We are getting ready to pour a new home foundation. Instead of coming back at a later date and core drilling for a stove pipe to the outside, the concrete company is able to place a sleeve while pouring the walls. What size sleeve pipe is best to have placed when pouring the walls? The stove chosen at this time has a 6" pipe. I was thinking of asking for a 8" sleeve or possibly 10" in the event the future stove has a 8" pipe. Thanks.