I’m in Ottawa, Ontario, Canada - yes… it is really cold.
I came across a copper coil attached to the plumbing vent stack. The coil is fed hot water from the tankless heater. I have a good idea what it’s for, but I’d like to make sure. To me it looks like it’s using the exhaust vent stack to help heat the water. Please correct me if I’m wrong.
Location: Basement, furnace room
I’m not sure why the picture is sideways.