Sometimes cruising round the internet is a good thing. I am always interested in money saving ideas, and do-it-yourself ideas, and came across a discussion for cheaply heating a room in winter. It's a very ingenious thing!
Having watched this video, and several others very like it, I have thought that this could be the answer to all my winter and spring problems in my glasshouse. Especially in Spring, when the days are warm, but the nights are clear and cold, and morning frosts get right into the glasshouse damaging early tender seedlings of tomatoes etc.
I reckon, rather than using 3 x tealights, I could use a longer burning candle, so that I could light it in the evening when I went to bed, and it would keep burning all night.
I was especially interested to hear on one video how during the Blitz in London people used these in their Anderson shelters to keep warm, and even reckon they could boil the billy for tea on one! I'm pretty keen to try that out, just because....