On Mon, 30 May 2011 10:20:59 +0100, The Natural Philosopher
wrote:

Hot air systems are very very good at getting a space up to temperature
quickly with very few hot spots.

The one we had in Scotland certainly did that. When it came on the
cat was flung across the room and left clinging to the curtains.
Conversation became impossible and TV could only be understood by lip
readers.

They also are compact.

I'm not sure the 8ft x 4ft x 4ft container of bricks heated by
electric elements which filled what would otherwise have been a useful
storeroom by the front door could by any stretch of the imagination be
called "compact".

Their efficiency and cost depends on how they are driven..

The room the bricks were in was very warm, very useful for helping
epoxy glue to harden. Unfortunately the heat loss during the day
(when no one was in) was such that by the evening nothing much
remained. Fortunately the design was so bad that the large contactor
used to change from peak to off peak had fused shut into the off peak
mode.