I am planning on Installing a Vent hood the manufacturer recommends 8 inch duct work.

I am looking for options to make this hole.

1) Diamond hole saw.
I couldn't find a diamond hole saw in 8 inch.

2) Core Drill
But I will get a clean hole. My question is how do I measure the thickness of exterior wall. I have brick which is about three inches. I measure the wall thickness near my garage with brick it comes to around 10 inches. Is this correct ?

  • Is hammer drill out of the question? With a wide bit? We talking square or round duct? Aug 1, 2018 at 15:55
  • There are companies that specialize in cutting holes in all types of brick, stone, or concrete They are not cheap but the do great work
    – d.george
    Aug 1, 2018 at 17:03
  • 2
    3” brick 1.5” air gap 1/2” sheathing 5.5” stud 1/2” drywall= 11” wall you will want to be certain you don’t have a wall stud in the way of your proposed hole. An exhaust vent kit with a damper in it will provide some cover for mild imperfections in your brick hole I generally drill a bunch of small holes around the perimeter of a circle drawn on the brick. Then chisel away the remainder between holes. Use angle grinder to perfect the opening for the duct.
    – Kris
    Aug 1, 2018 at 18:28
  • I am looking for 8 inch diameter square hole. I can use Milwaukee M18 hammer drill but can’t find diamond hole saw with 8 inch diameter. @The Evil Greebo
    – gopal
    Aug 1, 2018 at 18:44
  • Hole saws don’t cut square holes
    – Kris
    Aug 1, 2018 at 21:02

2 Answers 2


1 Roto hammer (rent from local tool rental company) enter image description here

1+ Chisel bit(s) enter image description here

1 8" circle drawn on the surface you wish to cut through

1+ hour of tedious, annoying, possibly painful labor

After you get your hole and ensure the vent fits, be prepared to seal any gaps with concrete caulk, or exterior vinyl caulk, or whatever suits your fancy.


No problem. Just go online and type 8" diamond wet coring bit. You can go to Amazon and type it.

Depending how deep you need the core to be. As you drill, don't forget to wet the spot and when the core bottoms out, take it out and break the round cut part with a chisel inserted on your drill. Remove the debris and keep going.

Expect to pay couple hundred dollars if not more for a decent bit.

You still need a mandrill for the blade of course. These blades don't come with it.

To square off the hole, just use a regular 4 1/2 inch angle grinder disc.

[The measurement on your wall thickness sounds about right.]

Easy as pie.

And there you have it.

Take care.

From Amazon Website Angle grinder blade

Concrete bit

  • OP states in comments that they want an 8" square hole.
    – Ecnerwal
    Nov 6, 2022 at 16:38
  • @Ecnerwal, solution in my answer. Thanks. Nov 7, 2022 at 18:01

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