I’ve searched through multiple posts and read some charts and can’t find an answer to this specific scenario. 2 50 gal water heaters share a flue with a 89,000 BTU (output) furnace w fan assist. I know smaller BTU should tie into flue downstream of larger unit but would you add the total BTU of the water heaters? The water heaters may or may not be running at the same time. Correct or not? I’m thinking not but need conformation. Thanks in advance.
Regardless, those are not factory wyes. Refer it out for correction for safe operation.
You are right about the water heater vent placement, if I had to vent them I would do it like this, but leave that decision for the qualified person you refer it to.
I think one is gas and the other is electric
That is Mark’s reply, OP shows venting for three appliances