Underfloor Heating Advice

[Too Late]

Hi all
A previous house renovation i install UFH on the ground and first floor. I used a typical system where the runs were screeded over and finished with a self levelling compound and tiled.

I am now starting a new renovation, but this house has a concrete slab throughout the ground floor. Thinking i knew best i have got the builder to quote up digging it out, insulating and installing UFH

The difference is a rather costly and i am wondering if technology has moved on, whether or not a low profile UFH on the existing slab is a viable solution.

I dont particularly want to lose head room

Does anyone have any recommendations or thoughts?

Thanks

[Mont Blanc]

I'm not an expert, but from my own experience of fitting this, I think you have answered your own question.

You note that insulate is a key point, and this still stands AFAIK - You still need to have a good depth of insulation underneath the UFH pipework. You can't just put the UFH pipework directly onto the concrete slab as the heat will just be absorbed the wrong way, downwards, into the concrete and large amounts of heat will be wasted.

[Swervin_Mervin]

Mont Blanc said:

I'm not an expert, but from my own experience of fitting this, I think you have answered your own question.

You note that insulate is a key point, and this still stands AFAIK - You still need to have a good depth of insulation underneath the UFH pipework. You can't just put the UFH pipework directly onto the concrete slab as the heat will just be absorbed the wrong way, downwards, into the concrete and large amounts of heat will be wasted.

Apart from the fact that the concrete will act as a huge heat storage battery, and once up to temp won't lose that temp very easily, at which stage the air will heat.

OP - there was a company when I researched this a couple of years ago that could rout existing slabs to take UFH pipes. That could be one fairly cost-effective option. As you say, alternatives might be microbore.

We had a mix of sub-floor types when we did this a few years ago, and when we realised the previous owner had actually battened over the concrete floor and then laid floor on top (very odd and had us all stood there staring at it thinking WTF for a while), we went instead for retaining that setup and installing polypipe insulation between the "joists", into which the UFH pipes could be clipped. Meant that in the properly suspended sections the same routed insulation could be fitted between the proper joists.

[Patio]

Too Late said:

Hi all
A previous house renovation i install UFH on the ground and first floor. I used a typical system where the runs were screeded over and finished with a self levelling compound and tiled.

I am now starting a new renovation, but this house has a concrete slab throughout the ground floor. Thinking i knew best i have got the builder to quote up digging it out, insulating and installing UFH

The difference is a rather costly and i am wondering if technology has moved on, whether or not a low profile UFH on the existing slab is a viable solution.

I dont particularly want to lose head room

Does anyone have any recommendations or thoughts?

Thanks

Polypipe overlay

18mm thick with 12mm pipe

Thin screed over top of go with engineered/laminate finish straight over top

[b14]

You have to bear in mind the cost of smashing up the slab and pouring a new one into this as well - this could be v expensive over and above the cost of install of a retrofitted solution, easily £10k+ even for a smaller house. Buys a lot of additional gas that counters the lack of insulation.

[Too Late]

Thanks for the reply.
You are right, the quant quote for using an overlay system instead of smashing the concrete slab is nearly 20k difference.

It was 10 years ago since i installed wet UFH and decided to follow the same approach. It seems like the low profile UFH will save a huge amount of money and time!

[b14]

In our build just finishing now we were quoted £45k to break up the existing slab and repour with insulation etc. We declined and instead had the JK routed-in flooring system installed with screed and latex on top, before Amtico flooring. The installation was painless - but we've not tested the system yet as the boiler is not yet in. If I remember I'll update this thread once we've got it going!

[Too Late]

b14

Any reason why you went for the routed inlay rather than an low-profile install?

Thanks

[OutInTheShed]

Swervin_Mervin said:

Mont Blanc said:

I'm not an expert, but from my own experience of fitting this, I think you have answered your own question.

You note that insulate is a key point, and this still stands AFAIK - You still need to have a good depth of insulation underneath the UFH pipework. You can't just put the UFH pipework directly onto the concrete slab as the heat will just be absorbed the wrong way, downwards, into the concrete and large amounts of heat will be wasted.

Apart from the fact that the concrete will act as a huge heat storage battery, and once up to temp won't lose that temp very easily, at which stage the air will heat.

