The book is fairly generic when it comes to sizing.

Basic drafting principles are stated, but not math involved.

I get the basic's and this is not my first, just my first 'big' one.

I understand that this is still small to you all, but not to me.

I require 4k Btu's, in hopefully under 2 hrs.

Not certain if possible.

I have never gone this big..

Math and past experiments say possible..

Including thermal losses and transference of heat to the tub (though I'm known to screw up the math at times..)

In my smaller versions I have eliminated the tunnel.

Book speaks of keeping it as short as possible, but how do you all feel about not having it?

Keeping the

feed tube smaller than the draft tube is basic drafting.

Has anyone come up any mathematical ratio's to improve efficiency?

Then comes the basic question...

Btu's achieved from a 6", 8", 10" riser???

Then we go back to an original..

6" feed, use ?" rounds

8" feed, larger rounds??

Are you folks actually at using a couple 3-4" rounds vs. using many 1-2" rounds (or splits)?