Electric under floor heating (UFH)

Anybody know where I cah find a good wet vs dry (water vs electrical) under floor heating comparison. Most webistes I've found are either sparky's or plumbers and so only fit one type. We've not even dug the footings yet so I am still free to choose which sort but I don't know the drawbacks or benefits of either type.
Any clues?
I would guess electrical Pros : easy to fit, makes less difference to floor height, easy to control on a timer, can be run independantly from whole house heating meaning you can warm the conservatory floor without baking every one else in the house Cons : more expensive to run
water Pros : cheaper to run Cons : more preparation eeded for the floor, more expensive to install
Any comments? ChrisJ
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ChrisJ wrote:

Water is not that expensive from scratch.
The cost of the pipe is not much worse than radiators would be...that leaves the manifold, auxiliary pump, motorized valve and probably a relay. A few hundred only.
You can run it as independently as you care to fit timers switches and zone valves.
If you are laying screed floors, its no worse than the screed anyway. Upstairs of course it does get more expensive as you need extra insulation and care with the joists.
With energy costs as they are, I;d go water...until and unless nuclear powered electricity comes down below fossil fuel costs - when we will all have electric boilers anyway retrofitted :-)

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ChrisJ wrote:

To add to what you and NP already said, I think it depends a lot of floor area. If your extension is a small-ish conservatory I think you'd be best off with electric. If it's a whole house, definately go for a wet system. The UFH pipe is cheap, laying it (downstairs) is easy, makes no cost difference to the screed (although you may need some sort of additive - check with whoever is laying it). With a wet system you need a pump, zone valve, pipework to existing system, mixer valve etc. So the cost per m2 is quite large on a small area. But for a large area, the cost per m2 would be pretty comparable to a dry system I would think. And the running cost for wet will be much less.
Don't skimp on insulation under the screed. I used 100mm Celotex. Don't use Jablite!
Google this forum for my review of the eco-hometec (wet) UFH system.
Regards,
Jon.
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Tournifreak wrote:

I wish I had. I used 50mm polystyrene (blue) and its not really enough, although it meets regulations.

My system was polyplumb:- www.polyplumb.co.uk
Do note that I forbore the use of the extremely expensive trays to lay the pipes on.
4 hours of my time, and a computer drawn layout were enough to enable me to tie wrap the pipes to a reinforcing mesh laid under the screed...
Then pressure up and screed away chaps!
It was alarmingly simple.
Wish I had done it upstairs as well..

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The Natural Philosopher wrote:

My big problem is laying the floor. The house is 9m front to back and there is at least 8m of front garden and pavement. There is no access to the back of the house where the conservatory is going other than down a flight of thirteen steps as the house is on a hill. This is not ideal for carrying either ballast to put down for a solid floor or concrete beenms for a beam and block floor.
Equally its not great for removing the spoil from the footings. My calcs so far: 4x3.5m coservatory gives 11m of footings. At 1m deep by .5m wide gives 5.5m^3 of spoil. As the damp proot course is currently about 3 courses of stone above the current ground level I was going to suggest putting some of the spoil under the floor of the conservatory. 5.5m^3 of spoil over 14m^2 (3.5X4m) would be 40cm of soil which I think is possible (especially as some can be put in front of the conservatory to reduce the number of steps down from the doors.
So this gets rid of the spoil without carrying it up the steps but still leaves the problem of the construction of the floor. Assuming concrete beams are out due to the weight and awkwardness of craning them (and the screeds) into the back garden what other options are available?
I've read that you can put wet UFH in a wooden suspended floor by laying the joists, covering with a fabric draping into the gaps and filling with insulation, fitting "trays" between the joists and laying the pipes on these "trays". We intend to have a ceramic tiled floor so the kids can run in and out of the garden without messing any carpet. What are the disadvantages of wet UFH in this type of floor? What else can be done to get round these disadvantages? (bearing in mind thre problems of access)
Chris
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ChrisJ wrote:

Its not so bad on the block and beams.
You can slide the beams down - they will be just about manageable by one person, but two is safer and easier.
I would say your greater problem will be getting sand and cement down there whatever you do.
The foundations have to be laid...that means tons of stuff going down.
What you need is to hire a mini digger that will go down the steps, and build an access ramp of earth or hardcore over those steps, so that you can at least drive it up and down. or run a barrow down.
Trust me on this: Make a ramp even if it means covering the steps. Maye sheets of ply backed up by earth? whatever.

