Good luck with them, I put mine in the greenhouse. A while ago listening to a replay of some early radio I heard an old lady recalling how they used to put a candle under a terracotta pot to stop the windows freezing up in the days of single glazed sash windows. I tried it and the whole pot gets warm to the touch, quite hot on top. I had three of them in my 6ft by 8ft plastic greenhouse the other night when it went down to minus five outside. The thermometer showed it didn't quite hit zero all night.