Connecting a Small Wood Stove to a Larger Chimney Size
Ideally, your chimney pipe should match the diameter of your stove’s flue flange. This setup delivers the best draft because the stove was designed to operate with that specific size. But sometimes you need to adapt to a larger chimney - either because you already have a flue in place, or certain project requirements make it the more practical choice. If you follow good flue design principles, you can still get strong performance even with a larger chimney.
At Tiny Wood Stove, we stock a full line of quality flue parts in 3", 4", 5" size pipes and 5" UL Listed Class A chimney pipe, plus the adapters you’ll need to make the transition clean, safe, and efficient.
What’s in this article
- Why matching flue size is best and what happens when you size up
- When to consider a larger chimney and the situations where it makes sense
- Chart: How much can you increase the flue size on your stove
- Special cases and exceptions to keep in mind for small stoves
- Links to related resources and our complete 3", 4", and 5" flue product line
Why Matching Size is Best
Natural draft stoves rely on the rising column of hot flue gases to pull combustion byproducts out and draw fresh air in. The stove’s flue size is matched to its heat output for the most reliable draft. Increasing the pipe diameter too much allows gases to slow and cool, reducing draft strength.
Still, when a project calls for it, increasing your chimney size within the NFPA-211 standards can work well, especially with a tall, straight system.
Decreasing the flue size smaller than the stove's collar (or flue flange) is almost never permitted. Doing so would restrict the flue system to less than required for proper draft, causing smoke to spill out of the air intakes. Per NFPA-211 (the industry standard for residential-style wood stoves which we use as a guide for our stoves as well):
12.4.4 (1) The cross-sectional area of the flue shall not be less than the cross-sectional area of the appliance flue collar, unless specified by the appliance manufacturer.
When to Consider a Larger Chimney
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You already have a solid fuel-rated flue in place
If your existing chimney is in good shape, adapting your stove to it can cut your project cost in half and avoid cutting new holes. We carry 3x4", 4x5", 4x6", and 5x6" adapters to make the transition easy. -
You need UL Listed Class A pipe
The smallest UL Listed Class A size is 5". We carry a full range of 5" UL Listed Ventis parts. -
Availability and shipping costs
In some areas, especially Canada, local sourcing may reduce shipping costs. While 6" is widely available, sticking with our 3", 4", and 5" systems often gives better performance, worth weighing against cost savings.
How Much You Can Increase
The NFPA-211 standard gives clear limits based on whether you’re exiting through the roof or wall.
Roof Exit
Can increase up to three times the cross-sectional area of the stove’s flue collar.
- 3" stove → 3", 4", or 5" chimney
- 4" stove → 4", 5", or 6" chimney
- 5" stove → 5", 6", or 8" chimney
Wall Exit
Can increase up to two times the cross-sectional area.
- Most 3" stoves won’t draft well with a wall exit, even at the same diameter and we don't have any data on their performance when the flue size is increased.
- 4" stove → 5" chimney
- 5" stove → 6" chimney
We stock adapters for all these combinations in our 3", 4", and 5" flue lines.
Wall exits introduce two 90-degree turns and a horizontal run plus more of the pipe is outside, so gases cool faster, and draft is weaker which is why the amount of recommended increase is smaller for wall exits than roof exits.
Related reading: Roof vs Wall Exit Guide
Special Cases
- Heat-robbing appliances like water jackets or heat reclaimers can reduce draft so flue increases would best be avoided in conjunction.
- If your existing chimney is too large to adapt to but in good shape, you can use a solid fuel-rated liner to bring the interior diameter down to match your stove.
Next Steps:
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Use our Kit Builder Tool to plan your chimney with the correct adapters from our 3", 4", and 5" flue systems.
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Read our Roof vs Wall Exit Guide to choose the best configuration for your setup.
i have a 7 inch insulated chimney. Can i use a 6 inch stove with wall exit?
