ss chimney liner- smooth vs flex, insulate or not

[Hwood]

Got a wood-coal furnace to hook up in my basement. It will run on its own t-stat with a combustion blower. It will vent through an interior chimney that is centered in the house, thats in good shape, with a 25' run with 4’ above the roof . At this time the attic in the house is not finished but I hope it is in 2-3 years. The brick of the chimney will remain exposed and covered throughout the house for looks. That should give you a bit of a visual. I plan on running a ss liner up the chimney. I would prefer to run rigid down, its a straight shot, BUT it will cost lots more that flex. (I find that odd.) There is 2 other inserts that were in the house when I moved in. One with flex and one with a rigid liner, the rigid side does performs better. This I can see in the draft and when I clean it but this is an exterior chimney and the flex is for the basement insert with a longer run and that might have something to do with it. This brings be to the insulation part. Seems like a good idea to wrap the flue and kits are out there, but there again more money. $250 or so for insulation kit. From what I gather for a proper suggested install in my house I would get ovalized pipe so I will have room to insulate it so it fits down the rectangle (6 ¾ x 12 ) chimney. Looking at $1150 for a full kit to the job. Mind you that’s a flex not smooth wall pipe. No insulation and a 6”round flex kit for $500. I am not against the insulation and think it maybe a good thing considering this unit will fire up as needed and then die way down when heat is not called for, thus having lots of periods of a cold burns. Insulation would help keep flue temps up but could I just use an unfaced fiberglass and pack it down in or wrap it as suggested with wire and just keep it real thin on the 2 tight sides and go with a round pipe. Or with an interior chimney maybe I should just concentrate on the section above the roof line for insulation. Does anyone have some feedback to share?

[Bigsmitty]

Hey Hwood,

Why install a liner at all? If the terra cotta liner is in good shape you should have no problems. The chimney runs up the center of the home. It stays warm enough to use as is. Just check the chimney at mid winter. If the top 5 feet needs brushing then do it. I would prefer to see a 8x8 chimney liner then your 7 x 12 but I am sure it will draw just fine.

If you do decide to install a liner then I would use a 6" round rigid and just insulate the top 5 feet or so. Dont use fiber glass though. Use ceramic wool. You could ovalize the top five feet yourself and that would get you room to use a half inch of insulation. Dont sweep the rigid liner with a steel brisel brush. It will take the mirror finish off it. Use a poly brisel brush.

I would use as is for now and see how it works. I am sure you wont have any problems with it.

[Hwood]

Thanks for the reply. I have to phone the old insurance company and check myself on what they require, I think a liner is on the list. Good point about going round and making it oval where needed. And thanks for the note on the brush and isulation.