On Mon, 14 Aug 2006 01:15:12 -0700, mkkbb wrote:

Is it OK to have underfloor heating as your primary heat source for a
room (I'm looking at installing it into my kitchen)?

If so, what type and output would I need to get? I'm only looking at
covering about 9 square metres.

I've done a cheap'n'cheerful one in my kitchen. I had to take up the
(suspended) floor anyway so I insulated between the joists with rockwool
laid on garden netting slung over them, then ran 15mm polybutylene pipe
(Hep2O or equivalent) up and down between the joists suspended just below
the floor level by tiewrapping it to lengths of screwfix builders band
fixed across the top of the joists. Then I laid the new plywood floor and
tiled on top of the wood. The pipe is connected directly into the CH
circuit via a TRV under the floor set to open when the air temperature in
the unheated void below the floor drops to a coldish temperature (I forget
what). In practice the heating is a bit patchy with some areas
feeling quite warm and some cool (to bare feet or hands) but generally the
room is a comfortable temperature in all but the coldest weather.

If I were doing one professionally I'd calculate the heatloss of the room
using the standard method (U values of surfaces + ventilation losses) and
compare the heat output available from any of the construction methods for
UFH for which figures are available to see if it's possible to match
the heatloss. If the room has a large heatloss e.g poorly insulated
external walls and windows and a small floor area (allowing for the area
taken up by units etc) it may not be possible to entirely heat the room
with UFH. In this case extra heating from a radiator or kickspace heater
may be required in the coldest weater. (Depending on how much of a
shortfall there is it may be acceptable to supplement the UFH with an
electric fan heater in cold weater, rather than going to the expense of a
kickspace heater on the central heating.)

Doing it 'properly' one should also fit a separate pumped
thermostatically mixed supply to the UFH so that it runs at a lower
temperature than the main CH circuit.