Best underfloor heating system

[leenowell]

Hi all,

I am refitting a bathroom and am looking to install underfloor heating. Ide ally, I would go for water system because I can fit it myself and I have a spare zone on an existing manifold which heats downstairs.

The bathroom is upstairs with a joist floor and the finished floor would be tiles.

The systems I have seen after a great deal searching all seem to rely on me putting wooden boards on top of the system and then tile on top. Given the good insulation properties of wood, and it doesn't retain much heat (unlik e the screed downstairs) I am concerned this would not work very well or be very inefficient.

Ideally I would have a system which is a bit like the spreader plates but a re themselves load bearing so you could tile on top without the boards.

Anyone have any experience on either how good the systems I found are in pr actice and whether my 'invented' system actually exists?

The other option I guess would be to go for electric on top of the ply but I assume I will need a qualified electrian to connect it up?

Thanks in advance

Lee.

[0345.86.86.888]

Hi Lee, About 6 or 7 years ago I did the whole of our upstairs area (4 zones) I looked at the spreader plate method and was concerned (wrightly or wrongly) about possible expansion/contraction noises so went for a thin (15mm) "dry" screed.

The layers are built up with batons half way up the joists which support ply (6mm I think) on which there is celotex, can't remember the thickness but I think I had to go down slightly (perhaps 50 or 55mm) to give enough clearance for 15mm to joist top. Pipe is clipped to cellotex and "biscuit screed" on top.

Green Chipboard floor 18mm over everything and on top of that we have Kahrs (15mm) engineered wood flooring.

Works perfectly. Heat coming through is simply a matter of insulation below V insulation properties of the wood above. I also stuffed the voud underneath the cellotex with mineral wool more for sound reduction to bedrooms below but no doubt also helps "push" heat upwards.

Just looking at doing our new extension now which is concrete slab on insulation and will most likely go with something like

possible with a multi-foil layer between the slab and boards to improve response times.

Maximum output temp of our boiler is 55 degrees with weather compensation so when outdoor temp is higher than 5 degrees the flow temp modulated down. 13 degrees outside sees around 30 to 35 degrees water flow which just takes the edge off the floor and still pushes the room temp up to switch off room 'stats if required. Hope that helps. Prete

[Brian-Gaff]

I only encountered this once in a building and did not like it as some parts of the floor were very hot to bare feet, whilst others were cold. I guess its different. I wonder if its efficient or just a novelty. I'd have thought by now some clever chappie might have developed tiles with inbuilt heating. :-)

Brian

[rick]

Be warned you can't just tap into heating system .... UFH requires lower temp than rads .. you need to have a blending valve to set a max temperature. Plus it should be and ferrous free to avoid problems.

When I researched this ... I opted for NuHeat UFH ... and I put a whole house system in .... very pleased with it. Its a small bore pex pipe install.

[www.GymRatZ.co.uk]

"myself and I have a spare zone on an existing manifold which heats downstairs."

;¬)

You /can/ actually tap into an existing CH system. That's what the blending vale does, it feeds cooler return water back to blend with the incoming water or indeed shuts off incoming hot water completely if the temp is too high and keeps circulating the water through the UFH pipes until it needs to let more "hot" water into the blend.

Obviously this leaves no room for error should the blending valve or it's thermostat decide to stay open which is where the peace of mind comes from with having boiler only putting out UFH temps,

I have a 4 zone UFH doing the upstairs and a regular radiator circuit doing the bedrooms.

Needless to say, I have the boiler set with a max. output of 55 degrees but having bedrooms half underground meant even without heating I didn't ever see the temp drop below 12 or 13 degrees so UFH water temp is more than ample for bedrooms without having grossly over-sized radiators in our house at least and, I shouldn't wonder, in most houses with "up to spec" insulation, glazing etc.

Nu-Heat started off supplying some very dodgy rubber pipes made by a Monsantano company all of which broke down and leaked within a few short years. I wasn't aware of this when I did ours but it's done in PEX fast-flo pipe. Only issues I've had are having to replace all the individual zone control heads where either they simply failed or the plastic cracked and couldn't hold the valve open.

Oh, and the zone flow indicators on the manifold of which 2 have now seized but that's not a big issue really.

[The Natural Philosopher]

plus due to the enormous length of time it takes to get screed warm, you probably want it on a separate circuit with its own pump and timer

Polyplumb. Also very pleased.

[Andrew Gabriel]

I've done a couple of bathrooms across the family now. I have simply taken the standard radiator feeds (without blending valves) and fed it into a couple of 10mm copper circuits which snake up and down between the floor joists, supported an inch or two below the joist tops by some small cross timbers, and spray painted on the top to aid radiation of heat onto the bottom of the floor boards (or ply for tiles in both these cases). I used loose fitting plastic P clips to keep the pipes in place, but allow lengthwise expansion/contraction without stress.

I was not certain how effectively they would pass heat into the bathrooms, so I included a TRV in both cases. Raising the pipework into the room for the TRV also gives you the opportunity to fit an air bleed valve. In the second case, the outlet from the UFH feeds the inlet of the towel rail, allowing the TRV to be fitted there and using the towel rail's air bleed. Keep the pipework horizontal so it can't get air trapped in the underfloor sections, and it will be pushed towards your bleeding point by the pump.

In both cases I avoided heating directly under the toilet pan - didn't seem like a good idea to leave that with heated water in the trap, but the pipework does cover where your feet are when using the pan. Watch out for any cabling, particularly anything which might be running near it's current capacity which will be unsuitable for running in a heated space. Lighting cable in a house is not normally a problem (it's normally fused at a fraction of its current carrying capacity), but make sure it's below and away from the heating pipework.

Dirt cheap solution costing little more than a coil of 10mm copper tube, TRV, and some fittings.

If you already have a heating circuit which is temperature controlled for direct contact UFH, then you should probably use that instead, but if your heating doesn't, then the scheme above seems to work fine.