Shared gas vent

I’ve looked through the forum and at the ASHI articles and can’t seem to get a clear understanding. I believe the photo shows an incorrect connection in that it should be a wye. When I fired up the furnace and the draft inducer motor kicked in I had air flow coming out of the water heater draft hood. I suspect a problem but need some solid confirmation from a qualified professional.

Tony106_2787 106_2781

I wouldn’t talk about the wye… the furnace (higher BTU) needs to be behind the water heater (lower BTU). Let the expert figure out the rest. BTW, some backdraft when the appliance first kicks in is okay but should go away shortly right after.

Ok. That makes sense. When I considered “smaller appliance connector enters vent above larger connector” I only saw them on the same level in relation to each other; not in relation to the flow of gases. Thanks!

If you Google Category III appliance venting, there’s a very good illustration available.

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