According to the NFPA-211 guideline of “no more than two times the cross-sectional area,” a 6″ stove should work with an otherwise well-designed 7″ or 8″ wall exit. Since codes vary depending on your locality, whether the increase is permitted will be up to your local authority having jurisdiction.
Can I go from 6 in stove pipe to a 4in chimney pipe for small wood stove. Chimney is inside wall
It’s possible but not ideal. Give us a call at 208-352-3417 or email us at support@TinyWoodStove.com and we’d be happy to discuss your specific set up and options. Thank you!
I have and 6in flue in my home for a wood stove I’m replacing with a pellet stove 3in flue. ? Is can I connect 3in to 6in flue?
A pellet stove has different flue requirements than a wood stove, so you’re going to need to consult with your pellet stove manufacturer to determine the best course of action. Pellet stoves are typically positive-pressure appliances that actively push their exhaust up the chimney. A wood stove is a negative-pressure appliance, one that uses the natural draft of the chimney draft to pull the combustion products out of the stove, and pull fresh air in through the intakes. Factory built chimneys designed for wood stoves are typically not totally airtight at the joints because they don’t need to be. If you hook up a positive pressure appliance to a factory built chimney designed for operating at negative pressure, you’ll likely spill combustion products into your living space. If your chimney is a site-built masonry chimney, then it might be OK, but you should check with the stove manufacturer to be sure.
I am putting a smaller wood stove in my existing masonry fire place, can I run single wall stove pipe all the way up the existing brick chimney?
Hi David,
Yes, single-wall stovepipe can work well as a liner when installing a small wood stove inside a masonry fireplace. It’s best practice to use a solid fuel rated liner size matching the stove’s flue flange and to insulate the liner with stovepipe insulation. DIY kits are available elsewhere online that include flexible pipe, insulation, a cap and flashing for the chimney, and an optional tee to connect to the stove’s rear exit.
I have a 7” insulated chimney/ceiling box. Do you have a stove pipe adapter that will work for 5” stove pipe. The chimney pipe is Duravent 7”
Dave-
Thanks for the question. Unfortunately, 7″ is not a very popular size, so I’m not aware of anyone who makes a solid-fuel rated 5×7″ increasing adapter. There are some 6×7″ adapters from other vendors online, so it would be possible to stack a 5×6″ and a 6×7″ adapter. But the cleanest install would be to get a metal shop to fabricate an adapter for you from 24 gauge or thicker steel or stainless steel, and paint it with Stove Bright paint to match the rest of your stovepipe.
Dan; I searched around the internet and came up with the adapter made by Imperial which lists part number BM0068.
Ecco Supply or leacock coleman might have stock but haven’t contacted them.
Thanks for sharing your findings, Dave! That part looks right to me.
I have a 10” flue and a 6” wood stove pipe……Can I do 10-8 and then 8-6?
Hi Sean, as a rule, you don’t want to adapt your stove up more than 2″ for a roof exit and 1″ for a wall exit. Going from 6 to 10″ (even using some pipe with an 8″ diameter), will cause major draft issues for your stove.
Ugh thanks for the feedback…that’s such a bummer….I have a very steep roof line, and was hoping not to have to put myself in a position to have to run a new 6” pipe down thru the 10” pipe…..
Hi there, I am trying to do 3″ to 8inch chimney exit – is this possible? I saw maybe I can do a liner? how do I go about this without it being totally sketchy? Thanks.
Thanks for the question, Cydney. Yes, the only way to do that would be to run a 3″ liner from your wood stove, through the existing chimney, to the top of the chimney.
Hello, I have an 8” flue wood stove in a cinder block garage. So it’s a 2 foot 8” vertical section then a 8” 90 through the block wall to another 2 foot 8” stove pipe section then it has a 8” to 6” reducer and then a 6” 90 with a 6 foot vertical 6” stove pipe going up. Is that 8 to 6” going to cause huge issues. It was originally all 8” but after it rusted out I couldn’t find everything I needed to keep it all 8” to I decided to reduce to 6” but now reading some stories that has me thinking I may have screwed up here. Smh. Any suggestions?
