I’ve got a range hood that supposedly moves up to 500cfm (and a gas range so I would like the higher airflow).

It’s about a 6′ duct run with 1 elbow, and I’m planning on using 6″ duct. I could upsize the duct itself, but the location where it runs through the wall is too tight for anything bigger than 6″.

A recent realization is how big of an airflow restriction the vent cap may be. I originally bought something similar to the Seiho-type wall caps, but was looking at their net free area & pressure drop chart, and realized that it probably won’t work well:

Vent Cap – Model: SFX
A 6″ vent cap has only 0.08sqft of NFA (so about 40% of a 6″ duct), and at even 120CFM that corresponds to a 0.3 inwc pressure drop based on their chart.

So far, I haven’t been able to find pressure drop info from other manufacturers. But does anyone have any suggestions for what brand/style of vent cap would work best in this case?

A couple options I’ve looked at:
– 843BL – Broan 843BL – 6″ Round Duct Black Wall Cap w/ Damper
– R2 Heavy Duty Wall Exhaust / Intake Hood | Imperial

Also, have you found there to be a need for the screen if you have a damper? I know it’s extra protection from pests, but the higher the airflow, the more additional airflow restriction from any screening

And, this got me wondering about magnets…do any dampers use them? Seems like it could be a way to get a decent seal while the damper is closed but then minimize ongoing pressure loss once the damper “pops” open (relative to a spring or heavier gravity damper). Just curious.

Thanks,
Ben