This could happen regardless of friends or not. This is why we always specify in writing what materials we are using. I.e. Type L copper or ACR copper, ULC 636 venting or Schedule 40 PVC, Black iron gas piping or Type K copper or CSST, 28 ga or 30 ga sheet metal, flexible liner or B-vent or ML liner… Oh, does it keep us out of trouble! Most of the time, but it does go a long way to minimize the miscommunication.

Hi Robert,
Like an old guy told me, you can’t work with your enemies so of course you should work with your friends. Whenever I do a friend’s job, I write up a letter of agreement/ list of work& materials to be installed. I include my hourly rate and shake hands just like I do with any customer.Then we both know what to expect.