in-ground vs Overlay - Under floor heating

[Ranger 6]

Quite a specific question here - has anyone actually installed/used an in-ground UFH system? One like this where they cut in to your existing concrete floor.



Everything you read says 'don't, there isn't any insulation'. But, I would appreciate opinions from those who have spent their own money - would you do it again?

Context: We had Poly-Pipe overlay installed in the kitchen when our last house was renovated. That was 13 years ago and it worked very well while we lived there. We are now planning a renovation on another house and want to expand the use to the whole ground floor. There's more choice in the overlay sector with very low profile solutions available - approx 1100 sq ft - kitchen-diner, utility, lounge, study, hall & snug.

[toasty]

We haven’t yet but plan to in the next few weeks.

[Happy Jim]

Nearly.

We renovated & extended our place.
The extension had 4” Jablite insulation/4” (might have been less?) concrete/egg crate & poly pipe/4cm flow screed.
The renovation had the existing screed level ( old house, no insulation under the screed/oversite)/minuscule layer of space blanket insulation/egg crate & poly pipe/4cm flow screed.

It all works well enough but the new end of the building needs a lot less time commanding heat compared to the old end.

In winter however you can really see the difference, when it snows half the house has snow all the way up to the walls, half has a 1mr strip of clear pathway ! Heat leakage downwards is a thing!

In short, it’s comfortable, but costs a bit more to run

Jim

[MJNewton]

Happy Jim said:

Heat leakage downwards is a thing!

Absolutely. We often talk of 'heat rising' but that is only applicable with convection in gases (air). Conduction is omnidirectional and will occur down through the earth and sideways through the base of the walls.

[Ranger 6]

Thanks Jim

Toasty - will watch for your experiences

[JackReacher]

Just bumping this tread, as interested in this type of system. We having a small kitchen/diner extension and want underfloor heating. This looks like a good solution for the existing part of the house.

The main issue seems to be inadequate insulation below it, but our house is 2001 concrete suspended floor so there should be a layer of insulation below the screed, although probably not as good as it would ideally be.

Aside from the insulation point, does it risk the strength of the screed?

[toasty]

Well mine is all installed and is working fine.

It does take a while to heat up but stays warm for a long time. Once up to temp, the boiler only kicks in once in a while to top it up.

Any questions, let me know

[ST12AT]

The insulation layer installed below the screed stops hear from going downwards, that’s all.

In a nutshell it works exactly the same with or without, one just costs more to run due to heat loss.

[JackReacher]

toasty said:

Well mine is all installed and is working fine.

It does take a while to heat up but stays warm for a long time. Once up to temp, the boiler only kicks in once in a while to top it up.

Any questions, let me know

Thanks, good to hear. Does your floor have any insulation below it already?

[toasty]

JackReacher said:

toasty said:

Well mine is all installed and is working fine.

It does take a while to heat up but stays warm for a long time. Once up to temp, the boiler only kicks in once in a while to top it up.

Any questions, let me know

Thanks, good to hear. Does your floor have any insulation below it already?

Not as far as I know. The guys just cut grooves in the existing screed.

[caziques]

Just done some grooving in another room of my house (here in NZ). My day job is installing underfloor into new builds.

If there is no insulation keep well away from all outside walls (say 600mm).

As long as you have pipes in the slab it will work - but it does show up just how bad single glazed aluminum windows are.

[dhutch]

Happy Jim said:

In winter however you can really see the difference, when it snows half the house has snow all the way up to the walls, half has a 1mr strip of clear pathway ! Heat leakage downwards is a thing!

In short, it’s comfortable, but costs a bit more to run

That's very interesting.

As suggested, conduction isn't gravity dependant! One option would be to keep a larger margin away from the external walls perhaps. Else if like ours the whole house has solid walls anyway, and we're just planning to do one room for the kitchen floor (rest are suspended with period Oak titles) maybe just suck it up!

Not sure exactly how it relates to windows, I guess you're saying single glazed has no insulation, but also often the windows make a negligible contribution to heat loss as I understand, and it's usually more about avoiding condensation etc.

Daniel

[AW10]

JackReacher said:

Just bumping this tread, as interested in this type of system. We having a small kitchen/diner extension and want underfloor heating. This looks like a good solution for the existing part of the house.

The main issue seems to be inadequate insulation below it, but our house is 2001 concrete suspended floor so there should be a layer of insulation below the screed, although probably not as good as it would ideally be.

Aside from the insulation point, does it risk the strength of the screed?

I installed UFH on the ground floor of a late 80s build house with an uninsulated block and beam floor. It was added onto the existing screed so raised the floor height about 30mm (not a problem as all the rooms were renovated with new doors etc) and the system works a treat. I've done some calculations looking at gas use before and after the UFH install taking into account heating degree days and the gas use isn't much different. I think we put about 50mm of insulation at the edge of the rooms.