Why a chimney pulls
Hot gases are lighter than cold air, so a warm, tall column rises and draws air through the stove. A short, cold or oversized flue pulls weakly. This is why the same stove can perform well in one house and badly in another. Draft is a property of the chimney.
The 3-2-10 rule
US practice asks for a chimney at least 3 feet above the point where it passes through the roof, and at least 2 feet higher than anything within 10 feet. Treat that as the floor, not the target. Many stove manuals state a total height too, often in the range of 15 feet or more, so read yours.
Size follows the stove
Most US wood stoves have a 6 inch outlet, and larger ones use 8 inch. The chimney should match the outlet. A liner of the wrong size in a big masonry flue is a common cause of poor draft and creosote.
Elbows cost draft
Each turn in the connector slows the gases. Keep the run short and vertical where you can, and keep the pipe’s crimped ends pointing down toward the stove so creosote stays inside. Follow the manual on how far a horizontal run may go and the slope it needs.
Questions that keep arriving by post
What is the 3-2-10 rule?
A chimney should rise at least 3 feet above where it leaves the roof and at least 2 feet above any part of the building within 10 feet. It is a widely used minimum. A stove manual may ask for more total height.
Can I reduce a 6 inch outlet to 5 inch pipe?
Not unless the stove manual allows it. Reducing the flue changes the draft, and a smaller chimney on a stove may also breach the listing.
Who should inspect my chimney?
A chimney sweep certified by the Chimney Safety Institute of America is the usual choice in the US. Your local building department handles permits.
Last reviewed November 1, 2026