This weekends project - install underfloor heating. Sanity checks needed :-)

[Mark Gillespie]

This weekends project, is to fit underfloor heating into my conservatory= =

project. I bought a kit from a UK supplier (eco-hometech), and it seems= =

to have everything I need.

The conservatory area is 18.6sqM and the supplier recommened 3 pipe =

sections from the manifold/pump. I have arranged my pipes in a =

counterflow pattern, with 100mm centres, and achieved pipe run lengths o= f =

62m, 52m, and 55m

Does this pipe layout seem OK? (excuse the dodgy grid, as it seems Googl= e =

Sketchup is incapable of grids)

are a couple of small runs where the hots run next to each other o= n =

adacent sections, which are hard to avoid. I am asuming this will not b= e =

a big deal.

I really only have one question.

I am clipping the pipes down directly onto celotex foil backed insulatio= n. =

I have taped the joins between the foil boards with foil tape. The kit = I =

have, has edge insulation, and the insulation handbook says the followin= g:

"IMPORTANT: if you are going to use a liquid screed you need to use an =

expansion strip with a thin polythene strip attached to it. The polythe= ne =

strip must be taped to the membrane that has been laid on top of the =

insualtion with specialist floor screed tape to ensure a watertight seal= ".

Now all that seem quite scary and implies it's important... I will be =

using a sand/cement screed, but unsure if this is classed as a "liquid =

screed".

So my question is, do I need to do any additional taping/waterproofing =

with a sand/cement screed? Or can I just pin the pipes down to the =

celotex, and lay the insulation strip around the permiter. Or do I need = to =

do special stuff.

I think that's all for the moment. Hopefully I have everything prepared= , =

and I can get most of the kit down this weekend (I might not get the =

manifold in, as it's going under the floor in the living room, and it =

means lifting floors..)

Any other tips and knowledgable folks here can help with???

Many thanks.

[TheOldFellow]

It's important that the expansion gap round the outside of the slab is maintained. With a dry-ish screed the mix wont run under the insulation band, but a slurry will.

If you don't maintain the expansion gap on a 18m2 slab, it will crack due to expansion, and then the pipes may abrade as the pieces move.

I would just use, say gaffer-tape, to seal the edge insulation to the celotex, that way your screed can't get into the gap. It doesn't matter if the seal degrades later, the slab will be set.

The other important, nay VITAL, thing is to let the slab dry AND CURE well before putting the heat into the pipes. Say 6-8 weeks. I also pressurise the pipes with water to 6 bar while the screen is laid, and then for a couple of days - to make sure the pipes don't get kinked or crushed.

R.

[Black Shuck]

Many thanks for that! How do you pressurise the system to 6 bar, without running it? Do I need to buy special kit to do this? I was thinking of fashioning a valve into a bit of copper pipe and soldering it in, so I can pump it up to 6 bar of air, with a foot pump. Is there a better way?

[dom]

Wouldn't it be easier to keep a dry test gauge on?

with a car foot pump)

[TheOldFellow]

Well, I have a Rothenberger test-pump that fills and pressurises with water, then it's already full when you connect it up :) I guess 6 bar is 6 bar, though, so an dry test would seem to me to be OK.

Remember I'm a DIYer, not a plumber, though.

R.

[Tournifreak]

I used the Eco-hometec wet UFH system about 2 yrs ago - and it's still working!

Unless they've changed their pipework, I'd say some of the angles in your layout are unachievable. The pipe they used to supply (16mm IIRC) is really quite stiff, and I don't think you'll get a radius any less than 50cm.You *really* don't want to put a kink in it. Some of the acute angles you have in your layout, are too sharp, I think.

Don't worry about tape etc. The clips will hold the pipe in place just fine. And the screed will hold the edge insulation in place too. Just make sure whoever does the screed for you doesn't remove it!

Alos, I'd plan to leave a bit of pipe left over. One of the most stressful times in my project was when I was laying the pipework the day before the guys were coming to lay the screed. Somehow I was 5m short. Had to get some more sent by courier, which inevitably was late. They started laying the screed, and the extra pipe and coupler arrived just as they got to the bit I was working on.

Everyone says you should pressurise the system. I must admit, I filled it, but didn't pressurise it. I really didn't see the point. The pipe is *so* tough. You can stand on it, no problem. And 4 inches of concrete just ain't that heavy. As you say, pressurising it is a pain.

when it's done though...lovely! :-)

Jon.

