"Martin Brown" wrote in message
oups.com...

Easynews wrote:

I am trying to decide which electric heater to buy for a fairly big
greenhouse (18' x 10') but a quick look at TwoWests catalogue shows 9
different heaters which vary from £41 to £259, and I can't see what is so
different about them to warrant the huge price difference. The choices are
(a) tubular heaters which fair enough are different, (b) fan heaters with
tubes (c) fan heaters without tubes. Has anyone any recommendations?

I prefer a fan heater since it stirs up the air and prevents cold spots
developing.

really have roof space to hang a heater, it will need to go underneath the
benches, and I just want to keep the temp. through the winter at 8 to 10
degrees C. Heaters would not be used in summer.
The greenhouse is well insulated.

It had better be! Heating it all to 8-10C will cost you a fortune!!!

Far better to keep the closed end of a large greenhouse screened off
and fully heated, perhaps with a warm box inside for the really touchy
equatorial species. Then with luck the end near the door will stay
approximately frost free. My 3kW heater struggled to hold 5C minimum at
the warm end when the outside temperature was -12C or lower.

And you need to have a backup plan for mid-winter snowstorm power
failure.

Some experimentation with surplus seedlings to see how temperature
sensitive they really are is also worthwhile. Books generally err on
the side of caution.

Plants that are permanetly disfigured by cold like cacti & succulents
are a gamble. Small ones often are more sensitive, but wrecking a large
specimen plant is a bigger loss.

Regards,
Martin Brown

Thanks Martin. I have an 8 x 10 partition at the opposite end from the door.
We are on the coast, and temperature very rarely falls below -4. Power cuts
have been taken care of! Unfortunately I have around 300 baby cacti some of
which are very fussy about the cold- plus a few insects that I want to keep
happy. What do you think of the heaters with / without tubes attached?
Paul