I am working with fluent in natural ventilation problem, with Boussinesq aproximation. I have a heat source, and I want to get solution without definning inlet and outlet boundary conditions. I think that the heat source must to force the air flow within the domain. Is it possible to simulate with fluent? How? I don't want to define velocity or pressure at the inlet, because I think this seting will have a decisive influence in the flow field.

You will have to set the pressure for the inlet. FLUENT will deal with the elevation effects automatically. The inlet pressure will not have a big effect.

I define pressure-inlet with 0 gauge total pressure at inlet, and 0 gauge pressure at the pressure-outlet.

Thank you for your kindness