Please help me make sense of chimney liner & insulation choices!

collins designSeptember 21, 2010

We are installing a Vermont Castings wood-buring fireplace insert into an existing brick fireplace/chimney. The chimney is in the middle of the home (not exterior) and lined with ceramic tile.

This is a DIY project, and money is tight. But we want to do it right. WE're definitely going to install a SS chimney liner (probably flexible due to cost.) Multiple sources say we don't tecnhically NEED to insulate this liner... then again lots of people say we should.


1) Is it OK to buy simply the cheapest flexible SS liner at one of the various chimney-liner places on line? Look like about $275 for a 6", 15-foot kit we'd need...

2) Insulation: it sure looks like using a pour-in insulation like Thermix is a WHOLE lot cheaper, and possibly also easier, than the blanket-wrap stuff. By my rough calcs we'd need only 1 bag of Thermix at $75 versus a blanket-wrap kit at $275. WE're already planning to make a bottom close-off plate for the flue. Is there some reason why the Thermix is not a good idea? I know that we might have trouble getting the blanket-wrapped pipe through the very top of the chimney (which is smaller than the rest of it) so it seems easier to pour something in. Are there other insulation possibilities we haven't looked at yet?

Thanks for any advice!

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If the tile liners in your chimney are in good shape with no cracks, gaps, etc., there's really no reason to install another liner unless you need to decrease the diameter of the flue. Many chimney sweep companies have video cameras that can inspect your chimney for any internal damage.

Many people do install their own ss liners, but it usually seems a good deal easier to accomplish before you start. I'd certainly look carefully at the wall thickness and manufacturers' warranties before picking the cheapest available liner. You also need to be careful in choosing the liner diameter - a 6" liner will not go into a 6" flue, for example. Is insulation necessary? If the chimney is on the outside of the house, yes. If internal, probably not unless the insert specifications call for it.

If they're available in your area, a poured in place liner is another option. Supaflu ( is one system. A mix is pumped into the chimney around an inflatable former and insulates and lines in one step.

    Bookmark   September 23, 2010 at 5:56AM
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collins design

Thanks, mainegrower. We are actually also in Maine. This is strictly a low-budget, DIY situation, so although the Supaflu thing looks intriguing, we won't be doing anything that requires an installer.

I also posted this on, where the general consensus seems to be that for our application (interior chimney) we can get away with DIY-installing a 6" SS liner, an insulated block-off plate at the bottom, and some insulation in the top few feet only. We may decide to pour some perlite in as well, but not the kind with cement, just the loose stuff. Though, presumably it's not needed. The original clay liner looks like it's in fine shape. We do need to decrease the flu diameter for our stove to work well, I think. It wants a 6" diameter flue, and our existing is quite a bit more more than twice that area at 7" x 10.75".

    Bookmark   September 23, 2010 at 8:45AM
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A 7" x 10.75" flue means nominal 9x12 flue tile size. Last year I replaced my old Vermont Castings Defiant with its 8" stove pipe with a Jotul 6" one. I had no problems at all venting the new stove into the original 9x12 chimney using a reducer, but no new liner.

If your particular stove has explicit requirements for a 6" flue all the way up, then you'll have to install a liner, but you might want to check with the dealer or manufacturer before you go to the trouble and expense of liner installation.

    Bookmark   September 24, 2010 at 6:09AM
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collins design

it's actually an older (secondhand) Vermont Castings Winterwarm insert... so I can't ask the dealer! I'll look back in the manual that came with it, though.

    Bookmark   September 24, 2010 at 6:21AM
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