Carpet over UFH. is it special stuff?

[saveasteading]

We have a downstairs bedroom to carpet.

Suddenly the Carpet-right quote of £28/m2, laid, incl underlay, becomes £50/m2.

 

We do appreciate that an insulating layer over the heated screed isn't the cleverest thing.

There appears to be specialist underlay that is less insulating then the norm, at £9/m2.

Also special carpet, and the laying is now extra.

 

Any comments at all please?

 

There is also the flooring industry try-on of quoting for gripper /m rather than in total.

 

[JohnMo]

Our carpet underlay in the bedrooms is what looks like a perforated standard underlay (although we specified UFH underlay), we also used expensive wool carpet.  Both do a really good job of isolating to floor heat from the room, so UFH is pretty rubbish in the bedrooms, good job we like them cool.

[saveasteading]

I have done some research.

Basically underlay has tog of about 3.0, but the special stuff is 0.7, so much more heat comes through.

Avoid foam-backed carpet, or wool. 

Carpetrght have their own name for this special underlay and sell it at £13/m2. it is called Duralay elsewhere and the cheapest I have found is £9/m2.

Delivery to the Highlands is stupid extra money as often. (£70 for the last 50 miles from the notional barrier to transport). I think free with Amazon, much as I'd rather not use them.

[Temp]

+1 to the above.

 

Some carpet salesmen haven't a clue. I once asked for the TOG value of a carpet sample and the man went away to check and came back with some ridiculous number like 10 or 11 written on a post it note. Think that's more like a duvet. 

 

Others told me all their carpet was suitable for UFH - meaning it wouldn't be damaged by it, not that it would let the heat through.

 

Ideally keep the total TOG to below 2,5 and ideally 2.0. 

Ask to see the makers specification which sometimes states the TOG.

 

Beware: Some carpets are made in two versions. Foam or Hessian backed. Some shops have terms in their small print on the order form that allows them to choose which version they supply. You don't want to order hessian backed based on its low TOG and find that foam backed is delivered.

 

I recommend trying out samples of the underlay and carpet together in bare feet as some very low TOG combinations can feel a bit hard.

Edited February 24, 2023 by Temp

[Radian]

50 minutes ago, Temp said:

Beware: Some carpets are made in two versions. Foam or Hessian backed. Some shops have terms in their small print on the order form that allows them to choose which version they supply. You don't want to order hessian backed based on its low TOG and find that foam backed is delivered.

 

 

I've mentioned before that we've done something a little different. We've gone without underlay altogether and got the carpet fitters to stick a carpet direct to the floor. They use hessian backing for this kind of application. The carpet itself has a TOG rating of 2 so that's it. The effect is that you get a nice warm floor, softer than laminate or tile (and sound deadening) but without a spongey feeling. Suits us fine.

[SteamyTea]

A TOG is equal to 0.1 m².K/W.

To get to the nicer to understand U-Value, inverse it.

U = 1/R_SI

 

 

 

[Kelvin]

16 hours ago, Radian said:

 

I've mentioned before that we've done something a little different. We've gone without underlay altogether and got the carpet fitters to stick a carpet direct to the floor. They use hessian backing for this kind of application. The carpet itself has a TOG rating of 2 so that's it. The effect is that you get a nice warm floor, softer than laminate or tile (and sound deadening) but without a spongey feeling. Suits us fine.

Good tip. My Hi-Fi/music room will be carpeted over UFH in Gunn Modern tartan that’s hessian backed so shall keep that in mind. I’m prioritising acoustic performance over heating performance for this room albeit the amps will help heat the room up when in use. 

[Radian]

19 minutes ago, SteamyTea said:

A TOG is equal to 0.1 m².K/W.

To get to the nicer to understand U-Value, inverse it.

U = 1/R_SI

 

 

 

 

I had to look up the definition of TOG and google offered up this which I thought was quite handy:

 

 

 

[SteamyTea]

33 minutes ago, Radian said:

had to look up the definition of TOG

Did you see the bit that it was a bunch of Manchurian academics that names it after the slang term for clothing.

[puntloos]

So reviving this topic somewhat. My plan:

 

- Passivhaus + ASHP

- Downstairs tile + UFH. 

- Upstairs twist carpet. Tog of carpet (1.7) and underlay (0.8) so exactly 2.5 (below this: concrete block and beam)

 

Will this be ok for a bedroom assuming outside is not less than -5C ? (in cold emergencies there are other ways to heat)

 

Some thoughts:

- ASHP doesn't produce super hot water for UFH so it might somewhat struggle

- But "trapping" heat typically doesn't mean it's wasted, just slower to percolate into the room?

- Or will I only heat my concrete 1st floor flooring? 

- I heard (citation needed) that many passivhaus places don't even have any heating on 1st floor so wouldn't I be fine either way?

