chimney rebuild

[jurek]

hello

Due to insufficient draw I’m planning to rebuild the chimney and would like to have your opinion.
I kind of concluded that my chimney is simply too narrow. it has a 18cm diameter and a length of 4m.
The oven has ‘sufficient’ draw with a diameter of only 12cm in the first section.

When I look at some formulas to determine ideal dimensions I get to a diameter of ~23cm with a lenghth of 4m.
Should I simply rebuild with a diameter of 23cm or with a bit of oversize?

Before I’m going to do this investment of mainly ‘time’ im really curious about the opinions of others so please feel free to comment and advice



Thanks
Jurek
Netherlands

 

[jurek]

cant upload any pics please see profile picture

 

[begreen]

I've inserted your image into your post. That's a wild wood drying shed!

It looks like the draft is getting diluted and reduced due to having a common chimney. Mild outdoor temps would make this worse. You might try temporarily blocking off the oven chimney completely to see if this improves draft at the fireplace. If so, the solution is probably for each to have its own dedicated flue or at least some sort of damper to close off the oven when not in use. You could also try to reduce the fireplace opening size by a third with some sheet metal attached to the top edge.

 

[jurek]

thanks begreen,
i've tried both (also at the same time) with little effect.

Last time i tested i had some 'sparking' wood and watched the chimney for a while and notice sparks were coming out very rapidly, while smoke was also coming of the front of the fireplace.
with this observation i conclude that there is 'draw' but i guess not enough to process all flue-gasses.

a diameter of 18cm is obviously to little. but what do i do? go to 23?

 

[begreen]

A general guide for the ratio of fireplace opening area to flue area is about 10 to 1. That is why I suggested reducing the height of the fireplace opening by about a third.

 

[bholler]

thanks begreen,
i've tried both (also at the same time) with little effect.

Last time i tested i had some 'sparking' wood and watched the chimney for a while and notice sparks were coming out very rapidly, while smoke was also coming of the front of the fireplace.
with this observation i conclude that there is 'draw' but i guess not enough to process all flue-gasses.

a diameter of 18cm is obviously to little. but what do i do? go to 23?

You need to have a ratio of 10 to 1 from the volume of the fireplace opening to the volume of the flue. And you need to do what begreen said with the oven flue.

 

[jurek]

thanks, with the 1:10 ratio rule and a pipe diameter of 18cm i would have to more than half-en the opening of the fireplace.
i will do a more rigorous test and close op the fireplace substantially and will let you know how i go.

applying the 1:10 rule to current opening surfaces (oven+fireplace / 0.54 + 0.06 m2) i would need a chimney diameter of ~28cm.
thats a lot bigger than the18cm i now have.

any advice on the length? 4-5m oke?

 

[bholler]

thanks, with the 1:10 ratio rule and a pipe diameter of 18cm i would have to more than half-en the opening of the fireplace.
i will do a more rigorous test and close op the fireplace substantially and will let you know how i go.

applying the 1:10 rule to current opening surfaces (oven+fireplace / 0.54 + 0.06 m2) i would need a chimney diameter of ~28cm.
thats a lot bigger than the18cm i now have.

any advice on the length? 4-5m oke?

The 10 to 1 rule would only work with both if they both had fire in them. You really need 2 separate chimneys. Even if you made it so you could block off the unused one a flue properly sized for the fireplace will be drastically oversized for the oven causing problems

 

[KJamesJR]

I don't even know what I'm looking at. Outside wood fired oven???

 

[jurek]

I don't even know what I'm looking at. Outside wood fired oven???

yes, though its under a roof, but would still qualify it as outside
woodoven and fireplace next to it

 

[FPX Dude]

Wow you stack that high, how do you up/down to get the wood?