Variable temperature constant volume the laws of physics are against you when the transfer is to air. Lower temp on the water side and all you'll end up with is a draught (and associated cooling process) rather than just a lower discharge air temp, down to a point. Picture the curves on a...
Thanks for the tip, rang them and they advised we phoned eco-equipped. So we did and we have now ordered.
And no need for 'uni strut', whatever that is!