPM barrier
4. 100mm concrete
5. Radon / DPM barrier
6. Gravel

So my questions are:

A) Is it worth slapping those pipes down now, even though we can't connect, test or use the system at present, just for future-proofing? Or is UFH really not the be-all and end-all here?

B) If your answer to A) is "yes" then is it necessary to install edge insulation down to the level of the floor insulation, as in this picture, or can it be installed above that level to form a perimeter around the screed layer only? We also have excess of the DPM / slip layer poking up the sides to form a basin at present - and uneven bare brick / DPC line in the wall behind. So am not sure how I'd stick the edge insulation neatly to that. But is it doable?

 

[Schrayder]

Edited

 

[Madrab]

Yes, if you can stretch to have it laid, if UFH is a possibility in the future. It's a much more efficient way of space heating. Just need to decide on where the manifold would go when fitted in the futre so you can terminate the pipes properly.

 

[Diver Fred]

Yes. definitely get the insulation in, the pipes in, Take lots of photographs of the insulation and pipework.

Change the order of the floor medium if you can to

Top
Finish
UFH pipework in screed
Insulation (the more the better)
Levelling Sand
DPM
Binding sand
Hardcore (Compacted)
Bottom

Get the Kitchen running UFH ASAP - you will never regret it.

Keep receipts and 'photo's for EPC assessor as that will count to the house score.

 

[mattylad]

Insulate well while you can, even if you do not go further with the UFH at least the insulation will help.

 

[MeldrewsMate]

In reality the cost of the UFH manifold will be about the same as for several radiators, their valves, and the pipework to feed them, so my advice is to install the full UFH now. In this way you have the lower running cost savings of UFH, plus the knowledge that it is working, rather than the belief that it will work when you come to rely on it in ten years!
My opinion is that UFH will further develop to include floor temperature sensors within the next 10 years. Presently the most popular are 10 kohm thermistors, though I can't guarantee they'll be the standard in ten years. The idea will be to modulate the floor temperature to match the heat loss from the heated room, alledgedly reducing energy use/pumping power/cost. If you can arrange an internally smooth conduit from the manifold to each heated zone (15mm plastic plumbing pipe as a suggestion) then a replaceable sensor can be pushed into place using, say, 8mm or 10mm plastic pipe as a 'sensor pusher'.

Get as much insulation in as you can now; it's money well spent (and it's cheaper than concrete). I assume the radon barrier is mandated in your area; again though, use this opportunity to dig an extra 50/100 mm and add more insulation....put the extra spoil in the loft - it'll be worth a fortune for use in sea defences in 50 years

 

[muggles]

Agree with MM, installation costs will be similar to radiators and UFH will be much cheaper to run

 

[houseonahill]

Thanks all for these thoughts. A few points:

1. Radiators are already installed, this isn't a question of either or, but going for UFH on top.
2. Would love some thoughts on the point that these pipes will be empty for many years. Is that an issue? What if the pipes have a crack and we don't know because we were never able to test them at the time of laying them down? This really puts me off shoe-horning UFH into our plan, tbh. But I am considering it because of the potential that it might benefit us in the future.
3. The floor layers I list above are newly installed - we can't rearrange them now and there's no opportunity to put more than 100mm insulation in. From what I've read, that's a decent amount, no?
4. Does anyone have any comments re: my question B) ?? If I can't resolve that, I can't go ahead with UFH.

 

[Mr Chibs]

I’m new to ufh,but wouldn’t have radiators now, if it was my choice.

I have 100mm of kingspan under the screed, you can put insulation under the concrete or under the screed. Faster heat up times when under screed.

Perimeter insulation can be on top of floor insulation, put in some ufh roll perimeter foam in as well, this is cheap, and used when the screed expands/contracts.

I fitted my own ufh, so it can be done diy.

Shout if you need more info.

 

[gas112]

just remember underfloor does not have the same response time to heating the room as radiators do it needs to be on a lot longer

 

[winston1]

just remember underfloor does not have the same response time to heating the room as radiators do it needs to be on a lot longer

Indeed so it costs a lot more to run.

 

[Mr Chibs]

No, as it will only be on for a couple of hours per day, the slab Holds the heat most of the day. Also the temperature is a lot lower than running a radiator.

once the slab is warm, you just top it up each day.

At the moment mine is doing once a day in the morning.

It’s a different way of doing the heat, set to temp, and let it do what it wants.

 

[winston1]

The fact is if the slab keeps the house warm when you don’t need it you are wasting energy.

 

[Madrab]

Indeed so it costs a lot more to run

Have to disagree ... UFH is run cooler so use less energy per Kw/h ... it also works on averages ... so it holds the house at a mean average temp and then raises that temp slowly when required rather than cold to hot ... cold to hot as with a normal convection system. The mass also acts as a thermal storage, releasing that energy slowly.

The way it heats the space is much more efficient and minimises drafts and cold spots so the air temp doesn't need to be as warm, as with convection radiators, to actually feel more comfortable, UFH can hold the air temp 1 or 2 degrees cooler than convection rads to 'feel' just as comfortable (an air temp that is run 1 deg cooler can save up to 10% in energy costs) . Radiators use convection so the heat rises to the ceiling and therefore takes more heat to get the air at the user level warm enough, whereas UFH work more on radiation from below and as the heat rises the living level space is kept warmer, again more efficient.

All in all it works out cheaper to run if used properly, has a longer lifespan and doesn't stress the boiler/system components as much.

 

[winston1]

Have to disagree ... UFH is run cooler so use less energy per Kw/h ...

Rubbish. A kW/h is a kW/h whatever temperature it is.