 

Thoughts? What's the lowest-tog twist ("long-ish, luxury foot feel") carpet you've found? 

 

[puntloos]

Update: Ergh, so far I can't find a single carpet retailer that allows me to filter by tog rating. 

Best I found so far: 1.2 tog, 12mm high.

https://www.flooringhut.co.uk/cormar-carpets/cormar-primo-choice-elite/cormar-carpet-co-primo-choice-elite-zinc

[JohnMo]

The biggest issue is a passivhaus will have really low flow temps for UFH. Carpets just act as an insulating blanket. Our house isn't passivhaus standard but is well insulated. Our UFH flow temp is low, floor surface temperature is 1 to 2 degrees above the room temperature. We have carpet in the bedrooms and the UFH is just rubbish.

[saveasteading]

8 hours ago, puntloos said:

carpet retailer that allows me to filter by tog rating. 

 

Even then , I have seen small print that allows them to change the backing from woven (and open) to a foam sheet.

[Ben Weston]

Reviving this again: we have wet UFH upstairs and had planned to put carpets down but the more I read into it the more I think it's not a great idea. I like warm, squidgy carpets in bedrooms but if it stops them getting nice and warm in the depths of winter, I'm not so keen!

 

I presume an LVT wood floor would be far better for heat transfer with the correct UFH underlay? 

[Conor]

We've normal carpets with the special underlay and it works fine. You don't need that much heat output upstairs anyway. 

[saveasteading]

2 hours ago, Conor said:

We've normal carpets

I'd think that normal, foam backed carpet will insulate the floor more than normal hessian backed carpet.

[dpmiller]

do they use foam any more? Isn't it generally a synthetic felt-like layer now?

[saveasteading]

3 hours ago, dpmiller said:

do they use foam any more

Maybe not foam, but some backings look much more permeable than others.

Trying to blow through it might look strange at Tapi.

[Conor]

11 hours ago, saveasteading said:

I'd think that normal, foam backed carpet will insulate the floor more than normal hessian backed carpet.

 

4 hours ago, dpmiller said:

do they use foam any more? Isn't it generally a synthetic felt-like layer now?

We got our from Martin Phillips carpet, all the carpet they sell is low tog and suitable for UFH. It's not overly thin anyway.

[bassanclan]

This may be helpful to someone:

https://www.cormarcarpets.co.uk/tog-values/

[Redoctober]

16 hours ago, Conor said:

We've normal carpets with the special underlay and it works fine. You don't need that much heat output upstairs anyway. 

 

Plus 1 to this. 

[puntloos]

We have 0.8 tog underlay, and there is a huge range of "normal" but I would still strongly suggest you get as low tog as you can find, within reason. Point being that a strong insulating carpet will direct the heat downward, which means that while it might not be 'lost' it will end up in a place you don't need it. 

[Bozza]

As per a previous post by @Radian an option is to not put an underlay down and just use a low tog carpet.  Obviously not as spongy but certainly softer than a hard surface.   Another compromise option is to put down LVT or whichever hard surface,  then get rugs made from carpet with bound edges for areas you’re likely to be walking on.  So only part of the floor is covered.

 

A carpet without an underlay on UFH will feel softerwhen warm.  It kind of tricks the mind, like floor tiles alway feel softer when warm. 
 

[Temp]

Just a heads up... I went to a few carpet shops and about half told me that ALL their carpet and underlay was suitable for UFH. What they mean is that the carpet won't be damaged by your UFH not that it will let any heat through.

 

The manufacturers data normally has the TOG info in it but many shops seem to throw the data away. You need to be sure anything they tell you applies to the carpet you are buying. Match up the part numbers or order codes with the same number in the manufacturers data. I asked one sales rep about the TOG value and she went to investigate, came back with TOG=10 on a post-it note claiming its fine for UFH. 

 

Some carpet is made in two versions, one with a hessian back and one rubber. The hessian backed has lower/better TOG. Beware that the small print on the order form may allow the shop to supply either version. If you want/need one or the other make sure that's noted on the order. 

 

Some low TOG underlay is a bit thin. I recommend trying a sample of the exact underlay and carpet combination under bare feet to confirm it's the feel you want and not too hard.

 

It's worth finding a sales rep that knows about UFH.

 

 

Edited November 26, 2023 by Temp

[puntloos]

Getting back to this in a bit of a different slant - we would like to have a rug in our livingroom, but indeed the 'tog' struggle is real. Even more than with carpets, very few 'rug makers' mention it at all. A lot of websites claim that natural materials are lower tog, but I don't really see why this would be. It might be a worthwhile rule of thumb if people don't know, but in the end you probably want the real measurement rather than a handwave. 

 

Secondly, anyone have any experience with converting a carpet into a rug? Are there local tailors or carpet teams that are able to do this?