McGiever wrote:Is this chimney on a outside wall or inside house?
Being only a 3 mo. old install I'd say liner is messed up real bad.
How was liner fastened onto the stove collar?...might be messed up.
If it was mine, I'd shorten up liner to about 4'-5' and seal around fp damper as others have said.
I read this whole thread and agree... draft is the issue, my money is on the fact your chimney is drafting for 2 flu's (one is obviously your stove, the second is your fireplace/house through the unsealed damper opening)... the tighter you make the seal at your damper opening the better draft you will make for your stove (you currently have NOTHING blocking the damper area that you ripped out to get that 6" pipe through it!!! ) most installers use a sheet metal block plate with a 6" hole cut for stove pipe to go through, i used 1/2" rock board and i mortared the sucker in place around the entire perimeter, while still others would simply stuff that open area around the stove pipe with fireproof insulation... the bottom line is you need to block that area with something!!! once that is done....you can then further evaluate (getting mano readings now is a waste of time... you cannot know what your chimney does until you remedy this problem first), your going to need to pull that shyt out and get back in their to do this... once you have that done then focus on the mano install.
I personally never liked the idea of inserts into a fireplace opening and then trying to block the fireplace opening (the fireplace opening by virtue of holding the fire for years generally allows draft failure because of loose brick, shrunken mortar, ash clean outs, etc. AND at the same time 30-40-50% of the heat your stove is producing is behind a freeeking wall and not in your living room! )... having said that... i know thats just my personal belief and many many folks love their inserts! I only wish we caught you prior to the install and it may have saved you some labor but here is a thread showing a sample of how easy this is done (refer to the last photo on the first page in particular)... Removing a Built in damper from fireplace