Tools and Accessories to make a hole 7" duct

[rylim]

Hi, I will be installing a new range hood in my kitchen and have to run a 7" duct piping through the ceiling to the roof.

Therefore, I just what tools I can use to make a perfect hole for the duct? I tried to look up for a 7" hole saw but no luck. Any suggestions here?

 

[TomGadwa1]

Use a compass! Set to 3.5 inches. Point in the center and the tip on the radius and draw your 7 inch circle!

 

[RussellS]

Use a compass! Set to 3.5 inches. Point in the center and the tip on the radius and draw your 7 inch circle!

Yes.  And then get a spade bit and drill a hole inside the circle.  Then get a jigsaw or manual keyhole saw and cut out the circle.  Keyhole saw if you are cutting through drywall into the ceiling.  Electric jigsaw if you are cutting through sheathing on the side of the house or roof.

 

[live4ever]

Lots of low-tech ways to do this for a one-off task, but if you have frequent need to efficiently drill perfect holes of large diameter take a look at Hole Pro (there are many similar and cheaper knock offs - just make sure you're looking at ones with replaceable and carbide blades). 

 

[Cheese]

I had to do the same thing for an 8” vent for my range hood going through the side wall. Keep in mind that it’s nigh to impossible to cut an exactly round opening with a jigsaw and sometimes the vent pipe is also not exactly to size and also exactly round. You’ll also want a little slop in the cutout to get everything aligned and not have something binding.

Measure the pipe, add a little room for slop, draw the circle with a compass and make the cutout with a jig saw.

Fabricate a cover of the material of your choice to cover the slop room and to give the penetration a more finished appearance. I fabbed the one shown of 304 stainless sheet.

 

[semenza]

Not sure if you are going through the roof but if so, and the pipe is not perpendicular to the roof line, don't forget that the hole  needed will not be round.

Seth

 

[John Beauchamp]

Don't forget to check for ceiling joists in the way. You might need to transition to 3 1/4 x 10

 

[Peter_C]

Don't forget to check for ceiling joists in the way. You might need to transition to 3 1/4 x 10

That is microwave size and my preference if going thru a cabinet so it can be covered in a wooden box.

The Klien tool is supposed to work for 7" holes in drywall. Here is the link. I believe Milwaukee rebrands as I am sure others do too. They work just okay.https://www.homedepot.com/p/Klein-Tools-Quick-Cutter-Adjustable-Hole-Saw-53731/203828012
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[Bob D.]

A Roto-zip type tool with compass attachment might be a good choice for this task.
There are corded and cordless versions available from multiple manufacturers.

 

[cpw]

I had a 10" duct to install for my range hood. It's not quite the same because I went horizontally.

For the holes in the cabinets I used a Trion with the circle guide.

For the siding of the house I used a reciprocating saw to make a square hole.

 

[Cheese]

[member=60624]rylim[/member]

FWIW...while rummaging around for info on router bits, I just noticed that Whiteside does manufacture a carbide tipped hole saw that will cut a 7 1/4" diameter hole. Whiteside #8007250K.
https://www.whitesiderouterbits.com/collections/self-clean-hole-saw?page=2