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Instead of going through the trouble of core drilling, why don't you take the glass out of the new window and buy a panel for it. Then you can run the vent out through the panel the way it was designed to be done. Core drilling and re-bar are a lot of work plus you will need acetylene torches to cut the re- bar and hopefully you won't damage the core drill when you hit the re-bar. The panel in the window sure sounds less painfull and significantly less expensive.