First time I've seen this

Hi everyone,

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
Insulation: R12

I’m not sure why the picture is sideways.

Its a Drain Water Heat Recovery (DWHR) which are now required in new home in Ontario. More info at link below:

Thank you very much!

Good to know. Never seen before either.