On Fri, 7 May 2010 09:43:04 +0100, Rick Hughes wrote:

Is there any kind of heat exchanger that would attempt to recover
some
of this heat without impeding air flow too much?


Recover what ? .... as you mentioned the air coming in is cold ... you
are not losing heat out through the air brick .... now you are losing
heat elsewhere or no air would be drawn in.

Quite, you can get "draught free" free flow ventilators though. Try a
google on "black hole ventilator" (other makes and models are
available).

--
Cheers
Dave.