"Theo Markettos" wrote in message
...
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.

If it is as bad as you say ... change to a room sealed boiler, a small
balanced flue model may solve your problem.