To respond to the load calc's, yes they have been done in past and they say 5 tons should work. If you want the whole story on my home, search site under CARESTX and read my old string "New Zoned System Trouble"
As for the new system quotes, I assume each of the groups I have had give me quotes has done their own load calculations and so far each has come back in between 7.5 and 8.5 tons.. Grant it, I am filling them in on the history of the old system as noted in Steve Wiggens post.
I will add a comment to the old string just to throw it back up on the board and in play.
As for the who am I using for bids, I would feel like I was promoting one over the other at it would be premature at this time to do so but will post a # if you would like to call me off site.
Can say that I have used the ACCA web site to start and cross reference "for what it's worth" the BBB site.
As this is my second time around and found this sight and it's members so usefull last time (see post) I place alot of trust in the comments received.
Please keep them coming...