Posted: 26/09/2014 at 07:32
I have an 8x6 alminimum glasshouse, with apex roof about 8 FT in height.
My I suggest that you bubble wrap your greenhouse. I don't go completely up to the apex but cross from one side to other around halfway up, so less space to heat. A few years back I tried the following suggestion! which was even better as far as I'm concerned.
Place one layer of double sided bubble wrap directly against the glass held in place by the plastic fittings you can purchase from garden centre. Then add a second layer attached to the end of the fitting in the correct way. Now you have a double skinned glasshouse. Haven't used a heater now for three years, nor lost any plants.
Only expense is initial purchase of bubble wrap, so if you are carefull removing the tape as and where you join sections together, which can last several years with careful use, sticky waterproof tape (yearly purchase)
i also use a marker pen when removing the bubble wrap in spring, where each piece is fitted, so then no need to cut to fit next year.
Many years ago did have a parrifin heater, but found the glasshouse was full of condensation each morning, so always opened the doors to try and dry out. Don't know if they are better now though, so my comment is just my view.
Have an electric heater now, as have laid electricity laid to the glasshouse, used in conjunction with a timer unit, when it is required. Then one can set up the time to switch on and off, saving you a walk up each night.