Also forgot to ask how long do the gas bottles last?

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Thanks Keith,England,UK.
"keith ;-)" wrote in message
...
I have been running a 2kw electric fan heater in my 10 x 8 greenhouse
which
has cost around £120 for two months keeping
it at 60 f min 24/7.It may have been more expensive than it should be
because I have been running the heater through a thermostat controller set
at 60 f min & the heaters thermostat on full and on its highest heat
setting.After receiving my bill I am trying the heater thermostat lower
and
the heat setting on one instead of two,I think on one its output is 1.8kw
&
2kw on setting two.This has scared me,so thinking of buying a gas heater
supplied with hose & regulator so I think can use bottled gas with it.It
has
a variable output upto 4.2 kw,suitable for 20x10 greenhouse & costs
£99.95p
Would this be the cheapest to run,also would I require permanent
ventilation.If any one is using bottled gas/heater,any advise is
appreciated.
ps just thinking about gas at the moment(panic reaction!)