Personally I've never bothered but I guess you could wait until your stove is bone cold (like maybe in the summer), shovel what you can and then vacuum the rest?
Not sure, I've always run mine with some ash on the bottom to help retain a coal bed.
I honestly can't say how the system would run without any sort of ash bed.
Maybe someone else on this forum with the same stove has a different idea?
I think it is a Jotul thing as most other stoves have a firebrick lined bottom.....
I was doing it the same way, but over Thanksgiving I was talking to my brother (the engineer), and he said that the grooves allow the incoming air to wrap around to aid in best combustion toward the slow cigar burn. I pushed the ash toward the back exposing more of the grooves and it seemed to really get and keep the fire burning more efficiently. I was able to dial down both the air inlet and damper and maintained the same stack temperature as before when the air inlet and damper were both more open.
I found an interesting read putting the 118 and a un-baffled equivalent to the test burning in like structures.
In designing wood stoves it is important to remember that the completeness of combustion will be determined largely by the arrangement of the draft system. Efficiency demands two drafts - one to feed primary air to the coals for maintaining the basic fire, and another to admit secondary air to the region above the coals for the combustion of unburned volatile substances in the smoke. Ideally, both primary and secondary air should be preheated before entering the firebox, and both draft systems should be either independently adjustable or else preproportioned, so that the proper ratio of primary to secondary air can be maintained.
We should also remember that heat-transfer efficiency is increased by forcing the smoke to pass closer to the stove's surface on the way to the flue or by forcing it to take a longer path. Baffles, cooling fins, heat-exchange chambers, convection tubes and forced-air plenums are all worth considering when the stove is being designed. Often a fairly simple structural modification can result in a significant increase in heat-transfer efficiency.
The Jøtul company has published some interesting data on the comparative performance of wood stoves with and without these efficiency-promoting features. In an experiment conducted independently in Canada, two cast-iron stoves were installed in identical camp buildings 1-1/2 miles apart. One of the test units was a conventional box stove with neither baffle nor provision for secondary air (Figure 14.2). Airflow from the draft to the flue is
Figure 14.2 - Cross-section of a typical unbaffled cast-iron box stove. Airflow from the draft to the flue is direct, and there is no provision for secondary combustion of the smoke.
direct, and smoke may rush up the stovepipe unburned. The other was the Jøtul No. 118. The Jøtul incorporates a horizontal baffle that forces the smoke to travel toward the front of the stove and then through a top-mounted heat-exchange box before reaching the stovepipe (Figure 14.3). It also features a hollow door with asingle draft control on the outside and two ports on the inner surface. The air is preheated in the door cavity and then passes into the firebox through a primary draft near the coals and a proportionately-sized secondary draft higher up. This design is intended to promote complete combustion of the smoke just as it enters the heat-exchange box.
Figure 14.3 - Cross-section of the Jøtul No. 118 wood stove, distributed in the U.S. by Kristia Associates. Incoming air is preheated within the hollow door and divided into primary and secondary streams. Wood burns from front to back. Secondary combustion takes place as smoke is entering upper chamber.
Throughout the experiment, office clerks in both camp buildings kept careful records of indoor and outdoor temperatures and of the amounts and types of wood used. Although both buildings were maintained at essentially the same temperature and burned about the same proportions of hardwood and softwood, the standard box stove consumed 8.53 cubic feet of wood per day, compared to 4.25 cubic feet per day for the Jøtul No. 118. In other words, the conventional stove required about two cords of wood to produce the useful heat that the baffled stove squeezed out of one cord. And there was another notable difference:
The conventional stove was usually dead by 2:00 a.m., so that indoor temperatures often fell into the 20's by morning, while the Jøtul always held enough coals to start dry wood in the morning, and the indoor temperatures on corresponding days never dropped below 40. Anybody with a little training can pick out some unfortunate flaws in the design of this experiment, but on the basis of experience with both baffled and unbaffled stoves, I find these results entirely believable.
The above experiment was comparative only - it measured the relative efficiencies of the two stoves. The Jøtul company's engineering department has conducted other tests that shed some light on the interesting problem of absolute efficiency. Figure 14.4 shows the results of tests conducted on the same model stove used in the Canadian experiment. Notice that the overall efficiency starts relatively low, rises to a peak of 76 percent, and then declines as the firing rate is progressively increased.
I would guess that the efficiency is low at low firing rates because the stove is relatively cool, so that the smoke is below its kindjing temperature by the time it reaches the zone of secondary combustion, and leaves the stove unburned. At somewhat higher firing rates, everything works as it should, and the gases are more completely burned. When the stove is opened up still further, airflow through the unit is probably so rapid that the hot gases escape to the flue before they have had time to yield their heat to the metal, so that efficiency once more falls off. At the maximum firing rate, the overall efficiency is a shade under 55 percent.
This experiment demonstrates that the efficiency of a wood stove cannot be expressed as a single number, because it dependsso much on how the unit is used. In the previous experiment we learned that efficiency also depends heavily on how the stove is built. In the next chapter we'll plunge into stove design. If you are especially interested in efficiency, you might pay particular attention to the sections on drafts, baffles, and heat-transfer systems.
Figure 14.4 - Graph illustrating manufacturer's test results on Jøtul No. 118 shows the absolute efficiency. Overall efficiency starts low, rises to a peak of 76 percent and then declines as the firing rate increases.
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