---------------------------The house, as you say, has been relying on HVAC for overcoming no insulation and vapor intrusion (although, for the vapor part of the equation, the HVAC may not be contributing much to dry-out depending on wall covering or paint type.) 

We just cleared a drain that had some minor root intrusion and the plumber found flushable wipes stuck on the roots causes the blockage.

No insulation or sound-proofing, and water intrusion plus plaster damage from deterioration.

The hydronic is much more cost effective and less intrusive.

Is this the same property that I read About the other day where you were trying to hide water intrusion??

I only use it when I need it2. its "interest only" if you dont like that, just add some money to your payment on top of the interest, thats all an installment loan is.. plus fees.3. so much less intrusive than a regular refi, they just asked for "pay stubs" no 4506-t, maybe i got lucky i dont know thats how it went down. 

A 2 story loft is much less intrusive than a 10 story complex.  

I've done something similar and even more intrusive then your buyer but, I had permission.

I would still consider calling out a third tech if the first two companies didn't agree, especially when the fix is expensive and intrusive.

You can ask questions, in a way that is not too intrusive and asked showing genuine concern.