[Andrew Gabriel]

I did that using a dry pressure test kit on all the sections of my heating system before I let any water in.

72940 if that link doesn't work)

[The Natural Philosopher]

No. What they are saying is 'take precautions to prevent any screed getting behind the expansion strip'

[The Natural Philosopher]

Far more dangerous. Air is compressible and contains energy when compressed. Water is not and doesn't, largely.

I hired my gauge and hydraulic pump for a fiver or so for the day it took to lay the screed..leave pressure on about 24 hrs.

Letting screed dry is a good idea, but its not necessary that its DRY, its necessary that its fully set. 6-8 weeks is 'proper' but I think you would get away with one in practice.

[The Natural Philosopher]

In your cae you should have, simply because it sounds like you committed the cardinal sin of joining a pipe under the floor.

You should do your runs to the manifold carefully as a complete run of pipe. If that means you have a load of 20m or so lengths left over, so be it.

Pressurising may not be necessary, but if you have - say - a pinhole leak in a pipe, its a small price to pay as against having to rip up all the screed after its gone down..

[Stevie B]

Yep, I anticipate this, I was being lazy when I drew it out. The handbook says 90cm radius I recall. I just means my runs are slightly shorter than I planned. But I will work around this as I lay it.

Screeder is not booked yet, I am going to wait until it's down, and I can afford it!!! :-)

I might invest in one of the screwfix jobbies, and then sell it on afterwards, or have a poke around on ebay tonight....

PS. I am posting from my Google Groups account, so I don't know what my display name is, but I have already noticed by laptop and desktpp PC have different usenet names// Black Shuck =3D=3D Mark Gillespie =3D=3D Whatever this comes out as!!!

Thanks to all for the advice. Wish me luck :-) I;m going in....

[TheOldFellow]

I'm not a concrete chemist, but my father (88) is. He says that the full strength of the screed won't be developed until significant crystallisation has taken place, and that takes some weeks. In fact concrete keeps getting stronger for centuries!

OK, if you are only going to walk on the slab, or maybe spend a week or so laying tile or stone or laminate, a week will be OK. But not to put point-loads on it, chair legs for instance. It really depends on what you plan to do next.

R.

[Tournifreak]

Thinking back, I did do a quick leak test - pressurised that run for a few minutes. The join I used was quite impressive. Not like anything I've seen before. A sort of compression joint on steroids.

You're right - ideally I should have replaced the whole run. But the screeders had already started laying screed over the other side of the room! You live and learn I guess. Always buy a good length more pipe than you calculate you'll need.

Jon.

[The Medway Handyman]

Someone told me that the reason the WW2 Pill Boxes that are scattered around haven't been demolished, is that the 50 year old concrete is so tough & they would be difficult to knock down.

[Roger]

The message from "The Medway Handyman" contains these words:

I think it is a matter of cost. Reinforced concrete that may be several feet thick takes time and a good deal of effort. When I was a child back in the 50s there was a corner site on the sea front that was partly occupied by a large concrete pill box where we used to play. A prime site for housing so eventually the pill box was demolished.

A rather more questionable clean-up operation was the removal of a series of concrete cube tank traps that used to line one side of a school playing field. The concrete pill box across the way is still there but with its entrance blocked up as are a few more tank traps that weren't within the school perimeter.

Just in case anyone wants to know the locations the first pill box was located on the corner of Beach Road and Lower Marine Parade, Dovercourt, Essex and the demolished tank traps along the boundary between what is now The Harwich School and Half Acre Lane. The second pill box and the remaining tank traps are close to the junction between Half Acre Lane and Squat Lane.

Nearby on the former Allfields allotments someone had a brick built pill box in their garden but I cna't now locate it on Google Earth. Given that my last sighting of this must have been while walking my dog some

10 years ago it could have since been demolished or it could be conpletely shaded by trees.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Mark Gillespie" saying something like:

There's on thing I would change and that's the rightmost loop. Reverse it, so the hot goes along the outside wall first and then continues inwards. The other two loops are fine that way.

[Andy Champ]

I'm very puzzled by this, and since none of the plumbers here have complained, it must be me.

The first thing all of the circuits do is to run a hot feed next to a cold return, and for a good long length.

If I was designing a system to transfer heat between two fluids, that's exactly what I'd do. It looks like a great way of transferring heat from the incoming hot to the outgoing cold. As this is obviously not the intent of the system, why doesn't this happen?

Andy