Feedback regarding construction (materials and fitting):
Bricks: No visible damage on bricks. Large clay joints show some cracks but slim ones remain tight.
Steel: No visible damage on the floor channel steel. Even the stub near the port is in good shape. The door looks good too. No wrapping.
Glass: The firebox window remains quite clear after a full winter season. The primary air is flowing through two slots on each side of the door frame. They are quite efficient to avoid deposit on almost the whole surface of the window.
Measurements: three thermocouples and one amplifier are out of order, more than 50 still working well.
Construction improvements for the next design:
- Clearance between the bottom slanted bricks and the floor channel needs to be wider. I had to dismantle some bricks to remove the floor channel. It fills up with ashes as well as the heat riser bottom and the port.
- There were still some linseed oil in excess on the door when mounted. Ugly drops solidified during the first runs. I will wipe it more cautiously next time.
- TC redundancy: systematically put two TCs at the same location. Once in place, they cannot be replaced in case they break or age.
Feedback regarding fire quality and efficiency:Thanks to this new stove, I did not have to buy any wood this winter. I loaded it with any type of waste wood (untreated) which was lying for years around the house. I burn quite efficiently a lot of cedar cut two years ago. This prototype cost me as much as I usually spend for fuel wood for one winter.
Lighting:
- starting from cold stove: 700°C inside the heat riser can be reached within less than 10 mn by lighting first a small fire in front of the port with very thin wood, carton and paper.
The full load of wood (~ 3kg) is put in front of the burning flames.
The door is left slightly open until 500°C is reached in the heat riser.
- Refueling on glowing ember: this stove being under scaled, up to 5 runs a day are necessary (and not sufficient). Putting wood on glowing ember leads to thermal overdrive, i.e. pollution, dark fumes and lower efficiency. I had to wait until almost all ember was consumed. The remaining glowing ember is pushed toward the rear near the port. A first layer of wood is then put in front of the ember. The rest of the load is put when the first layer started to burn. Usually, the door can be closed immediately.
- Bypass: lighting with cold bells is possible but it takes more time to get a nice fire with clear exhaust. Opening the bypass of the second bell helps to get it faster. With warm bells the bypass is not needed
Fire quality (pollution, soot): - Ideal run: most of the time, the wood will burn from rear (port) to front (door) quite nicely and heat riser temperatures remain stable between 650 and 750 °C for almost an hour and then decrease slowly.
- Thermal overdrive: When the burn gets too vigorous, it produces dirty smokes. It often comes from wood load type and stacking. Most of the time, I manage to stop the thermal overdrive and get clean smokes by packing the burning logs with a shovel until the pile is almost air tight.
- Stacking: In order to get a nice fire burning slowly and clean, I noticed that it is better to put larger logs at the bottom of the pile and thinner ones on top. Since the latter burn faster, putting them bellow bigger logs brings the whole load to burn at once with lots of black smoke (thermal overdrive).
- Stacking (bis): The former process has also a drawback. Bottom bigger logs are lying on ashes and will consume slowly at the end of the run. It is a source of pollution. Lying them on perpendicular short pieces of wood allows air to flow underneath the wood pile and nicer combustion at the end of the run (I read lately that Peterberg is doing it with metal bars instead of pieces of wood).
- Refueling: I noticed that if the firebox temperature is too high before lighting (above 200°C) and/or the wood logs too thin, thermal overdrive will take over. It happens more often with pine than hardwood.
- Soot: After one season burning essentially cedar, up to five burns a day, the first bell is quite full of soot. The black oven window is totally black.
Heating power:
- Scaling: This stove is a trial on the existing flue pipes (125mm 5”). It is clearly under scaled to heat my whole house (two stories, ~120 m², with low insulation, no door between the kitchen and the stairway). The final stove will have to use larger flue. Nevertheless, 125mm flue was sufficient to get comfortable in the kitchen (heated room) as long as outside temperature was above 10°C during the day and just freezing at night. One to three fires a day (less than 10kg wood) was enough during more than half of the heating season. But I could not burn more than 5 fires a day without creating thermal overdrive (the firebox needs time to cool down between two loads). When it got colder, kitchen temperature fell down to 13°C, less than 10°C for the rest of the house. Since I want to heat an area about three times bigger, I guess the flue CSA must be around three times bigger. Therefore, the flue has to be between 200 and 250 mm (8 or 10”). It represents loads of 14 to 27kg. With my former stove (a traditional low efficiency one) I used to burn 30kg on coldest days and get my kitchen above 22°C and the room besides with the small bell around 16°C. So my guess is that a 200mm (8”) batch should be sufficient. If it gets really cold I will burn three loads a day.
- Door window orientation: Presently, the stove door is facing a wall, i.e. we do not see it from inside the room. I noticed that the fire does radiate quite a lot through the door window. Besides, having a look at the flames is quite relaxing. Therefore, the stove door will face the middle of the kitchen in the next design. I may also replace the oven window with a metal sheet which will radiate heat faster than the brick skins.
- Chimney damper: I read from Peterberg that at the beginning of coaling phase, air inlet should be closed and chimney damper left open. I wonder when one should close the damper and if a damper is really necessary. (?)
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