Question: Re: Fireplace Liners I am considering buying a wood stove fireplace insert. I'd like it to have outside air combustion. I live in Annapolis, MD. My fireplace flue is 9" (I think) terracotta at about 28'. I was thinking of using either a triple walled (Dura-vent) or double walled pipe where the air space is route for the outside air providing the enclosure around the fireplace is sealed well. One more question, how does one damper the liner to keep cold air from coming down the flue when the stove insert is not in use? Thanks for your help. This is a great site. Answer: Outside air is not usually done in the way that you mention. No need to bring it all the way down the chimney...a small (2-3") hole through to the outside will do the job. Sometimes it can be brought up from a basement or crawl space thru the ash clean out. Make certain you purchase a unit which is set up for outside air. Fireplace installation of this option can be difficult, so be sure that you need it before going to the trouble. 11/2007 As for dampering the flue when not in use... typically shutting the damper and air controls of the woodstove coupled with positive draft will result in little to no cold air infiltration through a modern woodburning appliance.