8" and 6" flue Pipe Together

I got the pdf file of the RMH but it does not cover this problem it may not be a problem well here goes my RMH is going to have a bench on the L side which is 7' across and 6' out my vent is going to be 8" with 26' long 3 90, 2 co tees and a 45 to the vertical pipe on the other side of heater I have a 3 to 4' bench my question is can I use a 6" system on the short side and use a 8x8x6 tee to tie the 2 vents together and go out with a 8" I am worried about the pressure between the 6 & 8 in pipe and not getting a good draft or pull? I was reading a post b4 mine and the ONLY fire brick I can get in my neck of the woods in AZ N/W side next to that beautiful and massive grand ditch is the heavy ones at Home Depot one more thing finding clay dirt around here is like finding a penny on the white house lawn, lots of sand around here TIA David

David Marin : I am afraid a redesign is in your future, If I understand correctly you intended to have Two horizontal chimneys of different lengths and diameters?

An RMH with two identical horizontal chimneys is a very complicated build attempt for a master of Hundreds of Builds, generally one of the two pipes becomes
dominant and the other one is an anemic thing that could not blow out a match or warm a fur muff !

In this case the warning came in time! You are now dependent on your local economy and not a big box store with a headquarters 10 states away ! You will have
to Try your local 'Yellow pages' look under

Potters ceramists

pottery supplies

ceramic supplies,

you can also ask a high school Art Teacher or play phone tag with a member of a College Art Department !

These people can if charmed enough, lead you to good local clay, or you may have to talk to the local town, county or state highway departments, they will know
where a hill side cut becomes water soaked in a storm and landslides down onto the road,=> Clay!

A local excavation contractor will have a good memory of where he has found clay in the past, a case of old farthing slosh is payment in full !
hope this helps as usual all questions and comments are solicited and welcome ! Big AL !

Ck the YP's 4 "brick". ACME brick is local here and has all kinds of bricks. The light weight ones are $1.06 4 half thick and 1.29 for full.
Or ck with a masonry contractor.

I think it is possible to integrate different size ducts in the exhaust, but some serious calculations and observational data analysis would be in order.
The use of a diverter valve/flue damper might be one way to balance the flow. Placement would be key.
It's times like these that I wish I could talk to my Uncle who was a fluid mechanics engineer and designed fluid and air circulation systems. He is now a physicist and computer science chair at UA in Anchorage working on quantum computers. I guess there are a few genius genes floating around my family:)

p.s. David, love your sig quote, one of my favs

Do folks think that going from an 8" exhaust flue in the mass/bench to a 6" vertical outlet flue through the roof would work?
I already have 6" vent pipe through the roof (double wall stainless/expensive) that I'd sure like to us.
Something mathematical in me is saying that if the whole flow has to stop down to 6", why do 8" at all anywhere in the system? Though, the air would essentially move slower through the 8", then pick up velocity as it moves into the 6" - doesn't seem to be a bad thing. It certainly would restrict flow a little though...

Thoughts?
Thanks,
Ben

Ben Falk : I can strongly recommend you to go to> rocketstoves.com to Doownload your PDF Copy $15 of Rocket Mass Heaters, With ~100.000~ Built world wide,
most of them have been made following 'The Book', and 95% of all the first time RMHs (that Worked ) were made following the book!

To answer your question, for all first time builds, your best plan is to stick to the more conservative practices that have already worked, a pure 6'' system, if big
enough for your needs, will give you great service over a very long time, I would rather talk to a man who had built one RMH, and lived with it for ten years, then to
talk to the guy who had 10 different iterations, and had mixed results ! After you get your First one working well, is soon enuf to sit with a blank piece of paper and
plan your next one Hope this helps and is timely, As always, all questions, comments are Solicited and Welcome For the Craft1 PYRO - Logically big Al !

Thanks Al..
I bought the book the other day and read much of it... Seems like 8" is well proven but gives bigger capacity...

Do folks think that going from an 8" exhaust flue in the mass/bench to a 6" vertical outlet flue through the roof would work?

Unfortunately, no this wouldn't work. We have tried it and in order to get the fire burning properly, we had to close off part of the feed tube. This, of course, defeats the purpose of the 8" system.

With an 8" exhaust flue, an 8" system does work really well. We have done 2 different style builds with the 8"... a castle with a bench from chimney flue liners and a green house heater which involves steel drums lined with dense fireclay bricks for heat storage. Both of them work great, they draw well and store a lot of heat.

See the blog at the address in my signature.

C.S. i added a little on to my last post, it was the 1st Video "Chelles Rocket'' I wanted you to see a pretty conventional build ! Good Night ! A.L.