Hi Paulie-
Thanks for the question. What you’re describing is an 8″ wall exit reduced to a 6″ chimney on the outside. Unless your stove manufacturer specifically says it’s OK to reduce to 6″ (very unlikely) then this configuration is not going to work. While it’s sometimes OK to use a larger chimney than the flue flange size, it’s almost never permitted to reduce the chimney to a smaller size. Unfortunately, you will need to remove the 6″ pipe and replace it with a properly sized 8″ Class A chimney system.
i have a old french stove with a elliptical hole for flue is it safe to blank plate the shape of this hole and increase from the stove a 4 inch flue collar adapt
to 5 inches to go up a flue pipe straight out to chimney
Thanks for the question, David.
If you have an elliptical flue flange, the best practice is to take a piece of single-wall pipe and bend the bottom end to conform to the elliptical shape. To do this with our pipe, you need to cut the male end off the bottom to make the pipe flexible enough to bend. Keep in mind, sometimes the stove’s flange is male (the pipe goes outside of the flange), sometimes it’s female (the pipe goes inside), so you may or may not need to re-crimp your pipe once it’s the right shape.
Regarding your proposal, I would be concerned that adding a blank plate with a round hole would effectively reduce the size of your stove’s flue flange opening, which could prevent the stove from functioning properly. It would be much better to modify a pipe to fit your stove rather than modifying your stove to fit the pipe.
I just bought an old antique wood stove made from cast iron. The exit for the pipe is 3.1 inches wide (8cm) and I cannot find any fitting pipes.
I saw that you offer a 3 to 4 adapter. But I assume at the more narrow part it is not adapter right? Asking as mine is 3.1…
When searching online I am flooded by pipes the size for pellet stoves only.
Thanks!
Thanks for the question! If the inside diameter of the flue flange is 3.1 inches, then that’s standard a 3 inch flue flange and our 3 inch flue parts should fit nicely out of the box. There’s always a bit of variation between manufacturers, so having a diameter 1/10″ over the standard flue size is unusual. Using a 3″ flue system on this stove would not be considered a flue size reduction.
If you do find that the pipe is a bit too loose in the flange, you can use the thicker stove cement that comes in the tub to fill up the gap. Look for Hercules brand High-Heat Furnace Cement, Rutland 2000F Furnace Cement, or a similar product at your local big box hardware store.
And to answer your other question for anyone else reading, yes, our 3×4″ adapter is for connecting a 3″ stove to a 4″ flue system, not the other way around. The 3″ part is the downward pointing male end, and the 4″ part is the upward pointing female end.
I have a 4in tiny stove that I need to adapt to a 6 in through wall chimney. I have the 4 to 6 adapter, and want to ask where would be be best application to make the change to the 6 inch. Should I run 4 in pipe to the adapter just before it goes through the walll and into the chimney? This would mean the adapter is horizontal, which mighty be a create problem.. Or, should I run 6 in pipe to past the elbow and then adapter at the bottom of the elbow (a more vertical position). Then run about 36 inches of 4in from the adapter to the 4 in stove collar? I’m not sure what the best option for draft and safety would be. Thanks for any information you might lend on this.:)
Cathe-
It sounds like you’re trying to adapt a 4″ stove to a 6″ wall exit, which is not advisable. The combination of the increased volume in your flue and the elbows in a wall exit will likely be too much for your small stove to overcome and you will experience a poor draft and inefficient burn. In any flue design where you’re increasing the pipe diameter, it’s best to maintain as much pipe as possible that matches the stove’s flue flange diameter.
I just bought your 5K. I need to adapt to 6″ at my wall/chimney. Your photo shows the increase after some 5″ pipe. Is that the 20″ x 5″ pipe you are using?
Yes, that is our 20″ length. The higher up you can convert to a larger diameter the better. If you can use the 40″ length or more, it will reduce the overall negative impact of increasing the flue diameter. If you have more questions, don’t hesitate to reach out to us at Support@TinyWoodStove.com