oliver power wrote:I've only read page one of replies. After posting my reply, I'll more than likely read the other pages. I'll give you my experience/opinion. If you can find a 6 inch diamond hole saw, that's the way to go............ALL THE WAY THROUGH. Fast, neat, clean, and done. Myself, I've used a hammer drill. Draw a 6 inch circle. Then a series of 1/4 - 3/8 inch holes around the circle, through the block. Drill some holes in the center of the circle to weaken some more. Then carefully tap out the block with a drilling hammer (small sledge). NOW, you still have to put a hole in the flue liner. That may be difficult (But can be done). Depending on how hot the tile has gotten, you may go through many masonry drill bits. If you try drilling through the block, and tile all at once, you'll smoke bits left & right. Do the cement, then the flue. The next time I do what you're trying to do, I'll find me a 6 inch diamond hole saw. You'll want position #1 in your picture. You'll hit webbing in position #'s 2 & 3. I like the sand idea, but not necessary, Especially with a hole saw. Oliver I also like the water spray idea.
This is how I would do it. And how I've done similar.
Had to put a range hood vent in when I rebuilt the fiancée's kitchen. Her house exterior walls are cinder block with metal lath and stucco.
Using my Porter-Cable 1/2 inch combo drill/hammer drill, and a new 3/8 inch masonry bit, I just made a series of holes about an inch apart, centered on the drawn outline of the vent duct.
Then I played "connect-a-dot" with a cold chisel to take out the remaining bits of block between the holes.
You'd be surprised how quickly a new masonry bit in a hammer drill goes through cinder block and brick. And how easily the raggedy edge of that opening can be caulked around whatever metal tube is put into it using refractory cement.