Raft foundation- no insulation - UFH?

[sandingdog]

Hi all

newbie question:

I am renovating a 70s property that turns out to have a raft foundation, its at least 300 thick, and reinforced.
We wanted to dig up floor, insulate and install UFH in a new screed, but its not possible now.
I still want an ASHP in the property. Installer has suggested using these polystyrene foil backed UFH overlay panels. We would lose some height but.

My main question is - surely this would be less efficient than just having the ASHP driving radiators?

I know these are insulated, but surely a lot of heat is going to sink into this massive uninsulated slab.

At least if there were radiators, the heat would rise up into the room rather than in contact with this huge slab.

Engineer says UFH is better since flow temp can be lower, and that makes it more efficient.

Surely any gain would be lost into this massive slab.

thanks in advance

 

[Notch7]

You need some proper calculations done to get an answer

I know from customer feedback that any underfloor heating on existing old uninsulated floor slabs ends up not being very successful. mostly it’s people adding electric heating mat under tiles in say a kitchen.

Engineer says UFH is better since flow temp can be lower, and that makes it more efficient

So can radiators.

But to be fair volume of water in system is critical, volumiser vessel can help as well as big radiators.

If you have too small a volume the system can short cycle too much

Underfloor heating pipes generally have more water volume than equivalent rads.

Surely any gain would be lost into this massive slab

I think so too

Of course the floor slab will act as a thermal bridge even with just radiators….so an insinuated slab is a drag on the system whatever you do

 

[trojanhawrs]

You could build up ~6 inches if you were willing to lose the height. Would also mean refitting doors and probably electrics/plumbing though.

 

[Why Not Indeed]

At least having a barely insulated slab sinking much of the output of your ASHP means you won't need to worry about it being oversized

 

[dilalio]

Do a proper heat loss calculation.

Look at Heat Engineer and pay for a one off calc.