Hello, folks!

This is not actually for a bathroom, but I figure you all are the fan experts. You guided me towards a Whisper fan when I was building my house and I love it.

This time around, I don't need quiet. I need suction! And cheap :).

I want to vent the hot air out of a stairwell, in our no-AC climate. I figure 300cfm will do the trick. The catch is, the ceiling there is slanted (6 in 12) and is only 3.5 inches thick to the roof, no attic.

Is there anything that can do this job?

The house has no ducting, so I can't tap into that, and it's a 1.5 story, so there is no vertical exterior wall in the stairwell above the first floor ceiling.
I guess I could mount a fan on the roof in a little doghouse, but is there a better option?

Thanks much for any suggestions!