The heated bench - all and everything about cross sections.

Dear all.

If the outside chimney has 20 cm diameter - and the built in chimney (and burn tunnel) has a 20 cm diameter as well - what effects will  areas in the exhaust system with a larger cross section have?

 

Hello Øystein,

could you give us some more details on your stove?
Are you planning one or is it already built?

A little sketch or a photo would also be very helpful.

In general a larger cross section means that the flow of gases slows down.
If you make the diameter much bigger you end up with a bell or stratification chamber where the gases stratify (hot gas on top, coldest on the bottom). I think that happens with  >3 *CSA.
Did you try searching for the juice straw exhaust in the forum?

Another thing you should keep in mind is not to build heat traps, that is to say that the exhaust pipe should be level or slightly rising, not going up and down.

Benjamin Dinkel wrote:Hello Øystein,

could you give us some more details on your .

Thank you! - So, basically, I ask because I am contemplating 3 spaces with a larger cross section. One is on the outside part of the construction (pictures). I am making a rather big fireplace at the base of what will be the chimney- and the exhaust will come out horizontally from the wall, and connect to the rather big oven. — The more heat I can store on the inside of the house the better - in a prototype I made the bench hardly warmed up at all..  

The three different sections of the construction. I’m not at all sure about the bench part though - I want as much heat as possible to be stored there - since the core will be covered by stones I’m not worried about that part getting hot, but I feel the air will not have sufficient time in the bench, and think about creating more surface using smaller pipes - but I also want to make sure that it has a steady draft.

Here is a link to another topic I created for the construction of the core - https://permies.com/t/256987/Feeder-tunnel-riser-dimensions#2483428