Which underfloor heating system?

[teddyswift]

We are having an extension built, and at the same time recasting our double garage as a "family room". These two, together with the existing kitchen, will be floored in Karndean (yeah, I know, very expensive, but what can you do? I'm planning to buy it on-line reduced and lay it myself.)

So, my question is underfloor heating - is it worth it, and if so, are there any makes or systems that stand out? I'm not looking for bargain basement, but I am looking for reasonable value for money.

Thanks

Ted.

[Grunff]

I'll take this opportunity, if I may, to ask - what is the attraction? Why not some other similarly priced material, such as porcelain, marble, slate, hardwood? Why plastic, at that price?

Your choice is between wet and electric.

A wet system will be fed from your main central heating, via mixer valves. It is more work to install, will cost more initially, but is cheaper to run if you have oil or gas as your main heating fuel.

An electric system is easier to install, and quite a bit cheaper, but will cost more to run.

Your first decision will be to choose between the two.

Is it worth it? I think so, especially if you have tiles/slates over it.

[teddyswift]

I live not far from Karndean HQ and we went to visit. The whole place is floored in the stuff, and it looks really, really good. Of the options you suggest, if they really are in the same price bracket, then I've no idea why we're going the Karndean route.

Actually, I do know. It's called "option paralysis" - or at least that's what I call it. The relief that one feels when one makes a real decision in the face of endless choice is almost as good as .... In truth, Karndean is hardwearing, easy to clean, easy to maintain, soft underfoot and attractive.

It will be a wet system. So I guess my question is - is there much/ any difference between suppliers of these systems? In fact, is there a "supplier" per se, given that it's just a system of pipes and mixer valves.

Anyway thanks for the help so far.

Ted.

[Grunff]

For reference, here are rough prices:

Slates: from £20/sqm Porcelain (not ceramic) tiles: from £20/sqm Hardwood: from £20/sqm Marble tiles: from £30/sqm

That's fair enough, I'm not trying to change your mind, I just wondered.

You want to use decent quality valves, but otherwise as you say the system is made up of a bunch of components usually rom different manufacturers.

[The Natural Philosopher]

Well I got all my stuff from Polyplumb. Its as good as any..I DO like the manifold with the little flow gauges, and the modular installation tho.

I think the whole experience can be summed up with a few salient points.

1/. You can reliably expect no more than 50watts/sq meter. That means that its not suitable for poorly insulated houses. 2/. Efficiency of the actual 'radiator' - the floor - is critically dependent on the ratio of the insulation below, to the inadvertent insulation above. That is, if you want rugs carpets and furniture on a wooden floor, you had better be prepared for a LOT of insulation underneath, and pretty hot floor temperatures e.g. under the sofa! Thats why you need a temperature regulator to prevent the floor getting hot enough to crack! 3/. The screeded floor represents a HUGE mass. there is at least a three hour lag to getting anywhere near a 'warm room' and if your output is marginal, it can take far longer. 4/. If you have an auxiliary pump, you will probably need a relay to control the boiler. 5/. Because of the time lags, careful thermostat siting, possible subzoning and a 3 channel controller are almost mandatory. Or one of those clever predictive thermostats and no timer at all. In deepest winter running 24x7 seems to result in no more boiler activity than timing.

Having said that, the final result is excellent. We are more comfortable with warm feet at lower room temperatures than with conventional rads.

[teddyswift]

Thanks for the replies TNP and Grunff.

My further researched suggest that carpet is a no-no, which would be somewhat de trop on top of a Karndean floor. However, we do have a lot of rugs (of the Turkish variety) - will these affect things much? Someone elsewhere suggested that carpet/rug be no more than 1.5 TOG - how do you determine the TOG value of a Turkish rug?

Ted.

[The Natural Philosopher]

We've got rugs all over the (kahrs) floor, yes they make a difference,. no its not that serious.

[teddyswift]

I called Karndean and asked them about the preferred substrate for the floor. The girl in technical services told me that I would need to lay a reinforced screed of a minimum of 67mm.

So, I talked to a friend who had UFH and he said he'd never heard of

67mm - he had used 75mm for insulation, and 75mm for screen. So I called Karndean again.

(Me) "This 67mm reinforced screed - are you sure about that?"

(Same girl) "I'll just consult my colleague ... yes, that's right."

(Me) "It's just that 67mm is such a weird value - most people I've talked to have mentioned 75mm"

(Girl) "No, not 67mm, 627mm!"

(Me) "Six hundred and twenty seven millimetres? Are you having a laugh?"

(Girl) "No, 6 to 7 mm"

(Me) "You mean between 6 and 7 mm?"

(Girl) "Yes"

(Me) "Then why didn't you say so"

Ted.