you have to talk in their language

1) Choose the most common brand.

2) Talk to contractor A,B,C. When you talk to them, never call HVAC guys on a hot day in the summer.

3) Ask the contractor to list what is the specific price for each specific work. It could make you understand each part of the job/price. (It also makes him feel guilty for the quote he gives you).

4) Use A'd price on B, and so on.

95% of 漏 happened at the connections. Make sure the connections are tightened.

Good luck!