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Byron Campbell
Post     Subject: what is the max duct length on an 8" system?

8" system will drive about 50 feet of horizontal 8" round ducting in the thermal mass bench, minus about 5 feet for each 90 degree turn.

One option, to take all the guess work out of a first time RMH project, is by building according to proven tested designs. There are several nifty plans of various designs available here:

http://www.ernieanderica.info/shop
allen lumley
Post     Subject: what is the max duct length on an 8" system?

Philip Baldwin : It depends ! Even which way the wind is blowing on a given day can be a challenge!

Here is the best rule of thumb: 1st you build your system outdoors to prove it works, then you put your barrel on top and immediately come off of your manifold

with a final vertical chimney. This lets you prove that the Rocket base works and any future problems are in the horizontal plumbing or the final vertical chimney

Then you move everything inside and rebuild the Rocket Burner base and come off of your manifold with your horizontal chimney .

With a tall Heat Riser to push the hot exhaust gases and a well drawing Final Vertical Chimney you should easily get 50 feet of horizontal piping run through your

Thermal Mass Cob Bench. Remember to subtract 5 feet for every Horizontal Elbow and "T" with clean out . This distance should be long enough to get the measured

Temperature of the hot exhaust gases down to 120ºƒ to 150ºƒ which is more important than more length which may cool your exhaust too much and weaken your

draw .

As every single RMH is a one-off D.I.Y. creation that IS the best answer I can give you and the next guy after you ! For the Good of the Crafts ! Big AL

Late note did you ever give us a your location ? A.L.
Phillip Baldwin
Post     Subject: what is the max duct length on an 8" system?

I have Iantos book, however. I an having trouble locating the rules for maximum duct length on an 8" system.