couple of questions

i see talk of risers being too short. can a riser be too tall? when (if) and why does it hamper the performance?

also can the space in the barrel be really big? like 6" on all sides? if there is a lot of open barrel space does that mandate a larger pipe in the mass? as to not choke it down after opening it up in the barrel.


can the riser be offset inside the barrel, with no ill affects?


wow, learning about these stoves is an addiction! lol

Ronald, i've never heard of a heat riser being too tall. Tho there's practical limits. Like heat transfer to the walls of the heat riser. But we're talking about tenths of yards

If barrel has a big gap, it's called a bell and sometimes you can completely skip the pipe in the mass. Here's one thing which can be done. http://s65.photobucket.com/user/mremine/library/NYC%20Rocket%20Stove%20Build/

And yes, a heat riser can be ofset in the barrel.

Ronald Bush : The top of the barrel is the 1st heat energy radiating surface, and is valuable as an secondary cooking surface, a very high heat riser would require
a barrel on top of another 1/2 or Full barrel, this Moves that radiating surface very close to the ceiling, not handy for cooking and radiating heat to the ceiling rather
than where you would traditionally want it !

In an effort to promote the Temperature differences between the Ascending Gas stream within the center column of the Heat Riser, and the temperature of the
Descending Gas stream between the Heat Riser and the Barrel, the Heat Riser is commonly wrapped with additional High Temp insulation ! As a 2'' gap around the
barrel is plenty this allows us the use of 'Rockwool type thick insulation'.

Ceramic blanket insulation which insulates as well with less thickness can be used in this location but this material is very pricey !

The barrel can be cautiously off-set, with a 1.5 '' gap between the Top of the Heat Riser and the Barrel for a 6'' system (2'' for an 8'' system) you will create a hot
side and a cold side, this can allow a closer installation to an adjacent interior wall, and more heat radiated into the heated space, narrow side cool wide side hotter!

Some people are reporting a reversal of hot and cold sides whit the gaps, especially the Top of the Heat Riser to Barrel gap bigger than 2''.

This information is all to be found in the brand new 3rd edition Of Ianto Evans' Great Book " Rocket Mass Heaters ''! For the Crafts Big Al

ronald bush wrote:i see talk of risers being too short. can a riser be too tall? when (if) and why does it hamper the performance?

also can the space in the barrel be really big? like 6" on all sides? if there is a lot of open barrel space does that mandate a larger pipe in the mass? as to not choke it down after opening it up in the barrel.


can the riser be offset inside the barrel, with no ill affects?


wow, learning about these stoves is an addiction! lol

In the PDF: www.aprovecho.org/lab/rad/rl/stove-design/doc/18/raw they discuss a heater with a tall internal chimney and how they prevent the fire 'being pulled off the fuel'. I'd have to see it myself.