Well they are not. Block and beam is useable, as is anything else.
It sounds like you are building at a lower level than the rest of the house..try and match the damp courses if you can.
As I said, first sort out access and transport. Even a wheel barrow will take a 1/6th ton down fairly easily ..and nothing has to come up.
and even if it does, two people and a rope can haul 1/6th ton on a barrow up a steep slope...its amazing how much material you can move on a barrow if you are fit enough.
I do have to say right here and now that UFH may not be adequate for a fully glazed conservatory in winter..unless you arrange extra insulation like curtains. Its very hard to get overall U values to the right levels even with the best glazing technology, and almost impossible with a fully glazed roof.
However, assuming that you go this route, I would do the following. Since you are likely to have problems compressing the spoil enough to make a stable floor surface..I'd definitely go block and beam.
Start by digging sensible foundations - really sensible ones - and build the wall up to damp. Since you are on a slope, and intending to shove spoil behind the wall, you need to be MOST careful about that wall.
I would build it out of concrete blocks on the inside, every one with a tie, and use a concrete block outer below finished ground level, and tie the inner and outer together with ties, fill the gap with mortar and punch a few holes in it to allow drainage - you don't want any water that seeps inside the foundations to stay there.
In addition if you can uses a third later of blocks on the outside under finished ground as a buttress. Use ties EVERYWHERE.
Once you have this wall built load up the inside face with gravel. This will help equalize loads on it if the inside shifts, and keep the local water table down ..all good stuff.
Now chuck in the spoil up to about 8" below the floor level. Its a good idea to put vents in the walls above this..just below the floor level..
And excess spoil you can use in the garden to terrace - scrape off the topsoil with a digger, slap the spoil down and put the topsoil back, I did this with a retaining wall to build p the area immediately behind the house..so I have a split level garden with a high part bounded by a wall with steps going down to the lower part.
Then lay your block and beam, blind it with sand and cement, and lay your DPM over the top, meeting up with the DPC in the wall.
Now continue the wall up to as high as you choose.
Lay in a shitload of insulation. 4" of polystyrene or 2" of celotex..and lay it up the walls as well. Put your UFH in in a metal mesh - ideally as close as possible - probably 100mm spacing as per the 'double spiral technique. Pressure up and screed to at least 3".

Honestly it is all possible, but I am no fan of suspended timber floors. Even a block and beam flexes..the timber will be worse and there is a serious danger of tiles cracking.
Plus ventilation and water sub floor needs far more careful management.
Bite the bullet and build some access. You will not regret it. Do NOT pretend to yourself or your family that the garden will survive. Be brutal, turn it into a building site, get the access sorted, and tidy it up afterwards. All plants need moving away to holding beds (or junked) and you will need area for storage of materials - cheap ply sheets are ideal for dumping stuff on.
Your plan should include all that, and a plan to restore the garden afterwards.
As long as you can arrange at the least a barrow wide ramp of no more than about 30 degree slope, you will be able to move materials with ease. You can get a small digger down that as well. And maybe a teeny dump truck.
Diggers are expensive to hire, so only do that when needed, but dump trucks are relatively cheap. Its almost worth having one more or less permanently.
You may also need to dig new soakaways for water run off..BCO will advise.

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Yes.
That depends. Sometimes wet heating can be installed without affecting floor height.

Actually, it is illegal to install wet underfloor conservatory heating (or radiators for that matter) that doesn't have independent control, so this is not an advantage of electric.

Massively so.
For a conservatory, I wouldn't dream of using electric underfloor. I would reserve electric underfloor systems for small bathrooms.
However, before installing even a wet system in a conservatory, consider the way you intend to use the room. Underfloor heating is ideal for situations where a constant temperature is required over long periods of time. If your conservatory will be used irregularly or for short periods (i.e. dining room), then a system that brings it up to temp quickly will be far more efficient. An ideal system for these would be a fan convector, such as a Myson Hi-line above the door.
Christian.
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Christian McArdle wrote:

That is an excellent point.
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