Thanks for the advice on the ventilation question, I'm following up with my contractor.
I've not followed this in days but many/most heat exchangers have a recirculate fiction, where no air is exhausted or brought in, simply "recirculated". +1 on proper insulation
I gladly would if they would explain what the danger is. I am an Engineer so I think I'm capable of understanding a technical issue if someone tells me what the danger is as opposed to just saying don't do it. On more than one occasion in my career I've been told "you can't do that" by someone who claims to be knowledgeable in a field and debunked the reason. So if you know why it shouldn't be done, please share the technical reason. I doubt you are the type who would blindly take advice from someone just because they claim to know what they are talking about if they weren't able to explain why. I'm trying to do my due diligence so I can make an informed decision
I know only that I've never seen it done and that you've rationalized a number of 'technical reasons' in this thread. So perhaps seek the advice of a Horticultural Food Scientist or similar. At the risk of being Captain Obvious, a woodworking forum is perhaps not the place to seek such a professional.
Or, perhaps just speed on? Your inertia seems well defined.
Out.