confused about greenhouse heaters

 

Apologies if this is a recurring post and I haven't looked through past
posts properly.
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 don't
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.
Many thanks!
Paul

 




What are you intending to grow overwinter in an 18 x 10 greenhouse
that you need to heat it to 8 to 10 degrees ?

I'm asking that question because most people work the other
way around. They decide on what they're going to use the
greenhouse for over winter, on the basis of how much its going
to cost them in heating terms.

Have you actually worked that out?


michael adams

...

 



Hi Michael, yes, I know what I want to use the greenhouse for- as for the
cost of running, it is a hobby, hence does not have to be profitable or
particularly cost-effective- and there shouldn't be much difference in the
running cost of heaters with the same power rating (or correct me if I'm
wrong there?) The temperature I want is based on what is comfortable to work
in for long(ish) periods, rather than what is going to be grown, but also a
safe temperature for some insects that are more used to the Mediterranean.
There is also the option of just heating one part of the greenhouse, which
has a partition - but I need some help choosing a heater / type of heater. A
Frostshield 3kW fan heater with thermostat costs £50; a Bio Nevada 3kW fan
heater (with a thermostat & tube) costs £260. A Camplex 3kW fan heater with
thermostat costs £120. Apart from the shape I'm having trouble seeing the
benefits / disadvantages.

 



A one minute Google reveals that the the Bio Green Nevada incorporates
an air re-circulation system which is claimed to save up to 50% of energy
costs, whereas the Frostshield is a straightforward common-or-garden fan
heater.

Both can be found on the following page -

http://www.keengardener.co.uk/heaters.htm


michael adams

...

 


michael adams wrote:

NB You only really need that temperature in the daytime then... and it
would be a lot more cost effective to run in at 5C and wear an extra
layer of clothes. Or work in the greenhouse only on nice sunny winters
days when 10-15C is likely inside.


Unless you really do need something special with a large slow fan or
huge power consumption I found the cheapest 3kW one operated with a
remote thermostat to be perfectly adequate fro a 10'x10' warm end of a
10'x20' greenhouse.


I would take all such energy saving claims with a huge pinch of salt.
The main losses from a greenhouse are leaks and drafts (or essential
ventilation for gas or kerosene burners) and conduction/convection
through the glass windows. Twinwall insulated polycarbonate gives a
worthwhile improvement in thermal insulation as does much cheaper
bubble wrap.

Regards,
Martin Brown