Noticed a huge difference in draft after switching to 6-inch pipe

Swapped out my old 8-inch flue liner for a 6-inch one last spring on a job in rural Ohio. Before that, customers were always complaining about smoke spilling back into the room, no matter how clean the chimney was. After the switch, the draft improved noticeably within the first week, and I haven't had a single call back since. It really makes me question why so many folks still stick with oversized setups. Has anyone else seen this kind of change after downsizing their liner size?

3 comments

3 Comments

bennett.evan1mo ago

Oh man, I did the exact same thing on a house built in the 70s last fall. That 8 inch liner was just way too much space for their little fireplace insert, and it was like pulling teeth to get any kind of decent draft going. Downsized to a 6 and it was night and day, the smoke went straight up without any hesitation. I honestly think a lot of guys just stick with what they know from the old days without actually looking at the math for the appliance they're hooking up to. It's just basic physics, you need that flue gas to stay hot and moving fast, and a big pipe kills that velocity. Made me a believer, I don't even offer 8 inch anymore unless the firebox really demands it.

the_anthony1mo ago

That's a good point about the math. Bennett, did you run into any issues with the 6 inch liner and that insert's exhaust port size? I've seen some guys just cram a 6 inch liner onto an 8 inch opening with a reducer and call it a day. But that reduction creates turbulence that can actually mess with the draft in a different way. It's like when you try to pour a gallon of water through a funnel too fast, it backs up and glugs. They make adapters now that are more gradual, but not everyone uses them. Seems like the whole system needs to be matched, not just the pipe size.

stellaperry1mo ago

I swapped out an 8 inch for a 6 inch on a wood stove in an old farmhouse and it was like someone flipped a switch. That first cold morning the fire lit clean and the glass stayed clear, which never happened before.

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