Impossible chimney?

I am new to forum, but have been lurking for awhile. At the suggestion of the local stove company I eventually settled on, I ripped out an existing pre fab fireplace and built an alcove to place the new stove in. They quoted me a price for me to do alcove work and them to install new chimney with appropriate firestops, etc and stove install. Due to their horrible customer service I found used Osburn 2300, which is what I was quoted for, and decided to hire chimney person myself. All three companies came and said I cant put class a in my existing chase. I am completely at a loss and any input is appreciated. Going to question stove company tomorrow.

Please see attached photos for better description

begreen said:

How would the installer access the chase interior to install the pipe? It looks like this would require opening up the chase to install the pipe with proper support and firestops.

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All chimney companies that have come asked the same thing

webby3650 said:

It can be done. Drywall removal at the bottom is likely though. Most "chimney" people aren't going to have experience with a retrofit like this, it's going to take an experienced confident installer. Be careful not to hire someone that's just eagar to make a buck.

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We just put up ceiling rock to cove up hole for now. I went with original stove company because theyve been around for years and have good reputation. We shall see what they say today.

superbee69 said:

I am not an expert, but I believe you need 2" clearance from combustables all the way up with the Class A. is there not enough width in the chase for an 8" pipe plus 2" on each side for a total of 12" minimum with the pipe centered?

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Superbee, there was a 12" "liner" in there with single wall 8" chimney pipe inside that originally. Flue for new stove is 6". I was advised we could put class A down it but it would only be supported by ceiling adaptor and chimney cap area. Plus, there would be no fire stops as quoted.

superbee69 said:

what the "liner" made of? is the rest of the chase area just open space? How much work to demolition the interior of the chase just leaving the walls left for a person to build a homemade ladder to go up and down.

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there is a 12" s/s single wall outer liner. It'd be a lot of additional work to remove all and add firestops/supports going in from exterior. It was proposed as a possible alternative to use flexible insulated 316Ti pipe placed inside that liner. Would that be legit?