hi,i am simulating air flow in house.Now the problem is that how to define the boundary of the door or the window between the rooms?And why?

I don't understand your problem. Just tell Fluent it is a wall. No?

Laika, still orbiting

which version of fluent do you use?

It depends exactly what you want to do. You can set up an "artifical" boundary. If using Gambit, set the plane as an interior. When you see this in Fluent, this plane is in the boundary conditions but it does not affect the results, i.e. You can read values from this plane but the slution acts as if this plane was not there. However if you want this "wall" to have conductive properties etc...I think you set as wall. I dont know how to set up the conductive properties etc.