Feed/Burn/Riser ratio

This ratio will change if you add additional air intake, either lower than the Feed, or forward of the Burn before the riser. Correct?

If you are talking about cross sectional area ratios, you would want to maintain the same totals throughout; but there is no proven good reason to add air intake anywhere but the feed tube and a P-channel which sits in the feed as a discrete part of it. One researcher (Peter van den Berg)
tried all versions he could think of over a couple of years intensive work, and found that the standard system works best, with the insertion of a P-channel which you can read all about by searching for it.

Glen,

Thanks a lot. I hadn't even started thinking about batch boxes yet. Next you'll have me growin stuff. lol
Actually,  my feed tube question, is better explained with another sketch.

If secondary air channel vents/ports were added, wouldn't the feed tube height be able to extend past the ratio formula?
Allowing for extended lengths for alternating fuel sources.

Again thanks for your input, I love to learn.

Scott

The feed tube needs to have all of the air coming down from its top, to keep smoke and flames from traveling back up and out to the room. Side air inlets would defeat this feature and cause you major problems. So the 1:2:4 or 1:1.5:3 length ratios are really what they sound like.