[Gwiz]

i shouldn't worry too much then.

[SnooziSuzi]

I have a 'large' propane heater for my GH that I'll be putting on in a few weeks time to start some seedlings off.  If they're set up correctly they don't so much keep the GH warm, just enough to stave off a frost.

Mine ran for a whole week on one tank (is the bigger (2 chimnied) version to this one; usually about £30 from most diy stores).

[Ferris]

This may be a bit more of a project than you really want to take on, but having read about it, it is something I would love to try but dont have the time at the moment.

I have got the Dick Strawbridge book "It's not easy being green" and he talks about a very clever system for heating a greenhouse which involves using a heat-retaining material like broken glass in a trench or layer at the bottom of the greenhouse and then heating that up rather than the air directly. He also goes one step further by using a simple convection method with a small fan and some smoke liner which (in summer at least) 'sucks' hot air from the top of the greenhouse and blows it back into the glass trench at the bottom... then over night the heat is slowly released out of the glass to maintain a good temperature over night.

Cant remember the exact details but if you were feeling adventurous then could be worth borrowing or buying the book?