kelly myer

Thanks Mark, I will check it out.

New Project - unless it is covered somewhere else on Permies!!

I am working on designing (building soon) a RMH totally enclosed within a 55 gallon drum. J-tube at the bottom, insulated riser in the back. Then the heated gasses do a 180 back down into the drum - making a 90 just above the burn chamber and across the lower 1/3 of the barrel to another 90 degree turn then out the top. All these three runs within the barrel will be surrounded by mass for radiant heat. The top would have a heavy 1/4" plate welded on for cooking or a cast griddle sitting on top. To preserve heat when not cooking a round 2" piece of soap stone or other mass would be placed over the cook surface.
Question: Would a 4" j-tube generate enough heat to "fill" this mass or should it be a 5" j-tube and insulated riser?
I'm guessing a 6" would be difficult to fit inside the barrels space and make all the turns needed.

Secondary idea - rocket stove in a bottom 55 gal barrel with a 2nd 55 gal drum on top that is insulated as a bell. A 30 gallon stainless barrel enclosed in the top barrel as a water heater with three or four hollow stainless 3" tubes welded into the bottom of the stainless 30 gal drum for more surface area to heat the water. So this 30 gal stainless tank will likely be a 25 gallon water heater after accounting for the inner heat exchanger tubes.
This stove could be a 6" box and riser or a small batch box and 6" riser to generate the heat and duration of heat needed to heat 25 gallons of water.

This idea is born from the following requirements:
* Compact design for a small space, but still has some mass to it for extended warmth (fire once or twice a day)
* A gravity fed rain water catchment system will feed the water heater design
* No pumps used - this kind of excludes using coiled pipes that circulate into a holding tank - the holding tank is the heater in this design

For a true bell you will want to move your exhaust down to the side about 1/4 or 1/3 from the bottom, but above the top of the fire box. Then the super heated gases will stay in the top of the upper barrel while the relatively cooler gasses escape out the side near the bottom.

Graham,

I've thought about doing a mass wall or pony wall shared with multiple rooms. That could also be a masonry wall built as a bell. This might be an easier solution just considering the maintenance of an under floor bell. The bell could also be dangerous as the bell itself would be a potential risk for asphyxiation!! Very little or no oxygen would be down there. Any maintenance plan would involve venting the bell before doing anything down there.

The idea of a bell is just a mass heat sink with an inner open cavity for the air to stratify within. Hot air rises to the top and heats the mass, cold air drops to the bottom where you would exhaust out of the bell.

In the more common series of flue pipes in a traditional RMH setup the stove is always pushing all the air out and hoping most of the heat is absorbed by the mass before the air exits. The exhaust temp would be an indicator that the mass is "heated" and also indicate how much heat is being lost to atmosphere. The mass is hottest near the stove and cooler as the air moves along the duct. In a bell only the coolest air is exhausted out of the system - at the bottom -  and when the fire is out the hot air stays in the bell until the whole system cools. This should make it more efficient. In addition, if the hot air can be introduced into the bell in a distributed manner, rather then one large dump of air in one spot (like RMH's), the top of the bell would tend to heat evenly instead of having hot spots. If the top of the bell is your floor it should be an evenly heated surface and comfortable if you don't fire the stove too long. Would have to experiment with firing time to find the sweet spot for the mass that is incorporated.

The idea of pex in the mass to store and then distribute heat is an excellent idea, would also have to consider the cost of filling the system with antifreeze and keep it filled so air in pipes is not an issue. And I was looking at solutions without too many controls aside from the burn in the stove. The cabin this will be in is an open concept design so am hoping heat distribution won't be an issue. Especially if the bell spans across the few walls that will be in the structure.

Thanks for the replies and feedback.

Graham - regarding the chimney - the drawing was a quick sketch not to scale and just to relay the concept. The outer chimney will be above the stove. I was also trying to show some loops in the design to create "cold traps" so air would tend not to backflow through the system when cold. Also looked at another interesting design called the Ondol - Korean floor heating. Lots of stuff that our cultures have left to the past because of fossil fuel and electric use.


John - Yes, I will incorporate a small burn chamber in the chimney to start the draw, similar to the burn box in a Russian masonry heater. Or might even use a small air pump just to get things moving, it will be quite cool on the chimney side. It would follow the principle of "objects in motion tend to stay in motion". As soon as the entire system is "flowing" in the right direction (air in the system is in motion) the fire can be started. Then the rocket effect takes over and keeps things moving in the right direction, ie out of the house!!

To Michael:
The metal box would be supported under the top with metal beams, small open spans in the middle of the beams supported across by posts all under and inside the box. The box would be welded on top of and around the beams. The thin cement floor on top (4"?) would be rebar reinforced. Air would be able to move freely throughout the entire upper part of the box and around the beams inside.

To Graham:
Looking at pics of the Roman Hypocaust - yes similar but using 1/8" metal for the box and sections of beams to span across the posts and support the inside of the box at the top.

To Eric:
A concrete slab with ducting large enough to provide flow might work, but thinking it would be pretty thick. And floor would have hot spots where the ducting is thinnest at the rounded top. This would probably be the easiest to do. Maybe use square ducting, steel reinforced cement between to act like beams and then flooring across the beam structure. Square beams would act like long mini bells within the floor and high density foam under the whole thing for insulation. Likely be limited to 6" square ducting and not too wide so flooring doesn't buckle or collapse. Maybe the "Bell Structure" could just be a layer of cinder blocks sitting on their side to provide ducting but thinking this would also have a hot spot where the RMH exhaust enters.

I've been looking around for information on RM Heaters that would feed in-floor heat directly. The idea here is a bit different then using water in tubes. Watching many RMH vids and also the idea of a Bell style heater on a RMH stove gave me the idea of creating a bell in the floor of a cabin or house to provide in floor heat.

In my thinking the design would use the floor as the mass. The house structure would have to incorporate a shallow metal box sufficiently supported to be the floor and support 4"-5" of mass as the heat sink. This heat sink could be a concrete slab finished with floor tile inside. The metal box would be a 12' X 20' X 3' BELL, which would be most of the floor in the house. The down feed from the RMH would be ducted (insulated ducting) to the center of the floor box bell to heat the mass, which is also the floor inside the house. Only the sides and maybe the bottom of the metal box would be insulated with standard insulation or air crete (foam and concrete mix) to hold the heat so it would warm up the floor. Exhaust the cooler air at the bottom of the box. The RMH would be built with a damper to this "under floor" space so it could be sealed off when the burn is finished. Thus preventing back draft of the hot air back into the home. The design could also incorporate a below the bell air trap to help prevent hot air from back feeding into the home.

Anyone tried this yet? My idea was inspired by the Walker Stove Bell Bench design.