I know this topic has been raised before, but each person's situation is different, so I thought I would sketch out mine and ask the DIY community for advice and insights.
Our typical Whirlpool gas range sits in our condo's kitchen against a 4" interior wall. There's a microwave above the stove with a recirculating fan system that speeds up the time it takes to stink up the place every time I do a stir fry or sautee some onions. I would like to replace the microwave with an under-cabinet range hood, but there is no reasonable way to run venting to the roof (there's a small office above the kitchen) or an exterior wall, given the direction of the studs in the ceiling.
I removed the microwave the other day and could see an installed piece of 3.25x10" ducting in the wall behind it. The duct's opening faced the kitchen, then did an abrupt 90 degree turn downward, continuing down between the wall studs maybe 7 or 8 feet to end abruptly high on the basement wall, right where it meets the ceiling.
I am thinking about buying a range hood with a 3.25x10" opening in the back of the hood that I can connect to the existing vent, which I can move around a bit to line up with the hood. I would then use an adapter to connect to the duct in the basement, angling downward about 20 degrees, while transitioning to an 8-inch round duct. That duct would continue about 10 feet to the sill of the building, where I'd exhaust it.
To power the system, I would avoid buying a fan blower for the hood, since that would just blow the air directly into the duct's initial 90-degree bend, creating a lot of back pressure. Instead, I'm thinking of installing an inline 600 cfm blower, which would hang from the basement ceiling somewhere along the 10-foot stretch of 8" round duct. The fan comes in a housing so it's easy to connect the round ducting to it.
Thus, the inline fan would suck air down the wall duct, rather than try to push the air down.
Do you think this approach would work? I'm wondering if applying 600 cfm suction to a 3.25x10" vent would create a lot of noise and/or provide good suction within the hood. I should add that the hood I'm looking at has an adjustable knob that lets you infinitely adjust the fan speed, so I could reduce the suction if the noise were too extreme.
Your help is always appreciated!