On Wed, 02 Feb 2011 17:42:35 +0000, Andrew Gabriel wrote:
Then when we had a really cold spell and it was more like -5C outside, I
tried it and found it worked fine, without doing defrost cycles. So
there's a window from something like -2C outside to +5C outside where
it's inefficient due to defrost cycling (blowing large clouds of fog
across the back garden), but above and below this window, it works fine.
I don't know what the absolute lowest it works at is, as I've not tried
experimenting.

I think they're generally thought to stop working at around -20C (which
renders them useless where I am; it was a nipply -34C this morning)

cheers

Jules