Did you pull a permit for the install of the HVAC system? If so, did it pass inspection?

steel pipe in attic must be double wall type and no screws are needed and not allowed because of the way they lock together.I on occastion if was nervous about the locking of the two pipes then maybe one small screw. If a long screw goes through the inner linner then water can start coming in. you allso create noises because of the inner pipe heating up and outter pipe could can make ticking sounds of pipe exspanding

This is a very large local AC company, so their license/permit should not be a problem.
Coolmen,
you mentioned that water can start coming in if a long screw goes through the inner linner. I was confused since the pipe sends carbon monoxide to the outside of the house. Why water will get into this pipe?

Crosstalk,

I regret if I did not make my question clear to you.

The question I asked has absolutely nothing to do with the HVAC company that you contracted, and their license to operate as a company. My question was did YOU pull a permit from your village, city, or other municipal entity to have them to...

1 Be aware of the fact that you are replacing an HVAC system

2. To have inspectors inspect the final job, and note any issues with the install. If in fact the inspectors find ANY thing incorrect, the contractor needs to fix the problem.

If there is a problem, which you may have, the contractor needs to fix it before you provide the final payment to the contractor.

Remember, when you are replacing a furnace you are dealing with two vital energy sources, namely gas, the other electricity.

Well worth the cost to you, for piece of mind that the install is done correctly.

bpChiI1,
The contractor did say someone will come to do a final inspection in a week or two. I guess that's probably what you mentioned in your post.
Are you saying if the inspector is OK with that, it won't be a problem?
Thanks for the info. It's my first time to get a new HVAC installed so I'm not familiar with the process.

The exhaust gases of the furnace contain water vapor as a result of combustion. Some of this can condense on the inner walls of the flue.

The flue is okay