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Batch box RMH insode a Jotul 118  RSS feed

Posts: 2
Location: Lyme, New Hampshire
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I was lucky enough to score a Jotul 118 for free locally a couple of months ago. Instead of repairing the cracks in the stove, I decided to make a rocket mass heater out of the stove. I have seen this video from Ernie Wisner about such a combination:

In contrast to the design in the video above, I have insulated the firebox and heat riser with insulating firebrick (IFB 2600) from Ceramaterials. As can be seen in the pictures below, I still need to put bricks over the top and make the riser out of stacked bricks.

This stove takes inspiration from Peter's design:

The dimensions are box W8"xH9"xD15", port W3"xH9"xD3", HeatRiser L40.5"x6" (and see pictures below). I am hoping this insulated hybrid design will burn cleanly. I still have to decide how to get a P-channel incorporated into the design.

One main question I have is with regard to extracting heat from the stove. Typically, the mass part of a rocket mass heater is a cob bench or something similar. The hot gases pass through a snaking horizontal chimney and heat up the cob/mass on its way through. In this set up, the mass is at room temperature or warmer as it heats up, so the gases provide heat to the mass due to the temperature difference (Tgas-Tbench). However, I am looking to avoid such a large bulky bench. If I put a few barrels stacked on top (20' ceiling) and a regular 6 inch chimney on the side, similar to this setup:
then put fans behind the barrels/chimney throughout the burn time, would the heat transfer be similar? In this case, the heat transfer would occur over a similar surface area, but the heat transfer would be a function of temperature difference between the gases and the air itself (Tgas-Tair). I have about 600 cubic meters of air in my house which weighs around 720kg. Can I get a good enough heat transfer with fans so I can use the mass of the air in the house as the thermal storage medium instead of a cob bench? The house has a fairly tight envelope.
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Overall stove.
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From the front
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From the top.
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Directly overhead.
Posts: 2580
Location: Upstate NY, zone 5
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Good looking project! It will be interesting to see how well it works.

Have you studied the information at batchrocket.eu? According to the table there, the port for a 6" system should be 2 3/16" wide x 9 1/2" high, so yours is a bit oversize and may not develop proper turbulence. I might slide the port sides together a bit to make it 2 1/4" wide instead of 3".

You could use the stacked barrels for heat transfer surface, but this would give only an instant heating capacity, with no real stored heat. Air is not a very good heat storage medium. You would probably get much better results with a vertical masonry bell, which would take minimal floor space, be as tall as you want, and hold and radiate heat for numerous hours after the fire is out. You do need a strong floor to support the concentrated weight of the masonry bell.
Ben Barrowes
Posts: 2
Location: Lyme, New Hampshire
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My batch box rocket mass heater has progressed to the point that I hope to install it in time for our New Hampshire winter in a couple of months.

Below is what the stove now looks like without the barrels on the top and to the side which will serve as radiating bells and mass with rocks in the side barrel. Insulating firebrick lines both the firebox inside the stove, bottom top and sides, and forms the vertical 36" riser section just by dry placing them there. In fact, I do not plan to use mortar in this stove at all so that I can easily disassemble it in the future.

I put 8 to 10 two inch thick 14 inch long pine sticks as fuel for the initial burn. The current air intake is on the bottom of the stove and comes up through the fuel past a quarter inch stainless steel screen that the wood sits on. The plan is for this external air intake to go through the house floor drawing air from the outside. There is also an air channel in the bottom of the Jotul stove that allows air to travel under the bottom layer of bricks to a secondary port at the beginning of the heat riser at the bottom.

I started the fire with this little electric firestarter which only took about one minute to blow hot air through the system to get the draft going, then light the pine on fire, then fan the flames so that everything gets going:
Here’s a video of the initial burn. No smoke after the first 20 or 30 seconds, and I was amazed with the insulating firebrick that the metal of the stove itself did not get warm for the first 5 to 10 minutes of the burn even though I was getting the rocket effect up through the riser. The insulating firebrick lining the firebox really did its job. The fire burned hot and violent for about 25 minutes, then the pine sticks had collapsed somewhat to about half their initial height whereupon there still was no smoke, but there weren’t flames in the riser much either. If I threw another stick on, it would immediately burst into violent flame again in the rocket effect could be heard. After the 25 minutes of rocket style burning, the sticks kept putting out decent heat for about 15 minutes, then there was smoldering for another 30 minutes or so until there were just a few coals and a bit of ashes left. During the 15 minute section there was a little bit of black smoke compared to no smoke during the 25 minutes.

I put a stainless steel quarter inch mesh screen both to protect this soft insulating firebrick lining the firebox into help the wood not block the 3” diameter air intake port at the bottom middle of the firebox. This seemed to work well to provide plenty of oxygen both at the main port and that the auxiliary port at the beginning of the heat riser.

The plan is for this to become a two barrel system similar to the Dragon Heater derrick build kit using barrels:
I bought the curved collars from a Vogelzang-type double barrel stove kit to attach some 6 inch black stovepipe between the barrels and from the second barrel out to the chimney. I have some ceramic wool to form gaskets at junctions between collars and barrels. Here’s a picture of what the end system will look like, again with 1000 pound of 6 to 12 inch diameter rocks filling up the bottom side barrel.
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Current batch box heater without barrels
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air distribution system
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eventual double bell mass system
See ya later boys, I think I'm in love. Oh wait, she's just a tiny ad:
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