Hi all,

I am adding a bathroom right next to this heat pump water heater. I currently vent cold air from the heat pump up through the old gas furnace vent (which is also now a heat pump, don't worry) through the top of the roof.

So, I want to tie in the 4 inch bathroom exhaust fan to this current setup at the top. My concern is to prevent the exhaust from the bathroom/water heater from blowing the other way. Which fitting should I use for this application(wye, T,)? I could easily vent out the side of the house, but would rather avoid the penetration if possible.

Picture to illustrate my current setup (water heater is pulled out currently, but I would tie in above the flexible vent tube.

Thanks so much for the advice!

https://imgur.com/cDUWW6O