Chimney fan renders top rear exhaust fan useless?

[paulie]

I noticed since adding a top blow hole (chimney), much less air comes out of my top rear exhaust fan. Why did that happen? Is this fan now totally useless because of the chimney fan?

[JimmyG]

If your chimney fan has a higher capacity than your top rear fan, the chimney fan will overpower the top rear fan. Also, the air flow path may be more direct to the chimney fan than the top rear resulting in less flow to the top rear. You can play around by changing fans or useing rheostats to control the fan speeds. This way you can find the flow combination that gives you optimal temps.