!Thank you again! and I am using mass flow inlet for the all the inlets and mass flow outlet for all the outlets, because they are all the given data which I get from my professor. And regarding to how to check the mass flow outlets, I used report fluxes after running the calculation, but they are different from the amount that I applied before running the calculation. For mass flow inlets, all are correct. Just only the mass flow outlets are wrong, so in this case, as I think and as you mentioned as well, maybe it is because of the changing of the air density in the domain of the building that can change the volume rate at the outlet. nAnother one thing, there is no balance between total mass flow rate in and total mass flow rate out. Total mass flow rate out is bigger than total mass flow rate in around 7.5%. So it is bigger than what you told me that it should be less than 1%-2%.n