Underfloor Heating - embedding UFH in existing concrete or low profile alternatives

[Annas]

Doing a refurb of ground floor of 35yr old build. Knocking down walls opening up some of the back and extending kitchen area in the process. We would like UFH throughout already have some in upstairs bathroom works really well but will need to use different method on ground floor due to not wishing to raise the floor too much.

[JohnMo]

Assume you have zero floor insulation?

 

If so don't do it, you will spend more money heating other things and not the house.

[SteamyTea]

Welcome Annas

 

As a general rule, existing floors do not have enough insulation to take full advantage of UFH, it is the insulation that needs the depth.

 

Have a look around in the specific section on here, there is a lot of information.  Using a Google site search is better that the forum's search.

[Andehh]

As has been said, but worth repeating, insulating insulation insulation! How much depth have you got?

 

If you can fit a 'good' amount of insulation, ie something at 100mm of PIR (or more to make it 'great, but I'm being realistic here based in it being a 35 year old house....) then have a 50 or 60mm screed with pipes in then that's the most efficient way of doing it.

 

If you can't afford 150mm depth for the above, then I'd go with 80mm pir and then an overlay system on top with a self leveller as a compromised solution, but which would work. Quicker warm up and cool down times, and less efficient... But still workable.

[Iceverge]

I stayed over at a mates house recently that was about the same vintage as yours. 

 

I could not believe just how cold the tiled floors were. They were very  uncomfortable under socked feet. Hurt your bones cold. Pain through your knees cold.  I totally get your desire for UFH. 

 

Meanwhile his living room which was wood/laminate was quite ok to walk on despite being, on paper, of a very similar U value. 

 

As said above, the heating losses will be very large unless you dig out the floor and install a chunk of insulation so in order to increase comfort at a fraction of the cost I would consider installing "warm" floor coverings instead.

 

Laminate, LVT, vinyl, carpet, cork, wood are all good options IMO. 

 

 

 

 

 

 

[Temp]

There are several low profile solutions for UFH but unless you have at least 80mm of insulation below the concrete I would avoid them. We have 80mm and wish I had fitted more.

 

If you really want UFH think about taking up the floor. 

 

 

[Annas]

Thanks for the replies. Floor has 25mm of celotex, followed by 100mm of concrete and prob some leveller on top. We are considering  to embed the pipes (in ground UFH) by grinding in to the concrete. Any thoughts?

[Conor]

56 minutes ago, Annas said:

Thanks for the replies. Floor has 25mm of celotex, followed by 100mm of concrete and prob some leveller on top. We are considering  to embed the pipes (in ground UFH) by grinding in to the concrete. Any thoughts?

Don't. It simply won't work. 25mm insulation isn't near enough. You want 150mm. Stick to your existing radiators.

[Annas]

In that it won't be efficient enough or will just not work? The company we're using are obviously fairly sure it will,  have proven track record and excellent reviews - how will it not work?

[SteamyTea]

45 minutes ago, Annas said:

how will it not work?

Basically you will be loosing a lot of energy though the floor and into the ground.

To overcome this, the temperature will have to be higher, this can play havoc with timber/laminate flooring.

But the main thing is it will be wasteful and expensive to run.

You cannot fool nature.

[Iceverge]

1 hour ago, Annas said:

In that it won't be efficient enough or will just not work? The company we're using are obviously fairly sure it will,  have proven track record and excellent reviews - how will it not work?

 

It'll work, but it will cost an absolute fortune to run.

 

You'll have 6 times the advised heat loss through the floor. 

 

Be cautious of reviews, especially ones online. Lots of them are just bought from click farms. 

 

 

2 sensible options.

 

1. Dig out the floor and do it properly. 

2. Stick with rads and use warmer floor coverings for your feet. 

[Annas]

Thanks. We will keep rads upstairs and intend to zone off the UFH downstairs  and run  low but consistently. We also have log burners and will have arga for additional heat if needed. The floors downstairs are not cold - despite there being low insulation in the floor. The company is JK - would be good to know if anyone has used or heard of them? We also have PV panels.

[Conor]

12 hours ago, Annas said:

Thanks. We will keep rads upstairs and intend to zone off the UFH downstairs  and run  low but consistently. We also have log burners and will have arga for additional heat if needed. The floors downstairs are not cold - despite there being low insulation in the floor. The company is JK - would be good to know if anyone has used or heard of them? We also have PV panels.

The company and their reviews are largely irrelevant. Of course they are going to tell you it's going to work, they are trying to get a sale.

 

As other have pointed out, at times you could be sending a significant amount of the heat energy in to the ground.

 

It's an incredible waste of energy and you can't get round the basic physics.

 

However, it would be worth getting a hole drilled to see exactly what is under the slab. You can then calculate the direct heat losses and take it from there.

[Iceverge]

13 hours ago, Annas said:

Thanks. We will keep rads upstairs and intend to zone off the UFH downstairs  and run  low but consistently. We also have log burners and will have arga for additional heat if needed. The floors downstairs are not cold - despite there being low insulation in the floor. The company is JK - would be good to know if anyone has used or heard of them? We also have PV panels.

