Seth Hofstetter

Allen,

Thank you for the input! I am working from a hard copy, first edition (I believe) of the book I bought at a garage sale some time ago. Is there alot of additional material in the third edition?

Has anyone ever tried lining the hot spots on a riser made of steel with fire brick or perlite/clay cob? To my understanding, the hottest point for the riser is where the "jet" slams into the side wall after the burn tunnel. I assume, from your response, that most attempts at these result in the steel slowly eroding and combusting from the heat and temperature change. I think I will just build the fuel chamber from steel, and then fire brick for the burn tunnel and riser...pretty much following the books design layout.

Thank you, as well, for the information on the exhaust tube. I suppose it stands to reason that one of two exhausts would exhibit less resistance to the air movement. I will attempt to make the ductwork with cobb and a PVC pipe which will pull out once the adobe dries.

Also, I'm thinking of welding on fins to the side of the heat exchange barrel to act as a heat sink and hopefully help disperse more heat into the room, possibly cooling off gasses inside a little faster...my only concern is losing some of the clean combustion if the gasses move out of the barrel too fast.

I'm fairly new to the rocket mass heat concept, but I have worked with potbelly stoves before and I have a small coal forge, and have had a few years of work as a mason. I am currently in the planning process of building a small, primarily adobe, RMH in my tiny greenhouse. I intend to use a U-shaped thermal mass running along the sides of my greenhouse. I was wondering if anyone had successfully split the exhaust line and run it through two separate thermal masses, then back towards each other to come out through one point. I just watched a video where one had failed due to the 4 inch line used in the thermal mass, but I wondered if such line could be reduced and split from 8 inch and still function correctly.

What I gather in my own research into how these function, after the combustion chamber the name of the game is air volume (CSA, cross sectional area I believe it was referred to)...too big and the air doesn't flow fast enough resulting in ash particle build up, to small and not enough volume can be moved resulting in back draft or similar effect. Is there an optimal length for the duct running through the thermal mass? Also, is it preferable to vent the exhaust vertically or horizontally?

My plan is to use structural steel (have some tubing and C channel laying around) for the fuel tube leading up to the combustion chamber. A riser built from fire brick and topped with flue liner, a 15 gallon drum (also laying around), and adobe brick for the vent through the thermal mass (likely I'll use stovepipe for anything in livable structure, but I think it should work for the greenhouse build). The thermal mass will be made of adobe and pea gravel/sand mixture (creek rock and sand collected locally).

I'll post photos of the build once I've settled on a method for my madness, updates as the project is progresses, as well as a follow up to show what it does next winter. The goal here is to grow my seedlings in late January/February in Zone 5. Most winters here in Central Missouri are fairly cold, but recent patterns make already unpredictable Missouri weather even more elusive. If it works, I will be building one or two in my home for supplemental heat (and so my wife, who freezes every winter in this turn of the century house, will have a warm spot to sit).