Witchy wrote in message . ..

My only concern is that because we've built an open shower steam can
sometimes get that high and I might have to fit some sort of fan to
the outside wall. Something to be worried about?

If you do, you're throwing heated air out, like pointing a small fan
heater outside. A crossflow exchanger would mean you retain the
majority of the heat while still changing the wet air for dry.

Regards, NT