Why do you need 3' of OAK, but 25' of exhaust pipe? something isn't right there..
Perfectly fine. As long as the exhaust is fully lined. Harman sells a vented sealing plate extension so it can draw fresh air from the flue chase. (this is on the OP's work order)
, they'll refund the deposit except for the $180 charge for the in-home evaluation they performed.
I would demand to have that "fee" refunded as well.