Just a quick update as I ended up buying a gas heater.
First thing is they heat my greenhouse well and its 12 x 10 or pretty close to that. Very nice to be working in now on a cold day.
The only problem I have (as mentioned by Maren above) is that the thermostatic control is not very accurate at all and needs to be set at about 5 degrees before it will kick in. I only really wanted it for frost control and therefore with the milder weather at the moment it is switched off. All Pleione are now potted and will remain stacked up in my conservatory with an electric heater set to frost control just to take the edge off if it gets a little cold. (Conservatory is about 1 degree when its -2 outside).
If you are growing plants that need to be above 5 degrees it's probably a good buy but for frost control your wasting too much fuel. I'm sure there are better/more accurate models out there than the £70.00 EBay one I bought and you get what you pay for.
Looking back would I buy again - No because I do have alternatives and think its cheaper to have an electric heater on frost control than gas going at 5 degrees.
