draft

[barneshilary]

Hi first posting.
I have a question about draft on a wood boiler. I am installing a wood boilerin my garage an the boiler has a 7" flue. I have a lot of 6" metalbestos already. I was wondering if I can use the 6" chimney that I already have? Should I install a draft inducer? Or should I get all new pipe?

 

[jebatty]

What does the installation manual say about flue size? For example, the manual for my Tarm says either 8" or 6".

 

[Jersey Bill]

The vertical rise of the flue makes a difference also. The higher, the better.

 

[barneshilary]

Thanks for the info. I checked the manual and it said it should be 7". Will that inch make that much deference?

 

[Nofossil]

Thanks for the info. I checked the manual and it said it should be 7". Will that inch make that much deference?

Like many things, it depends. If your boiler depends on the chimney draft for combustion, it might. A taller and better insulated chimney will tend to have more draft, so you might get by. The difference in cross sectional area is more than you think - 7" is more than 35% larger than 6" in terms of area. If it's a really large boiler, the cross sectional area might matter more, because the flow velocities will be higher.

If you went with the 6", what would it take to upgrade after the fact if it turned out that is wasn't enough? That's the risk, I think.

 

[barneshilary]

Thanks for all the input. Basically what I am trying to do is keep the cost down and still have a good system that works well!