In message ,
harry writes
On Tuesday, 14 June 2016 13:59:25 UTC+1, Tim Watts wrote:
On 14/06/16 13:38, dennis@home wrote:

You really don't understand physics do you!

You might, but you've overlooked one thing - see below:

If you put pipes onto and they are at 55C that will only about double
the heat loss through the floor and that loss is only the 1% so at best
adding another 25 mm will take it to the same level as a normal room
without UFH.

Just for the understanding.. if you double the temperature difference
you double the loss. If you double the insulation you halve the loss.


No - because you've incorrectly assumed the substrate temperature under
the subfloor remains the same (your assumption appearing to be about 0c )


This is true of walls and roofs. But the general mass of earth under the
house will rise in temperature with an increased floor surface
temperature, so it is far from obvious how much difference an extra 25mm
of insulation will make.

I've never understood the details, but I can see enough to know your
argument has an error.

Dennis is right on this one.
Instead of a temperature difference of say 20 degrees on an outside
wall, your talking about a thirty or forty degree difference because
its the heat source.

The actual rate of heat transfer varies depending on the nature of the
ground and the movement of groundwater.
The best being dry sand gravel, the worst being wet clay.
You get some of any heat lost back but less then 25% usually

Complex topic.
http://www.sciencedirect.com/science...6013239190066K

Sadly they want money to read that article. Otherwise looks appropriate.

--
Tim Lamb