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DIY downdraft vent

6565 Views 5 Replies 4 Participants Last post by  Bret86844
Support for DIY kitchen downdraft system
Thank you for reading

I'm not in the hvac field but am competent with projects.
In my remodel I am building a kitchen island with a slide in range. Along the left of the stove will be 3" of equivalent counter height up against a backsplash with elevation change of my discretion for a higher counter top to sit on a stool at along that side of the stove.
So my project within is the down draft system I want to build...
In that back splash I would like to see 2 2"x10" aluminum floor vents side by side spanning the front to back length of the stove. These vents I imagine would be up at a height of about 10" above the stove top and 3" to the left.
The vents would be cut into a 3 1/4" x 10" duct running horizontal about 24" directly under the highest countertop. That duct capped on the ends, would T down into either the same size duct or reduce to a 5" round to go through the floor within the wall. The panel your feet kick against will be removable. In the unfinished basement below where the duct comes through I would have a elbow to direct airflow down the joist and outside. After that elbow will be my 8" 800cfm inline fan, switch powered above.
I figure I will have a grease screen close to point of entry.
My questions are, is this rediculous?
Will the suction reach the pots in use on the right side??
Should I have larger floor vents?
Should I have different size duct? I already have the 8" fan....
I thought maybe instead of floor vents I could have something like a kitchen pot filler spout that was extendable act as a periscope for direct suction. Maybe even have slots cut in the sides to catch more steam from multiple points....
Sorry if I am not coming across clear with my thoughts. Any input would be greatly appreciated for discussion.
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First, code requies any ehaust fan of 600 CFM or greater to be interlocked with a fresh air make unit fan. Do you have a make up air fan.

Next, a 5" oval, is equivalent to a 4" round. So you won't get anywhere near 800 CFM through it. Also, a 3-1/4x10 won't move 800 CFM either, unless its a very very strong fan, able to over come more then 2" of duct resistance/static pressure.
Dimmer switches on motors cause lots of problems. You would need a motor speed control switch.

Exhaust with 1x20 openings don't move as nearly as much air as the fan is rated for, and are usually loud.
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