 

For what specific reason are you hoping to use UFH?

[Beau]

We have just had a heating system installed from scratch. I was keen on UFH to go with the ASHP but the installers were very clear that if we couldn't  fit significant levels of insulation underneath the UFH dont do it. As has been already said it can be made to work but will be inefficient due to heat loss through the floors. We went with rads 

[joth]

13 hours ago, Annas said:

Thanks. We will keep rads upstairs and intend to zone off the UFH downstairs  and run  low but consistently. We also have log burners and will have arga for additional heat if needed. The floors downstairs are not cold - despite there being low insulation in the floor. The company is JK - would be good to know if anyone has used or heard of them? We also have PV panels.

What is the heat source? Gas combi, oil, ASHP?

What are the floor finishes?

 

End of day if you don't care about increased running costs go ahead and install it per contractor's recommendations. It'll take many years of reduced bills for the huge cost of dig out and reinsulate to pay back.

Using minimal floor finish like amtico will promote as much energy as possible to come up into the room, and is less prone to damage from the higher flow temperature you'll need to run.

But keeping with radiators will be much cheaper to run. 

[SteamyTea]

28 minutes ago, joth said:

It'll take many years of reduced bills for the huge cost of dig out and reinsulate to pay back.

We all have a personal responsibility to reduce CO_2e emissions though.

So if there is a more efficient solution, that is the one to take.

[Iceverge]

1 hour ago, SteamyTea said:

We all have a personal responsibility to reduce CO_2e emissions though.

 

True but it reminds me of this. 

 

 

 

 

[Roger440]

21 hours ago, Annas said:

In that it won't be efficient enough or will just not work? The company we're using are obviously fairly sure it will,  have proven track record and excellent reviews - how will it not work?

 

Im in the same position. Without ANY insulation under.

 

I intend to do likewise, just set it into the existing concrete.

 

Of course, its a long way from ideal, it will cost more money to run than if it has proper insulation. Quite a bit more.

 

Its all very well people saying dig up the floor, but that costs. A lot. I ran some crude numbers. Id need to live to well over 100 years old to see payback. Not happening. Got better things to spend my money on.

 

The reality is, its makes no economic sense. Unless you are 12. Dont take my word for it though, crunch the numbers yourself. Use the Jeremy spreadsheet on here to help figure it out.

 

Id imagine with 25mm insulation under, your payback will be even longer.

 

Of course, it will be better done right. If i had unlimited funds id do it right. 

 

[Annas]

Thank you Roger. We are now weighing up going with an overlay board which is fairly low profile but of course not ideal, but better insulation. Are you going with JK ? - they look really good and have done some major projects inc museums and listed houses. I am very impressed with the cost too. Still torn. I know of someone local who had it done in concrete and is very pleased with it, so I think its certainly an option

[Annas]

Thank you Roger. We are now weighing up going with an overlay board which is fairly low profile but of course not ideal, but better insulation. Are you going with JK ? - they look really good and have done some major projects inc museums and listed houses. I am very impressed with the cost too. Still torn. I know of someone local who had it done in concrete and is very pleased with it, so I think its certainly an option.

And just to say its oil Joth- we live in a rural area. 

 

 

[Iceverge]

I was in a new house today with UFH in a slab above 200mm insulation. 

 

The house was a pleasant temp but underfoot the floor felt exactly the same as our house with 200mm insulation and no UFH. Not warm, not cold.

 

UFH with hot floors are generally a symptom of a badly set up system or a high heat loss house. 

 

The exception to this is electric UFH for bathrooms which is generally only for short bursts anyway just to heat your toes. 

 

 

[Roger440]

31 minutes ago, Annas said:

Thank you Roger. We are now weighing up going with an overlay board which is fairly low profile but of course not ideal, but better insulation. Are you going with JK ? - they look really good and have done some major projects inc museums and listed houses. I am very impressed with the cost too. Still torn. I know of someone local who had it done in concrete and is very pleased with it, so I think its certainly an option

 

Ill be doing it myself. You can hire the slot grinding machine, so straight forward enough, if tedious.

 

Ive looked at an overlay, but given id be doing the whole ground floor, it causes to many issues with doors, thresholds and the stairs, so ive discounted it. 

 

My house is 1800's solid wall with no DPC, so im not overly concerned about "warming" the wall as it will help push the moisture outwards, but im gussing yours is rather more conventional?

 

Im not convinced it will need to run at an overly high temp, but clearly it will be a slow to respond heating system. The one i did in my last house was semi insulated with foamed glass, but pipes right at the bottom of the slab. It worked really well and ran at 35 degrees.

[Onoff]

25mm? You'll be heating worms.

 

@Jeremy Harris on here had 300mm of eps under his floor slab. He calculated I think it was 8% of his total heat loss was through his floor with that much insulation. That's always stuck with me. 

 

If you're not fussed about cost it'll still feel nice underfoot, whatever. 

[Annas]

I didnt know you could rent the machine. It is conventional and dpc so would be good to know how would UFH potentially impact that? We'll be knocking down walls and will have new wood work and doors in any case - only issue, if we go with overlay, is shallow stair step! May look a bit odd.