Aki Japan Masonry Heater

Nagano, Japan: Stucco Contraflow Masonry Stove

Fire Works Masonry’s latest job was an outstanding opportunity to build a masonry stove for our friend and Masonry Heater Association colleague Aki Yoshimizu in his lake cottage in Nagano, Japan. Aki is a builder in Japan and is the owner of Peak Home Builders. The photo below shows the functioning, almost complete heater.

The heater was designed by and built with MHA founding member Norbert Senf of Masonry Stove Builders from Quebec, Canada. Norbert also posted a detailed photo report of the entire project on the MHA News E-zine.

The energy efficient fireplace is a Finnish contraflow core based on the Masonry Heater Association’s Heater Plan Portfolio. The fireplace is faced with dense brick pavers. The rough stucco coat will be finished in a local Japanese clay plaster. The photo below shows the first small curing fire burning in the firebox.

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The lakeside cottage is located in a beautiful rural setting. Like many homes in Japan, the home is not well insulated and can be a challenge to heat in the winter. The mountainous area regularly gets heavy snow falls and temperatures as low as 0F. Aki became interested in the possibilities to heat efficiently and cleanly with locally available firewood.

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The photo below shows the great view of the quiet lake from our workroom door.

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The heater starts with the layout. The masonry stove will have a very unique heat exchanger design for the upper bedrooms designed by Norbert.

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Once we establish the layout, the base courses of the fireplace begin. The photo below shows a new layout design for the contraflow base designed by MHA member Eric Moshier.

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Aki hosted the build as a workshop and several interested and adept volunteers attended. The photo below shows Norbert Senf, Mamoro Ooishi, Yuuichi Kada, and Takeo Onozawa.
Mamoro is a chimney sweep and woodstove salesman from Hokkaidou. Yuuichi is a mason and garden craftsworker
from Aichi, about four hours away, and Takeo (Ono) is a chimney sweep from Nagano. They met while doing volunteer
work after the Tsunami.

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With so many helping hands, the build goes quickly.  The photo below shows the completed firebox and the start of the throat behind the white oven.

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The white oven slabs are installed. Aki is a carpenter and builder. He made excellent forms and castings for the high temperature concrete slabs.

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The final courses and secondary combustion chamber are completed above the bake-oven.

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The two side downdraft channels can be built next.

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Once the side channels are complete the crew installs the heavy high temperature capping slabs.

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With the core completed, the crew enjoyed a great evening campfire and cookout.

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The masonry stove work begins again the next morning. Locally available dense, red brick pavers will face the core.

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The bricks are delivered to the jobsite. The local hardware store allows customers to borrow this small pickup for 90 minutes with no charge. These useful small pick-up trucks are everywhere in Japan. The truck gets about 50mpg, carries over 700lbs and costs under $9,000.

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The photo below shows the start of the face brick, chimney connection, and small heated bench.

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The heater installation is in a seismic zone. Threaded rods are drilled and epoxied into the base concrete slab. The rods will be buried in the mortar slush between the core and facing. A steel plate on top of the heater will bond the masonry and rods together.

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The brick facing is about halfway complete after a long day. The jack arch spanning the door openings is the next step.

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Norbert inserts the keystone into the jack-arch. The jack-arch is left proud from the brick facing for a design element.

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The brick facing progresses. The photo below shows the closing keystone for the second jack-arch above the bake-oven door.

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Norbert’s heater design also includes a unique curved brick wall surrounding the chimney connection. The curved section is seen in the photo below.

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The final brick courses are nearly complete in the photo below. One of the threaded rods for the seismic reinforcing can be seen above the brick to the right.

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With the brickwork completed, the stucco plaster coat begins. Aki looks admiringly at the brick face while he holds a fiberglass mesh in place to reinforce the plaster facing.

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Later that evening the crew burns the first small curing fire around the completed rough coat heater.

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With the rough plaster coat completed, the doors are installed into the brick facing.

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The photo below shows the nearly completed, clean burning, energy efficient fireplace with another small curing fire. The heater still needs the final plate for the seismic reinforcement, a small top for the heated bench, and a final decorative plaster coating. Aki will most likely use a local, traditional clay or lime plaster.

Japan Masonry Stove Complete Facing 0922b


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