Help with flue work-around
I want to install a wood stove with a 6 inch exhaust connection vented to my 95 year old exterior wall masonry chimney which is just over 30 feet from chimney crown to firebox of stove. The chimney contains 3 flues each of which appear to be small – either 4×4 or 4×6 inches that are separated from each other by a row of vertical bricks running the length of the chimney. The chimney sweep is going to pass some trials to get the exact diameter of the flue but did not seem to have a problem with downsizing to a 4 or 4 1/2 inch oval liner saying that the long 30 foot draft can make up for the more than 50% decrease in cross sectional area of the smaller liner compared to a 6 inch circular liner. What is the smallest cross sectional flue liner that can be used with a 6 inch stove exhaust? I understand that the ideal would be to have a 6 inch insulated liner but with a 30 foot draft, dry wood etc., how much downsizing can safely be tolerated? Will code be an issue?
Has anyone every slotted the chimney externally to gain access to one of the vertical brick divides, remove the divide between two of the flues thereby recreating a flue chamber that would be at least 4 x 12 inches ? This would allow for insertion of a 4 x 10.35 inch oval liner which is 28.38 sq inches- equivalent to a 6 inch round liner (28 sq inches). I would need a 5 x 11.35 inch opening to insulate the liner. This approach would obviously be costly and not practical from a cost standpoint.
The house has 3 floors plus a finished basement with the main and second floor each being 1700 square feet of conditioned space. The stove will be on the main floor with intent to provide supplemental heat to main and second floor.
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Replies
W. Timothy,
Q. "What is the smallest cross sectional flue liner that can be used with a 6 inch stove exhaust? ... Will code be an issue?"
A. The answer is that you are required to follow the installation and venting requirements of the stove manufacturer. If you have lost your installation instructions, call up the technical help line of the manufacturer, or visit the company's web site.
You shouldn't connect a wood stove to a flue that is smaller than the flue recommended by the stove manufacturer. This is not only good advice; it is also a code requirement, since most building codes require that all equipment must be installed in a way that complies with manufacturer's instructions.
I had a friend who tried to cheat on the size of his wood stove flue. When the air was calm, his wood stove drew nicely. On windy days, the stove would back-puff. He eventually disconnected the stove from the undersized masonry chimney and connected it to a new, properly sized metal chimney.
Timothy,
I'm a homeowner/DIY-er but have burned wood for 40 years and thus have experience with chimneys. Most chimney people seem to think a small reduction in flue size called for by the stove is workable. I have never done this, and would do so warily since one can't know for sure how well it would work until installed and used. I don't have to deal with codes, but I share Martin's reluctance about doing this for his other reasons.
I have a rigid SS liner (6") in my chimney, about 8 years now, with which I am very pleased. I would have liked to insulate it more/better, but space did not allow. The liner went inside an 8" clay liner, which has an inside diameter more like 6.5 to 7". Still is works well with my 30 'chimney, which is not to say I never get a back puff.
When we installed a liner in my son's chimney (one piece, flexible "all fuels" liner which is not all that flexible), i found a mason who could break out the clay liner for extra space (8 x 12 block surrounding clay tiles). Not many folks seem to know or have heard about this around here, even masons, but I helped him do it and it went smoothly (he charged $400 which I thought very reasonable). Your chimney sounds different than block and tile, but you might want to check out that option. We insulated the flexible piece on the ground with a wrap type insulation that was part of the kit, then snaked it down the chimney from above. This also has worked well and is about a 25' chimney. These liners are reasonable cost wise compared to other fixes to chimneys, but I haven't had to pay for labor outside the clay liner removal.
Howard
The mason had a tool that looked like two small steel wrecking balls. These went on the end of a pole which could be added to, and was rotated by a drill. The poles were somewhat flexible but rigid enough to be pushed up the chimney, breaking liner which then fell down and was removed. This job can also be done from above, but after seeing how well this worked I can't see why one would make that trade.
Short of rebuilding the chimney my situation seems unsolvable in terms of wanting to use my chimney with a 6 inch exhaust from the stove. Each of the three flues are only 4x4 without liners. Almost as troubling as not being able to use my chimney is the sorry state of affairs where two CSIA certified sweeps were glad to install a SS liner inside of a 4x4 flue to hook up to the 6 inch stove output with no discussion of the issues involved other than telling me that a 30 foot draft would allow this. One sweep told me that he does it all the time without problems. Certification has no correlation with honesty.
I guess 95 years ago little was standard and folks did whatever worked (and no codes). You must have 3 small compartments made of brick, so I can see why the tool I mentioned would not work as designed. I also don't believe that even a 4" diameter SS liner would fit down your sections. The built up friction from less than perfect dimensions would get hopelessly bound up going down, in my opinion. We had some trouble forcing 6" round liner down 8" square clay liner, and that has more space than what you have.