Shouldn’t the WH vent be higher than the Boiler? Boiler on Rt, WH on Lt. Ok to use a “T” this way?
My gas code book says you are right, they must enter at different levels. Largest on the bottom. Using a double base tee here is the way to go, it will provide a clean out which is also required.
Do you mean something like this Erik?:
Yup, but welded stainless may be a little over the top They come in single wall, often aluminum or B vent if there is less than 6" clearance to combustible.