I am trying to better understand how draft works and am wondering how draft is affected by both the size of the liner and flue exit. It makes sense to me that a stove with a 6" diameter flue and 7" diameter liner would have slightly less draft than if it had a 6" diameter liner. But what if a stove with 6" diameter flue had a 5" liner? Would the draft be greater with the 5" than with the 6"?? Seems like it would then be too SMALL to draft right? I am just curious...
stove draft and liner size
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Many other factors will affect this - such as the stove firebox size, exact interior design, etc.
Many European stoves which use metric would be approx. 5" if converted - and they all work fine.
Chimney draft seems to depend on two major factors, which can be related...or at least have to work together. They are the chimney height and the temp of the gases in the chimney, the second being somewhat related to the size. To confuse the issue more, there is chimney capacity! That is another factor altogether. There is one more factor as relates to fireplace and stoves - We don't just want a good draft, we want enough volume so the stove does not smoke out the door when loading!
All kinds of science comes into play here - the shape of the pipes, smoothness of the internal walls, etc.
My summary would be this - since the measurement and application of all the real calculations would be near impossible, we try to overdo things in order to make certain they work. For instance, a 6" liner for a typical woodstove 30 feet high can handle about 4 times the capacity of most stoves (in BTU's).
It is easier to throttle down a draft that is too strong then to fix one that is too weak!
Main points:
Taller chimneys are best
Less turns are best
Smoother interiors are best
Round or oval shapes are best
Warmer chimneys (insulated or interior) are best.
And then to add to the mess - we need combustion air or the chimney will have a harder time pulling!
Many European stoves which use metric would be approx. 5" if converted - and they all work fine.
Chimney draft seems to depend on two major factors, which can be related...or at least have to work together. They are the chimney height and the temp of the gases in the chimney, the second being somewhat related to the size. To confuse the issue more, there is chimney capacity! That is another factor altogether. There is one more factor as relates to fireplace and stoves - We don't just want a good draft, we want enough volume so the stove does not smoke out the door when loading!
All kinds of science comes into play here - the shape of the pipes, smoothness of the internal walls, etc.
My summary would be this - since the measurement and application of all the real calculations would be near impossible, we try to overdo things in order to make certain they work. For instance, a 6" liner for a typical woodstove 30 feet high can handle about 4 times the capacity of most stoves (in BTU's).
It is easier to throttle down a draft that is too strong then to fix one that is too weak!
Main points:
Taller chimneys are best
Less turns are best
Smoother interiors are best
Round or oval shapes are best
Warmer chimneys (insulated or interior) are best.
And then to add to the mess - we need combustion air or the chimney will have a harder time pulling!
As an example of the above, large European Coal stoves such as Surdiac (60,000 BTU max) all had 5" flues or smaller. The reason is that coal burns more efficiently so less heat up the flue - less heat up the flue=less draft, so a smaller flue will stay relatively warmer and stove will function better.
Taking the opposite end, a Franklin Stove has a massive door opening and will surely smoke if the flue size is choked down. It needs an 8" flue and draft should not be a problem since it is quite inefficient and putting lots of heat up the flue.
Taking the opposite end, a Franklin Stove has a massive door opening and will surely smoke if the flue size is choked down. It needs an 8" flue and draft should not be a problem since it is quite inefficient and putting lots of heat up the flue.
Any one think I couldget by with a 5" liner on my buck model 51? 45000 btu, decent size door, 25 foot masonary chimney. It calls for a 6" but I could do a 5" myself. Other wise it needs ovalized and a brick removed out of smoke shelf to make it fit.
I'm by no means an expert, but with my stove (Regency i2400), I have a 25 ft interior chimney that has a 5.5" liner and it drafts well.
firebuckeye said:
Well, consider it this way - the 5.5 is probably flex, which makes it about 5" equiv or less.
But you might use a 5" flex....which is actually a little less because of course interior walls.
Can you get a 5.5 down there? It is a stock size for flex.
I know it would handle the BTU's, but you have to consider whether it may spill smoke when loading. The other thing would be, if you use the smaller sizes...try to clean it more often as you want it to use the full pipe size. Whereas the 6" might function with 1/4" of soot on both side, the 5/5 or 5 might get cranky.
Is the 5.5 inch inside or outside diameter. I think I could squeeze a 5.5 if it was outside diameter. I never really thought I could do a reline myself but if the 5" would work it would be a piece of cake I think. I am excited about this being a possibility. I would clean it often if I could get this installed.
I have a 6x10" ID flue that I relined with 25' of 5.5" flex liner. I tried 6" flex and couldn't get it down. My draft went from fair to great! Sometimes too great. I couldn't believe the difference. Don't have any problems with smoking when reloading, but I have a bypass and side loading stove.
My thirty foot basement flue is 5.5 flex lined and it has a monster draft even with two 90* elbows in the pipe and a two foot pass thru to the chimney.
I just talked to chimney liner depot and he feels the 5" flex king would be no problem. 25' with stove starter and reducer for 445.00 delivered. Is flex king decent quality. Its only single wall. How doess the price look?
I also measured my door wich is 165 square inches. Is the 1/10 rule apply here. Where as I would need only 16.5 square inches of vent?
I guess it may somewhat apply (hows that for guesswork)
A 5" vent is - what - pie times the radius squared.
about 19 or square inches.
It depends more on the design of the exact stove - smoke path, etc. For instance, a VC with top loading might be a problem.
A 5" vent is - what - pie times the radius squared.
about 19 or square inches.
It depends more on the design of the exact stove - smoke path, etc. For instance, a VC with top loading might be a problem.
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