what is the Max distance of 8" system exhaust

How long can I build my 8" exhaust for thermal mass and how do 90 degree elbows adversley affect that max distance?

An 8" diameter system is commonly recommended to be maximum 50' long of horizontal duct, minus 5' for each 90 degree bend. The bend up to the chimney is not counted here.

A warm HELLO to all folks at permies!
I've been studying the information about rocket stoves for three years now and I'm finally preparing for my own build here in the western side of Romania.

The following questions appeared: what is the Max distance of a 6" (15cm) system exhaust? (Ianto Evans and Leslie Jackson are mentioning a minimum of 6 meters of duct and 3 tons of mass heater for a 15 cm system). Should I cut 1.5m length (5 feet) for each 90 degrees elbow?

And can I run it horizontally for the first half of the total length and than in a vertical S shape towards the chimney? It will connect to an interior chimney about 7 meters high (of which 0.5m are above the roof edge). Chimney interior diameter is 15 cm, round shaped. Can I use black stove pipe for the duct in the bench? I will also attach a sketchup of my system as soon as possible. THANK YOU for helping a newbie!

I have seen maximum recommendations between 30' and 40' of horizontal duct for a 6" RMH. This thread has a post by Erica Wisner, one of the most experienced RMH builders in the world, with a number of considerations:
https://permies.com/t/29678/rocket-stoves/vertical-mass-heater#231730


A sloped/rising duct path could work, though you need to keep in mind the length reduction for bends. The black stovepipe should do fine.

Hey, thanks for pointing me exactly the information I was looking for! I'm thinking bells now always considered them a very smart option and a bell would definitely suit me better.