Two outlet boundary condition for a pipe,
 

For example in a room i hava a pipe, which air went outside through this pide. What can i use for inlet and outlet condition ? i cant make both of them outflow right ? or pressure outlet ?

if you have a pipe in a room and you want the airflow to leave the pipe first and then room then you should define some inlet condition at pipe exit and outlet condition at the room exit.

I know that but the problem is, i have a fan in the room. And i dont push the air to pipe. It is not in my control actually there is no vacuum or anything. I cant upload an image but a few hours later i can :)

Short cylinder in the middle of ceiling is burner. 4 circles are fun which circulate the air in the room and the other long cylinder is for exhaust gas.

So i my question about long cylinder how can i set boundry conditions ? Also i need ideas about how to simulate this model. Firstly i simulate burner and than i will add boundry conditions for all model. Is this correct way ?

Thank you very much,