Posted: 08/02/2014 at 13:19
The electrician said it would use about as much as a 100 watt bulb.
100W does not sound good enough. Most GH heaters tend to be 2KW. Sounds like you get away with it this year as it has barely got below 0C and that it is a lean to to a house, so gets extra temperatures, but I think if you have a 100W heater then when the temps fall below -5C then you will get frost in the GH.