Hi - I have an older Heatilator fireplace in my house and I'd like to tear it all out and put in a small wood stove. The room is a small addition off the back of our house. The heatilator goes up through a small "attic" space and out to a sheet metal chimney that is square and painted to look like a masonry chimney. After I remove the heatilator is it ok and safe to use this existing "chimney" to run the flue through? I intend to use single wall on the inside of the house and double wall insulated pipe through the attic and out through the roof. I guess I was just hoping to run the double wall pipe this way instead of messing with the roof and buying an attic box when the heatilator already has a metal box through the attic area. Any advice would be helpful - thanks!