On Sat, 9 Jan 2010 09:57:57 -0800 (PST), BlueJohn
wrote:

BTW this is wet (not electric) UFH and it's in bats suspended between
wooden joists (not in concrete/stone).

We have underfloor in concrete downstairs and aluminium heat spreaders
between joists upstairs. Downstairs you feel the warm floor more than
upstairs. If you put a cushion on the floor for about 30 mins how
warm does it feel underneath it?

You can use the cushion and thermometer to map the heat distribution
quite accurately by the way. Simply place the cushion on the floor
for a fixed time (about 10 - 45 minutes, the shorter the better) and
note the temperature on a thermometer placed between the floor and the
cushion. Repeat in a grid pattern across the whole room.