We had a thread a while back generally lamenting the accuracy of the thermostats
built in El Cheapo greenhouse heaters. Well you get what you pay for - if you
are prepared to pay (a *lot*) more I noticed at least one offered in Two Wests
& Elliot's new catalogue which should give very acceptable control. The energy
savings ought to recoup some of the cost but above all you will be confident
that your plants are safe. They do two - one has a traditional capilliary
thermostat (not bad), the other has an electronic thermostat with a remote
sensor (*much* better), tho' the resolution and accuracy aren't specified it
should do the job.
http://www.twowests.co.uk/cgi-bin/twowests.storefront

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Rod
http://website.lineone.net/%7Erodcraddock/index.html
My email address needs weeding.