Motorized Damper for Range Hood Exhaust
Why is a motorized damper always used/advised for makeup air, but nobody seems to use motorized dampers for the hood duct? It seems better for a tight home than a typical spring loaded backdraft damper, because it would close tighter. And in addition to less air leakage, it would also keep more cold out in a cold climate. Is there a negative to a motorized one?
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There is a typically a large difference in pressure developed across a powered vent and a passive vent. Which is why the passive vent has to be far larger.
With the best design - powered intake and exhaust, the damper could be the same design on both.
A spring damper won't work for the makeup air vent. It would never open. So motorized is the only option there. As to why not motorized at the other end, it costs more in time and materials.
At the same time, most spring dampers are a joke.
Spring and balanced dampers require a certain amount of air pressure to operate. In the outlet from a range hood, the full force of the fan is pushing the damper open. With a makeup air inlet, the damper only sees whatever fraction of that airflow is not coming through all the leaks in the home (and there are always some), so it doesn't see the full force.
Spring and balanced dampers tend to be less reliable too. Dirt and grime can make them stick, and since they have to be able to open with tiny amounts of air pressure, they can't close very forcefully, either (thus the leaks). Power dampers don't have these problems -- they have motor actuators that can force them open and closed regardless of airflow, and they're strong enough to have tigher seals, so less leaks.
In my generator room designs at work, I always spec power dampers for in and out air since they're much more reliable than the air pressure operated kind. If you have the choice, a power damper is better in nearly every way.
Bill
I have wondered the same thing - and also for bathroom fans. Anything on an upper floor will let warm air flow out, so a gravity backdraft damper would just open under the positive pressure. A motorized one would prevent this.
Only negative I can see in a range hood would be the works getting gummed up by oils, but that is just as likely on a non-motorized damper too.