Drafting
condensation
frequency of inspection
warranted listed product

So many reasons not to use single walled in inaccessible, outdoor, unconditioned spaces. Don't forget in attics you 75% offset rule: for every 3 feet of horizontal offset, you need 4 feet of vertical and that's a minimum std.---does not guarantee performance. Also, use listed supports and components. If the chimney is unsuitable, it must be relined with a listed liner or, if allowed by mfr, B-vent inside chimney.

Bob

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disgusted with some people on this forum. Out of here!