Sure, send me your email in a PM and I'll forward it after adding a few notes about how it's conceived.Any chance of a copy, I was about to build similar but easier to start from someone else's homework rather than a blank sheet! I'd come to a similar conclusion on air changes, I'd got to about 2kW of heating duty to manage said air changes. I think a forced air system with an inlet/outlet exchanger is the way forwards.