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Nearly two years ago I bought an inexpensive rocket stove off woot.com (amazon's closeout site), and while it worked okay, it never was as good as it could have been. The efficiency of a rocket stove greatly depends on the 'draw' effect of the chimney and this one - like most commercial ones - had a pretty short chimney.
That short a chimney made it more susceptible to wind than ideal, where a change in wind direction would make the fire tend to lean toward the feed chute instead of up the chimney, so I decided to extend the chimney some. Couldn't extend it too much, as too much would make it top-heavy and prone to toppling. It was very simple & easy; can't claim any major accomplishment on it. The stove is made from typical 4" square tubing, so I went to a local welding shop and for $5 got a scrap piece of 4" square tubing about 9 inches in length, then at the house I bent & attached a band of 1 1/2" metal strap to it and fitted it to the top of the existing chimney. Added some high-temp black paint to protect it from weather, and that was really all there was to it. It fits tight enough that I haven't bothered to screw it to the original chimney, and not sure if I will or not. Have to wait & see if it settles in any or not, and will go from there. Confess I haven't actually used it since adding the chimney extension, but it's still stable which was my biggest concern, and should be nothing but a positive change on how well it draws the fire from the feed chute into the chimney riser.

That short a chimney made it more susceptible to wind than ideal, where a change in wind direction would make the fire tend to lean toward the feed chute instead of up the chimney, so I decided to extend the chimney some. Couldn't extend it too much, as too much would make it top-heavy and prone to toppling. It was very simple & easy; can't claim any major accomplishment on it. The stove is made from typical 4" square tubing, so I went to a local welding shop and for $5 got a scrap piece of 4" square tubing about 9 inches in length, then at the house I bent & attached a band of 1 1/2" metal strap to it and fitted it to the top of the existing chimney. Added some high-temp black paint to protect it from weather, and that was really all there was to it. It fits tight enough that I haven't bothered to screw it to the original chimney, and not sure if I will or not. Have to wait & see if it settles in any or not, and will go from there. Confess I haven't actually used it since adding the chimney extension, but it's still stable which was my biggest concern, and should be nothing but a positive change on how well it draws the fire from the feed chute into the chimney riser.
