Foil behind radiators

Andy Burns snipped-for-privacy@andyburns.uk wrote in news: snipped-for-privacy@mid.individual.net:

Thank you, I'm usually good at spotting those :-)

I was going to give a tinyurl but the f'ckrs converted it to an affiliate link even in preview mode (they used to do that only for direct tinyurls).

alan_m snipped-for-privacy@admac.myzen.co.uk> wrote in news: snipped-for-privacy@mid.individual.net:

Well there is aerogel which is best by far but stupidly expensive (don't even look).

Thinnest PIR I've found is 20mm Celotex (around 15quid a 2400x1200 sheet) if you can accommodate that but it wont be available everywhere and online places will kill you on delivery.

The specific superfoil radiator sheets mentioned sound like a reasonable starting point and reducing your flow temp will reduce that radiation transfer loss further. I usually modulate my flow temp manually depending on how cold the weather is, no point in banging out huge amounts of heat in corner seasons.

No, insulation is insulation. If what's behind it is insulation then its overall impact is less. So less point in fitting.

Even the Superfoil stuff is only (IIRC) 6mm. I just used that and one thickness of standard foam backed (about 3mm) I was given when the LEAP people (a govt scheme - think it's finished now) came round.

It does, but not significantly. The temperature of the cork will be within a fraction of a degree of the wall surface behind it.

I think it's more the fact that the material is less conductive, so less likely to allow condensation to form.

The moisture you had will still be there, all other things being equal. It'll either condense somewhere else, or remain in the air.

Yes, I was given a roll of it. It relies far more on an air gap than the material itself - so it needs to be mounted on battens. 'According to the manufacturer', if a 38mm air gap is used each side it's equivalent to 70mm PIR

- or at least the stuff I've got is, they claim. So overall about 80mm. And a fair bit cheaper, and looks nicer to fit.

Might as well try it as I've got a 10m roll of the stuff. But I'd agree, it seems rather unlikely.

Ah sorry, different things, this is what I've got:

RJH snipped-for-privacy@gmx.com wrote in news:10ar5uc$298mg$ snipped-for-privacy@dont-email.me:

My view was that something is better then nothing and figured 6mm of (glorified) bubblewrap would likely be better than 3mm of (non-PIR) foam.

RJH snipped-for-privacy@gmx.com wrote in news:10ar6m8$29dud$ snipped-for-privacy@dont-email.me:

It is complete snake oil and relies on those air gaps front and rear being entirely air change free (beyond draughtproof) so completely unachievable in real life. BS/EN hot box official testing has completely rubbished their claims. In short, bin it and buy some PIR.

Well, yes, not hermetically sealed. But sealed to the point that there'd be very few air changes, especially if installed internally.

Do you have a link - seaches just seem to bounce back to the Superfoil site. And one 'exercise caution' LA notice in 2013.

I am wondering.

RJH snipped-for-privacy@gmx.com wrote in news:10arc3t$2auv8$ snipped-for-privacy@dont-email.me:

Nah, I did follow the story when it came to the fore long ago but not since I was convinced of its oiliness. I now view it simply as a matter of common sense, PIR works by having microbubbles in closed cell foam thereby eliminating air circulation losses. There is no way that a bit of metalised bubblewrap or layered same, even in airtight boxes, can approach the verifiable performance of PIR.

In steady-state, it's very thin so only marginally improves the U-value of the wall. But I think what you mean is that you start boiling some water and the air temperature goes up as well as the humidity.

Supposing the wall was made of solid metal (a good conductor from the outside), the warm/damp air would hit the cold metal and condense. But if you put a poorly conducting cork layer on it, the surface of the layer can warm up quickly enough to be above the dew point so the moisture doesn't condense on the surface.

In steady-state, conductivity from the outside would still chill the surface, but when you're boiling a pan of pasta for 10 minutes the cork buys you enough time for it not to take place.

Result is that the wall remains condensation free when cooking, but may not if the air remains damp - if you have an extractor, a vent or an open window then the humidity will have time to exit that way rather than condense, which it would if the room was hermetically sealed and the moisture left in the air.

The same idea goes for 'thermal' paint, which is so thin it can't have much effect on the U-value.

Theo

Exactly my point?

It is not. You simply obviously have never used it not ever done te calculatins

Its because its "less conductive" that it insulates, and its because its "less conductive" that its inner surface can be massively warmer than its outer...up to 20 degrees in fact

Well duh

Of course its still there, It's just not condensing and causing mould, and the house is no longer icy.

The thermal conductivity of cork typically ranges from approximately

The thermal conductivity of brick varies, with typical values for common clay bricks ranging from 0.5 to 1.0 W/(m·K), though some sources cite a specific value around 0.8 W/mK.

So 50mm of brick is around the same as 3mm of cork.

In short for a real single brick outside wall with absolutely no insulation whatsoever, the heatloss is *halved* .

And that was borne out by experience of fitting it

Don't bin it; core R value is 1.63 with nominal thickness of 45mm, so similar to PIR. It's just not worth buying in most situations.

Except that corks is an exceptionally good insulator. It has a massive effect on the U value. So did the now banned polystyrene tiles.

A single brick house in a winter gale may have wall temperatures as low as 5°C. In fact that house once had a radiator freeze INSIDE the porch which was unheated at the time

Halving the heat loss kicks that up to around 10-12°C

The sad fact is that all those old Victorian semis with half brick wide walls would have been immensely improved with 3mm of cork or polystyrene, but the regulations say that if you are going to alter anything at all, it has to be to full modern regulations, which means at least 4" of insulation which really wont fit...,

The insulation works, it's the foil that is pretty useless.

I guess it holds the foam together, like celotex...

Going to ubakus.de, putting in:

Inside air 20C, 50% RH Cork 3mm Single brick 115mm Outside air -5C, 80% RH

gives a u-value of 2.859 and an interior surface of 6.7C

Turning off the cork and just having single brick gives a u-value of 3.451 and an interior surface of 4.7C.

It's better, but it's not an order of magnitude better.

If I go up to 10mm cork, it's U=2.042 and surface = 9.8C.

If I go to 10mm foil-coated PUR (I think that's the German for PIR) it's U=1.45 and surface 12.3C.

It's better than nothing, but you would be better to use PIR if you can. I suppose if you like cork as a decorative effect or for soundproofing then it could make sense.

You don't need to do that. If it's a 'renovation' yes, ie taking the roof off and building everything anew inside the walls. Or if you were building a new exterior wall. But if it's retrofit then you aren't bound by the modern regulations.

Theo

Something doesnt gybe there

Whast u values for brick?

It wasn't my house. I did what I could get away with

You sort of are. If its a 'material alteration'. And fitting insulation is exactly that. strictly

So a builder wont do it. As an individual you can get away with it by pretending it was always like that, guv