Adhoc underfloor heating

[Robin66]

I'm about to refit my kitchen, replacing a wooden floor with porcelain tiles. I've had what I think to be an ingenious idea and I'd like to run it by everyone. After laying and securing 18mm ply I plan to cut a 10mm (deep & wide) channel with my router across the floor in a wavy pattern and push in 8mm microbore coper tube available v cheaply on ebay. I can hook this up to some nearby central heating pipe, then cover with adhesive and lay tiles as usual and et voila I now have underfloor heating. It's quite a small kitchen with a floor area of ~4m^2, so the length of tube used would be ~10m.

Has anyone ever done this before? I can't find any examples on line. Some points that I've considered are:

• Thermal expansion of wood may cause tile cracks
  Uniformity of heat distribution will be quite poor
  Must allow tile adhesive to dry for a week or so before testing it out
  Floor will be weakened due to channel being cut

This doesn't need to throw out a lot of heat. I just want to make the tiles slightly less cold, and I'm happy that it'll only do so when my CH is on. As I said the floor area is small and well supported underneath so I'm not concerned about the ply weakening (mitigated due to the wavy pattern).

All ideas/thoughts appreciated

 

[Diyisfun]

How will you control flow & temp?

 

[Robin66]

The flow can be reduced if need be by an inline tap where I connect it to the CH out/return. The temp. won't be controlled beyond that of my house's central thermostat. At the moment my kitchen has no heating and is slightly colder than the rest of the house. The plan is to bring it more in line and warm the tiles a little

 

[muggles]

Sounds like a terrible idea. Buy yourself an electric UFH kit if it's only for a small area

 

[Dan Robinson]

You don't run ufh at the same temperature at the same temperature as radiators...


You need a blending valve and pump.

You also need to size the length of the loops to enable even heat distribution.

 

[Robin66]

My research found that UFH on timber floors has a water temp. ~55c. My rads are at 60c which isn't too far off, but yes I could put in a blender valve if need be. I don't see why I need a pump; the CH pressure should be fine for such a small area with 8mm bore pipe.

 

[Dan Robinson]

Crack on then

 

[Tipper]

You'll need heat spreader plates otherwise you won't feel much heat on your floor surface.

 

[Robin66]

Ah yes, spreader plates are a good idea. On ebay you can buy copper foil, 1mm thick, 50mm wide, for £2.50/m (Guitar pick-up foil). 4 metres of that would be plenty and would greatly increase the effective contact area between the warm pipe and the tile adhesive.

 

[Norcon]

At least fit a danfoss FJVR return temperature limiter. There about £45 quid including the sensor.
The wall mounted version around £75 quid.

 

[roguetrader]

Waste of good copper.
Electric floor warmer is the ideal thing for that sort of area.
What you propose won't work.

 

[Robin66]

Waste of good copper? I'm considering £40 outlay for tube and £10 for tape, so not a big waste. Why don't you think it'll work? I thought there may be good reasons why people don't do it hence the post, but I haven't heard any yet.

I've often noticed an accidental warm patch on timber and concrete floors just from the positioning of CH pipes, so based on that it shouldn't be too onerous to create a deliberate warm patch.

 

[Dan Robinson]

You've been told why, but you don't want to listen.

Frictional loss will be too high.
Temperatures will be inappropriate.

Also, floor structure might be unstable.


But you crack on fella. You're not the first to have a daft idea that just about works enough to feel vindicated.

 

[Robin66]

I'm listening but I've obv misunderstood. Can you tell me which temp is appropriate for UFH on a timber floor under porcelain tiles? My rads are currently set to 60c so I'm guessing your answer will be nowhere near that.

Floor structure might be unstable? I mentioned that in my orginal post but that would rule out underfloor heating on any suspended timber floors. But I've been told electric would be fine. Is electric heat different to wet heat? I have a phD in physics so you don't need to water the answer down for me

I'm still considering whether it's worth it because I've got limited time to fit the kitchen and can live without the heat source.

If I go ahead, worst case scenario the tiles crack as soon as I've turned it on and I've wasted a day and £60, and have to replace the cracked tiles.[/b]

 

[Stephen7]

Main problem you will have is heat migrating downwards due to lack of insulation. It will actually work but you are likely to get issues with the tile finish.