In article , David Hill david@abacus
nurseries.freeserve.co.uk writes
I have this idea to draw the heat from the top of my Large poly tunnel and
to duct it through a channel of concrete blocks and gravel to form a heat
sink.
The problem is I am wondering if I can get some form of thermostat that will
switch ON when the Temp rises and OFF when it falls.
My local Electrical wholesaler doesn't know of anything to do the job.
Any ideas?

I don't understand the details of what you are doing, but ...

Can you use the thermostat to switch on something of lower resistance to
the thing you want to control and in parallel to it? Then you put the
'thing' on permanently, but if the temperature is too low, the
thermostat circuit is open and short circuits the other. Once the
temperature rises, the thermostat cuts out, closing off the short
circuit and in effect switching the other circuit on.
--
Kay Easton

Edward's earthworm page:
http://www.scarboro.demon.co.uk/edward/index.htm