# How do I determine what size flue pipe to use on my homemade wood stove?



## Blue55b (Dec 8, 2016)

I recently built a wood stove for a friends garage and are having problems with smoke filling up the garage where it is not drawing properly. It was built using an old vat. It is 30" around and about 5 to 6 foot tall. It has a 6" flue going straight up out from the top then to a 45 through the wall and then back up. Is 6" to small? Any help would be appreciated, thank you.


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## rwhite (Dec 8, 2016)

How long is the flue?


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## BenTN (Dec 9, 2016)

That's alot of firebox. I linked a calculator for bbq pits, It gives an idea of flue dimensions.

http://www.feldoncentral.com/bbqcalculator.html


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## Blue55b (Dec 9, 2016)

rwhite said:


> How long is the flue?


Around 14'


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## mellow (Dec 9, 2016)

That is a lot of firebox for 6", most of that size are run on at least 8", sounds like your draft is suffering if you are getting smoke spillage.  I would try extending your pipe another couple feet and see if that helps.

Are you using single wall then converting to Class A?


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## lhuffhines (Dec 9, 2016)

FWIW, on our Stoves and Furnaces we use a 6" flue on units that are 7.1 Cf fireboxes or less. More than that and we use an 8" flue. We do offer one stove that is a 3.5 with an 8" flue.


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## Blue55b (Dec 10, 2016)

mellow said:


> That is a lot of firebox for 6", most of that size are run on at least 8", sounds like your draft is suffering if you are getting smoke spillage.  I would try extending your pipe another couple feet and see if that helps.
> 
> Are you using single wall then converting to Class A?


I am using 1/4" wall welcasing for the flue.


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## bholler (Dec 11, 2016)

Well with that size firebox I would say you are in the 12" to 14" range for the flue.  No way that 6" will work.


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## BenTN (Dec 11, 2016)

1/4" is a lot of steel to warm up. in my experience building bbq pits with heavy steel, it takes a lot of heat to remove moisture and heat the steel to temp. if this garage is not kept at temp and is allowed to cool completely there may be considerable condensation inside that system. can you build a small hot fire directly under flue? I assume it's a top vent without baffles. Think path of least resistance until all that steel is 200 deg or higher. I would think it would draw like a rocket stove once it's hot. maybe post some pics of the stove and flue.


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## bholler (Dec 11, 2016)

lhuffhines said:


> FWIW, on our Stoves and Furnaces we use a 6" flue on units that are 7.1 Cf fireboxes or less. More than that and we use an 8" flue. We do offer one stove that is a 3.5 with an 8" flue.


Yeah but this one is 25 cubic feet.  


I am curious what material the firebox is made of.  What type of clearance do you have?  what size space are you trying to heat?


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## rwhite (Dec 11, 2016)

bholler said:


> Yeah but this one is 25 cubic feet.
> 
> 
> I am curious what material the firebox is made of.  What type of clearance do you have?  what size space are you trying to heat?


Maybe  my math is wrong but a circumference of 30" is a radius of 4.77"
4.77x4.77x72"x3.14= 2.98 cuft (5143 cu in)


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## rwhite (Dec 11, 2016)

rwhite said:


> Maybe  my math is wrong but a circumference of 30" is a radius of 4.77"
> 4.77x4.77x72"x3.14= 2.98 cuft (5143 cu in)


That's if he truly meant "30 around" , if it's 30" diameter then he is up around 29 cu ft.


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## bholler (Dec 11, 2016)

rwhite said:


> Maybe my math is wrong but a circumference of 30" is a radius of 4.77"
> 4.77x4.77x72"x3.14= 2.98 cuft (5143 cu in)


Ahhh I didnt read it that way I took the 30" as diameter not circumference.


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## Blue55b (Dec 12, 2016)

BenTN said:


> 1/4" is a lot of steel to warm up. in my experience building bbq pits with heavy steel, it takes a lot of heat to remove moisture and heat the steel to temp. if this garage is not kept at temp and is allowed to cool completely there may be considerable condensation inside that system. can you build a small hot fire directly under flue? I assume it's a top vent without baffles. Think path of least resistance until all that steel is 200 deg or higher. I would think it would draw like a rocket stove once it's hot. maybe post some pics of the stove and flue.


Have tried a small hot fire for warm up purposes with no luck. I will post pics tomorrow.


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## Blue55b (Dec 12, 2016)

rwhite said:


> That's if he truly meant "30 around" , if it's 30" diameter then he is up around 29 cu ft.


It is 30" diameter.


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## bholler (Dec 12, 2016)

Blue55b said:


> It is 30" diameter.


Yeah you need a much much larger stack on that.  What material is the firebox?  What clearances to combustibles do you have?  and what size space is this meant to heat?


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## rwhite (Dec 12, 2016)

How big Is this garage your trying to heat with this monster? Basically you have 10 large wood stoves venting through 1 pipe. Any pics of this beast? He's gonna need a cord of wood every time he wants to change his oil


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