OP - there was a company when I researched this a couple of years ago that could rout existing slabs to take UFH pipes. That could be one fairly cost-effective option. As you say, alternatives might be microbore.

We had a mix of sub-floor types when we did this a few years ago, and when we realised the previous owner had actually battened over the concrete floor and then laid floor on top (very odd and had us all stood there staring at it thinking WTF for a while), we went instead for retaining that setup and installing polypipe insulation between the "joists", into which the UFH pipes could be clipped. Meant that in the properly suspended sections the same routed insulation could be fitted between the proper joists.

I'd like to hope that there are people about who could quantify how much heat you will lose downwards?
I suspect it will depend on a few things including soil, geology, water table etc?

[LooneyTunes]

Are you certain the existing slab isn’t already insulated?

[Kwackersaki]

This lot keep popping up on my Facebook. No idea why, but they seem to promote its suitability for existing floors.

https://www.wundagroup.com

[LocoBlade]

Before we moved in to our current house I laid low profile UFH across our entire ground floor over a solid uninsulated concrete slab (early '80's built house) and it works really well, definitely one of the best decisions we made.

We used the Wunda foam/foil board system with a thin screed over top and although it works well once installed, installation itself was a bit of a nightmare and I wouldn't recommend it because of that. The adhesives they supply to bond the boards to the concrete floor aren't great and in a couple of rooms we had some boards lifting, causing flex and and cracking the thin ~5mm screed laid over top, Thankfully this became apparent fairly early on before we laid a permanent floor over top and I was able to mechanically fix those areas down with screws and insulation washers using a thermal imaging camera to ensure I was well clear of the pipes! I then put another few mm of thin screed over top to repair it and it's been rock solid since, but if I did it again I'd go for something that lays the pipes in a grid then you pour a thicker 20-30mm screed over it to encapsulate it as I think that's a more robust solution.

Because the pipework is close to the floor surface it responds a lot quicker than a conventional UFH slab but conversely cools down quicker too so you can schedule it in shorter bursts more like radiators if you want to, but a much better way is to ensure your boiler (or heat pump) can modulate itself to low flow temperatures then run the floor pretty much all day every day over winter but at a very low level. To do that you need weather compensation / load compensation along with electronic mixing valves and a heating engineer that actually understands the concept (most don't).

[b14]

Too Late said:

b14

Any reason why you went for the routed inlay rather than an low-profile install?

Thanks

Two things, we didn't want to lose any ceiling height (although in practice that wouldn't have been an issue, looking at the finished product) but mainly as per poster above, the builder wasn't keen on installing it and also was worried about getting a good finish for the Amtico to go down (since it shows every imperfection in the floor it is installed on).

The installation of the routed in system was really impressive, they did a big area and zoned the place with a big manifold, and it all went in in a couple of days. As above though, no idea yet if it's any good! I'd imagine it'll work similar to the poster above, faster responding but not hold as much heat.

[LocoBlade]

b14 said:

The installation of the routed in system was really impressive, they did a big area and zoned the place with a big manifold, and it all went in in a couple of days. As above though, no idea yet if it's any good! I'd imagine it'll work similar to the poster above, faster responding but not hold as much heat.

Yep I got a quote from JK and almost went that direction, the price for the actual routing / pipework was surprisingly cheap and very similar to the Wunda system we ended up with. The main thing that swayed me elsewhere at the time was the quote we had to screed the ground floor afterwards to encapsulate the pipes (nearly £4k for pumped screed about 5mm deep on a ~120sqm area) which added over 50% on top of the cost. In hindsight though we ended up screeding over top of most of the Wunda panels and mixed / laid that ourselves using bags so could have done the same with JK. The other thing I wasn't sure of was the output they quote is about 10% lower than many overboard systems and knowing our slab wasn't insulated with boards I decided to go that route as they do give a bit of thermal separation between the pipework and the slab. I think it's a good system though and if we had an insulated slab it would have been a no brainer.

[LooneyTunes]

Too Late said:

Thanks for the reply.
You are right, the quant quote for using an overlay system instead of smashing the concrete slab is nearly 20k difference.

It was 10 years ago since i installed wet UFH and decided to follow the same approach. It seems like the low profile UFH will save a huge amount of money and time!

