I am not an RMH Doctor(But I did stay in a Holiday inn express last night) But what I think happens is that because the secondary burn chamber gets soo incredibly hot the ability for creosote build up is greatly reduced. Paul also expounds on that in the podcast. There are clean outs built into the system but because the burn is so full the ammount of ash is lessened also. I just saw a video of a lady's RMH and she shows how much ash she cleans out (at about 3:50) http://www.possible.org/a-look-at-chelle-lindahls-rocket-mass-heater/. Watch the whole video it explains how it works.whacker, great explanation.
Does a RMH need to have the exhaust cleaned more often? I thought that if the exhaust wasn't hot enough on exit, then there would be significantly more creosote build up?