Planning on helping a friend install a vented under cabinet range hood. The previous was a non ducted microwave/vent so, we have to cut holes into the cabinets to run the duct. Surprising to me, the vent requires a 7" round duct. I'm pretty sure the one in my mothers house is only about 4", but it's an old house. Anyway, we had a bit of a time finding all the 7' duct parts we needed at the Home Depot. What we can't find is a 7" hole saw. The biggest HD or Lowes carries is 6". Not to mention we don't want to spend much on a tool we may never use again. Thought of using a jigsaw but the angle would be tight. Any suggestions on how to cut a 7' hole?

 

7" round must be a powerful hood. Most use 6" or 4"x10".

You could use a scrolling sabre saw..... where the blade turns 360° with a handle.
I have a Craftsman one and I think they still have them.

 

What is your path for the ductwork? Most common is directly up through the ceiling and attic. It sounds like you want to go either right or left through the upper cabinets.

Either way, install a 7" to 6" round reducer directly to the vent hood collar, then run 6" from there.
Reducing the 7" to 6" assumes you are not running excessive lengths or you have a professional quality hood.

 

It's a Broan Evolution 2, 30 inch, 300 CFM.

The duct needs to go up thru a cabinet barely 12 inches high, make a 90 degree, and run about 5 feet out to the exterior wall. We can't go straight up due to the second level.

Will look into the 7 to 6 reducer.

Thanks!

 

The diagram I found online seems to show a rectangular duct, convertible to exhaust out the top or back. Yours has a 7" round collar (with damper)?

Broan Evolution 2

 

Most hoods come with a choice for using either round or rectangular duct size.

From Broan....
Choice of 3-1/4" x 10” rectangular or 7" round ducting ensures reliable discharge without re-positioning the blower.

 

Yea, I've installed many of these. You can vent rectangular (only) out the back.

For top vent, you will use the rectangular knock out for 3.25x10. For 7" round, you will knock out both the rectangular and round holes.

Unless it's changed recently, these units come with a rectangular damper. You will need a 6" round damper.