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Will a smaller insulated chimney-pipe create draw problems?

michaelprice | Posted in General Questions on

Because my existing brick chimney does not meet the zero-zero clearance insurance specs for Canada, and hasn’t been used for a decade, I am planning on placing an insulated chimney-pipe in for my new wood stove. Unfortunately, a 6″ insulated pipe may not fit the existing chimney, and I have been advised to go with a 5.5″ pipe to ensure it fits.

Might there be any worry of draft (draw) problems with a 5.5″ pipe if my new stove collar (exhaust) is 7″, and my chimney height is 25feet with good outside clearance?

Grateful for advise,


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  1. wjrobinson | | #1

    Stove collar at 7" is huge. For proper insurance coverage it is best to hire a fully insured experienced pro for your install. And all must be inspected in locations like my location.

    If you are DIY and could care less about my above post, you could try it and see how it works. Tall insulated flues that are straight draw very well especially if there are no nearby tall objects, such as trees, mountainsides... I have had issues with lakeside locations too...

  2. GBA Editor
    Martin Holladay | | #2

    Check with the stove manufacturer, but my guess is you can't do it. Of course, you can always buy a smaller wood stove.

  3. michaelprice | | #3

    Thanks to both of you for your replies. I wan't planning on performing the work myself, and certainly will have it inspected for insurance purposes (otherwise I would simply use the existing chimney, which is in good shape). As I see it, I have a gamble on my hands:

    1. I could go with a 6" pipe, which is fine for the stove and should not have draw problems (but might not fit inside the existing chimney, which would be a costly error), OR

    2. I could go with a 5.5" pipe, which will fit fine inside the chimney, but may create draw problems (which would be costly).

    I guess I'm really just trying to weigh my gamble by understanding the full limitations of using a 5.5" insulated pipe on a 7" stove collar.

    Again, thanks for the advice.

  4. davidmeiland | | #4

    I'm confused. What brand of Class A pipe is available in a 5-1/2" diameter? And what reducer would you install to go from 7" at the stove to 5-1/2"?

  5. GBA Editor
    Martin Holladay | | #5

    Any sheet metal fabricator can make a reducer from any size to any size.

    You're right, though: I've never heard of 5.5-inch stovepipe.

  6. davidmeiland | | #6

    Martin, I guess you could have something made, but I've only installed listed, manufactured parts for venting systems. In my opinion the OP should send a drawing of his proposed installation to his pipe manufacturer and get their OK on it. Maybe it WILL be OK, and they might even draw up the custom adapter for him. Otherwise... it's a non-starter.

  7. GBA Editor
    Martin Holladay | | #7

    The stovepipe that connects a wood stove to a chimney or a chimney thimble is usually single-wall blued steel stovepipe. As long as it's 24 gauge or heavier, it should be fine. It's just a hardware-store item, not something that has to come from the manufacturer. Any sheet-metal worker knows how to make 24-gauge stovepipe and adapters. I have often had reducers made by my sheet-metal guy.

  8. billysweet | | #8

    You ask might there be draw or draft problems if you connect your stove with a 7" collar to a 6" or 5.5" liner. (in the trade we call what you are talking about a "liner". You won't find 5.5" stovepipe, but 5.5" liner has been made for years, for applications where the chimney isn't big enough to line with 6", but 5.5" will fit.) In a word, YES. The designer of your stove would have put a 6" collar on if that is what he wanted you to vent it into. That is not to say that it can't work, it is just that you shouldn't be surprised if you get less than optimal performance if you go ahead with this plan. 5.5" is even more likely to give less than optimal performance. The diameter of the flue (vent) and the height of the flue are what powers your stove, so to speak. More diameter and height available to power your stove means you have more to work with when you want it to perform. The designer of your stove chose 7" as the optimal for performance. If you compromise on the amount of draft available by "downsizing the flue," (another technical term) you give yourself less to work with when you need draft. You will want draft most at start up and cool down. When draft is compromised this way, smoking shows up usually at the start up, while the fire is getting going, and, as the fire dies, smoking can also occur. Usually, mid fire, this is less of a concern. Just because you CAN get increasers and reducers doesn't make their use wise. Consult a professional if you think you must downsize. The commenter who suggested a new stove with 6" or better a 5" collar is right on. Sweeps luck to you !

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