Chimney limitation

Hi all,

I have a 6 inch wide and 40 foot long insulated and straight up steel tube chimney. The draft is very good (almost too good). Can I build a 7 or 8 inch batch box or do I need to stick to 6 or 6.5 in order not to get problems / sub optimize?

Thanks!
Henric

Hi Henric;
Can you partially replace (without bureaucracy issues) the indoor portion and increase its size?
You might be able to build a 7" if you can increase your interior pipe size, and leave only the 6" penetration thru the roof.
If not, I will tell you that a 6" extended-length batch really puts out the heat. Increasing dimensions to 6.5" as Peter suggested would make a fine batch box.
You sure can try pushing a 7" batch thru your 6" pipe but it might cause issues.

Thanks Thomas!

Unfortunately, my house was built 1900 and the metal flu has been inserted into one of the original pipes in the brick chimney. Thus, it's 6 inch from roof to basement without any chance of making it bigger unless I rip it out completely... So... then I will have to stick to a 6-6.5 inch build. Though, you say that it is possible to make the depth of the burn chamber longer without compromising the efficiency? The recommended fire box depth for a 6 inch is 432 mm (sorry, I don't have the measurement in inches in front of me). Do you know how much I can extend the depth?

Best regards,
Henric

Hi Henric;
25% length increase is acceptable with Peter.
So up to 540mm is allowed, I suggest 500mm  (20") as a good length.

Thanks! Then it's settled. Will start building this weekend 🙂