Design Principles of Secondary Burn tubes?

[Nonprophet]

Does anyone know of a publication, owner's manual, video, etc that gives some of the basic design principles of the secondary burn tube systems? Diagrams, drawing, videos, and other visual aides would be best.

I have an older non-EPA woodstove that I'd like to modify by adding burn tubes to it. So basic concepts like tube diameter, how big to drill the air inlet holes, and what distance should the pre-heated air travel prior to ignition would be very helpful information.

Thanks!


NP

 

[Pagey]

Lopi cutaway

http://www.lopistoves.com/how_it_works/wood/

 

[EddyKilowatt]

I've considered a secondary retrofit myself and have spent some time researching and thinking about it, but have never come across anything like a textbook or tutorial that gives any general treatment regarding placement, flow rate, temperatures, etc. I reckon the knowledge is pretty much confined to the R&D departments at the stove manufacturers. But there are a few clues here and there.

Here's a thread from 2008 with some posts from a fellow who did a secondary burn retrofit. I think if you search here at Hearth.com you may find one or two others who have also.

https://www.hearth.com/talk/threads/17993/


Manufacturer websites have some info along the lines of what Pagey already posted... if you look around in their 'Support' area you can usually download manuals which usually have exploded parts diagrams that you can study. Kind of slow going and can be tricky to figure out airflow paths, but interesting none-the-less.

Finally, there's nothing like spending an idle afternoon in a well-stocked stove store looking at, in, under, and behind every stove in the place. Politely, of course! But you'll come away with a decent feel for how different manufacturers approach the problem.

Finally, I think you just have to give it a whirl. Start with cheap tubing and small holes and be prepared to try a few -- or several -- different hole sizes, placements, diameters, etc. Invest in an IR thermometer, pyrometer, and a couple of thermocouples so you can quantify what you are doing.

Eddy

 

[mellow]

This is also another really good thread on secondary burn retrofits:

https://www.hearth.com/talk/threads/31420/

 

[SmokingAndPoking]

.75" or .875" OD tubing

5/32" - 7/32" holes


Spacing, amount of air let in, angles, etc are all subject to a lot of trial and error.