Mike Deblis wrote:

We've recently invested in a 10x14 greenhouse that has a cedar frame,
re-inforced glass & aluminium guttering etc. I have run a (protected)
240V supply to the greenhouse.

The north side is close (3ft) from a tall dense hedge, the East is
protected by a timber barn, but the South & West are exposed - we are
on a high hill in Kent. I have insulated with 1200mm wide bubble-wrap
(9mm cell size).

I prefer the wider material. But any insulation pays for itself very
quickly.

We have a load of tropical plants in the greenhouse - some fairly
hardy orchids, tamarinds, cactii etc.

Now I have some tubular greenhouse heaters - Can anyone recommend a
supplier for a good frost-stat? Will I need a fan to circulate the
heat? Would it be better to buy a small (water resistant) fan heater?
If so, where from?

Probably. Otherwise warm air rises and sits in the ridge at the top of the
greenhouse. Some folk double insulate up there to cut losses. My fan
heater was a parasene from a local garden centre. Power was via an ELCB. A
fan stirring the air greatly decreases trouble with cold spots, moulds and
manges.

Am I completely on the wrong track (I'm an electronics engineer, not a
gardener)?

So far so good. If you have room you can cut the heating bill still
further by dividing the blind end of the greenhouse from the door with a
curtain of bubble wrap. That way any drafts from the doors and when you
have to open the door do not take a lot warm air out of the greenhouse.

I kept my heated warm section at 5C and the door end was still just
about frost free.

A friend with some very touchy tropical stuff has a mini greenhouse within
a a greenhouse.

Regards,
Martin Brown