Glenn Herbert

I store my firewood around/behind the bell of my RMH, and if I put up wet half-green wood in autumn it is bone dry by midwinter. Also significantly lighter. The bell surface where the wood is never gets too hot to touch.

All wood combustion will have water in the exhaust; the products of complete combustion are mostly carbon dioxide and water.

You can build a sidewinder with the port and riser on one side of the firebox, if you are not restricted on bell width.

My 8" J-tube is 24" long from front of feed to back of riser mounting. The burn tunnel ceiling is about 8-9" long. It works excellently, leaves nothing but fine gray ash in the floor, and in two cleanings of the bell in 8 years, has had maybe a few gallons total of fly ash settled on the bell floor.

If you can remove the barrel over the riser, your best bet is shortening the burn tunnel from that end, moving the riser closer to the front of the barrel.

Propping the water tank up away from the barrel top will greatly reduce the amount of heat that goes into the water. I would set the tank directly on the barrel top. The amount of water you describe will not boil dry quickly, but will heat much more quickly. Is the tank covered? Evaporation will release a lot of heat from the open top.

From your description, you did start with mostly instant radiation heating, only storing heat from the largely cooled gases. Therefore, you will not have much stored heat compared to instant room heating, so when you make the room comfortable, you don't have much for overnight. Cobbing the second barrel with say 4" would get you a much better balance between instant and delayed heating. It may be good to cob a good part of the first barrel too.

I would not have less than a 2" gap between riser and barrel; 3" would allow easier flow, and the only heating difference would be less concentration on the middle top and more on the sides and downstream. The fact that you are not getting a lot of heat in your first water tub is puzzling, assuming you get complete combustion and end up with only fly ash and no charcoal after a burn.

Best of fortune to you in building a J-tube system... as long as you follow published directions, it will be fairly quick, easy and effective.

I think it would be about as easy and definitely more effective to just build a modest J-tube system in your garage than to try to retrofit a bell onto your wood stove with the exhaust cooling and creosote generation that would entail. If you do a garage system first, you will be prepared to quickly do another inside your house with full confidence.

Heating rooms distant from the heater location could be tricky, and we can only advise usefully with a floor plan of some sort and/or good pictures.

I second Rico's comment about crawlspace access. Code even says that a masonry heater needs to be supported directly by masonry piers or foundation and not wood, so there is that to consider. Cutting out flooring to give easy access to build up from a crawlspace floor makes sense - you won't be wanting a wood floor under the heater in any case.

If the wall between rooms is load-bearing, you could get by with cutting a 20cm wide x say 30cm high slot near the base for the gases to flow from one side to the other, without any problems.

As Cristobal implies, the best setup would be a combustion core (J-tube or batch box) in one room, probably the lower one, inside a masonry bell of about half the size calculated for your heating load, leading through the wall to a similar bell on the other side, and then to the chimney. You can build the bells as three sided boxes with the existing wall making the fourth common side, to minimize space required. The core will require certain minimum horizontal dimensions inside the first bell, though part of the core can stick out if necessary. The second bell can be any shape that gives the right internal surface area, such as wide and flat to the wall, possibly projecting as little as 30cm.

Given appropriate planning, you can build an easy J-tube to start with and then convert to a batch box with very little waste when you have more time and experience. J-tubes do not require all of the wood to be split small; the bulk of your fuel after starting can be sized such that 3 or 4 logs will fill the feed tube.

You can use the slope to get some easy raised bed effect. Laying down logs parallel to the slope and filling behind them with topsoil can give nice deep soil on the upper side that is easy to reach from just below the log. It also avoids wasting new topsoil on the strip where you will be walking.

When I did this on a steep slope, I put in two or three logs with locust stakes to hold them, and turned up a strip of existing topsoil into the lowest part next to the logs, leaving a foot or so undisturbed to the next bed up for a walkway. This made for a uniformly deep planting area to fill with new topsoil. (My neighbor has horses on a small lot, and has for 30 or 40 years dumped their manure onto the edge of one of my fields, so I have a room's volume of composted horse manure to use for gardens.)