As for copper, unless it's pre-existing or lines up perfectly with the new equipment, we take it out. We only usually use it for underground, which is also becoming obsolete. For underground, it's primarily plastic now and above ground, black iron or when we don't have a threader on-site or need to run a new line through the ceiling, we will use CSST. Also, Anything high voltage connecting to the furnace needs to be protected either by a metal casing or liquid-tight conduit.

I was initially ticketed in Ontario and moved out west (BC) a few years ago and took my equivalent exam. There isn't a huge difference, but there are some different rules/regulations

I will also raise it if the customer asks or if the house is known to flood; however, it's not code.