That £20k difference isn’t comparing apples with apples. It’s the cost for the massively improved insulation that one system offers and the other doesn’t.

We have just had a low profile overlay board system installed on the first floor of a property. From memory it is using 15mm pipework at 150mm centres into routed boards that are screwed down with a bonded compound over the top.

It is a far thinner installation than the ground floor slab build up (50mm screed over UFH pipework laid on 100mm PIR insulation over 150mm concrete slab) but those routed boards have virtually no insulative properties. They just make the installation easier.

[Too Late]

So update
I have 2 quantity survey quotes for my project
Currently, one with radiators, the other with wet UFH replacing the concrete slab

The difference between the 2 quotes is £61,000

JK have currently quoted £6,164 to route the floor in, run the pipes back to a manifold. Plumbers and electrician will need to do the rest. I am waiting for the quote for the first floor UFH

After a call with JK i am very impressed and i am likely to get them to do my wet UFH

Edited by Too Late on Thursday 3rd October 14:11

[Cheib]

Just going though this…contractors are currently specifying an underfloor heating system. Old house, system will be laid directly on to joists which will have insulation underneath/between. It has taken the builder/heating specialist about two weeks to come up with a system that will provide enough heat and within the constraints of the “build up” given it is an old house so they are working with various fixed thresholds etc.

We will have underfloor heating downstairs and radiators upstairs which are all on individual circuits from a manifold.

Regardless of which system you go for the key thing is making sure the system you go with will be sufficient for whatever the heat loss is that it has to cope with.

Edited by Cheib on Thursday 3rd October 22:21

[OutInTheShed]

Cheib said:

Just going though this…....

Regardless of which system you go for the key thing is making sure the system you go with will be sufficient for whatever the heat loss is that it has to cope with.

Edited by Cheib on Thursday 3rd October 22:21

But what is that heat loss?
You can spec a house to deliver for example a 20degC room temp when it's 0degC outside.
But some people might want 22degC
or you might want to design around worst case weather of -10 with a gale behind it.

There are other variables too, like rate of air change.

You might take your room temp choice as an absolute requirement, or you might take the view that for a few freak days in the average year, you'll either wear 3 fleeces or drag an electric fire out of the loft.

If you're talking about a major refurb, you might be designing around the projections of GW and harder winters ahead while seeking payback over 30 years.

If you're doing a quick cheap job, then you can design around oil boiler flow temps, if you're future proofing you want high COP heat pump flow temps.

There are many trade-offs, cost, payback time, practicality, loss of headroom, restrictions on floor coverings, influence on the way you use the building. You can chase efficiency for its own sake, but will that give you a nice home to live in?

Thing is, you can spend a great deal of money to save another £100 a year on gas or oil.

If someone is telling you the 'heat loss' they 'need', it's best to dig into where that's coming from, because it's really very variable.

[LooneyTunes]

Too Late said:

So update
I have 2 quantity survey quotes for my project
Currently, one with radiators, the other with wet UFH replacing the concrete slab

The difference between the 2 quotes is £61,000

JK have currently quoted £6,164 to route the floor in, run the pipes back to a manifold. Plumbers and electrician will need to do the rest. I am waiting for the quote for the first floor UFH

After a call with JK i am very impressed and i am likely to get them to do my wet UFH

Must be an enormous place for there to be a £60k difference between quotes for different technologies?

With what JK are suggesting, you’ll clearly only have the level of insulation you have in the slab at present.

Cheib said:

Just going though this…contractors are currently specifying an underfloor heating system. Old house, system will be laid directly on to joists which will have insulation underneath/between. It has taken the builder/heating specialist about two weeks to come up with a system that will provide enough heat and within the constraints of the “build up” given it is an old house so they are working with various fixed thresholds etc.

We will have underfloor heating downstairs and radiators upstairs which are all on individual circuits from a manifold.

Bit like where we had routed boards on first floor. The lads who installed ours (who have been doing UFH only for over a decade) went nuts screwing them down. They reckon gluing/leaving them floating is a recipe for disaster.

[Cheib]

OutInTheShed said:

if you're future proofing you want high COP heat pump flow temps.

That’s the route we’ve gone down. We had a dreadful and very expensive to run gas fired central heating system…we’ve have a totally new system currently being installed. An awful lot of work went in to specifying the system (not by me).