BigWallop wrote:

"Mike Barnes" wrote in message
news .

Thanks, that's useful stuff. It's actually going to be a *slate* floor
which makes a difference in detail - the slate will be on top of a
substantial new plywood base, and I assume that the heating snake goes
between that and the slates, along with the cement.

I was thinking that slate might feel cold even in summer, which is why I
was considering electric heating, or water heating teed into the DHW
primary. All I want is to take the chill off the stone, because the
towel rail should heat the air OK.

--
Mike Barnes


A slate floor will make a big difference to the system I described Mike.
The pipework would definitely have to go either against, or very close to,
the slate for the heat to transferred up through enough to be viable. And
yet, on a ceramic tile floor, the pipes can be under the timber and it still
seems to allow the heat to radiate through OK.

Weird, but I know that for natural stone, it has to be in very close
proximity to the pipework for it to work with any great efficiency.



This is simply both not a big issue, and not entirely true.

ALL that matters is the relative heat conduction paths upwards through
the floor, and downwards through the ceiling, plus the total amount of
heat being pumped in - which is a function of teh water temp and how
much pipewprk you have.

IF this was a pukka 'in screed' system tou would already have had to
REDUCE water temp because of the dangers of screed cracking. In this
case here, the water temp an be left at CH normal (60-70C?) as teh
airgap between the pipe and the floor will develop a tempeature drop.

Transfer efficiency doesn't matter - in essence the heat is not lost -
it stays in the pipes for other radiators!!!

All you want is a bit of heat bleed from the hot underfloor space up
wards through the ply and slates. That WILL happen.

If that between fllor space heats up tp 60 C or so, do you really think
those slates won't feel warm to the touch?