Proper way to re-locate a 6" stovepipe hole and fill the old hole?

[cordsandcordsofoil]

Moved my Fisher stove to the garage and want to install my Mansfield to replace it. The old hole was way too low.
QUESTIONS: What is the proper method for filling the old 6"inch hole? (16x20 cement chimney blocks)
What is the best method for making the new hole in this type chimney block?


THANK YOU!

 

[slow-al]

Best bet is a coreing machine from the local tool rental. Ask for a dry core, the wet while much faster will make a fair mess.
Does the chimney have tile liners? I'd expect they'd crack or break apart with a chissel. mine were above where I went in for the vent pipe.

I used a hammer drill and a 1/4" bit, traced out the circle I wanted and started drilling. When I thought I had enough holes I switched to a larger bit 5/8" or so and took out the middle. When I drilled the 1/4" holes I was expecting they'd be enough, I even went diagonal to connect the 1/4" holes, the larger bit was necessary to break up the pieces.
I don't know about a circular saw and a fiberglass blade but I also tried a 4" diamond blade on a small grinder, parked the shop vac right by the dust comming off the wheel, the shop vac didn't stand a chance, I filled the basement with a very impressive cloud that I'll be cleaning for months I'm sure.

As for filling the old hole, if your running vent to the top thats all sealed you don't need to fill it, if you go with a coreing machine you could plug the old hole with what comes out of the new, assuming it comes out intact.