Marine Russian Stove: Heat Storage

This is the next in a series of posts devoted to solving the problem of fitting a traditional Russian stove aboard a boat. It is interesting to see how the concept evolved based on feedback from the readers, following the same pattern that the entire Quidnon project has taken, where half-baked ideas eventually turn into fully baked ones based on good ideas contributed by knowledgeable, experienced people.

The reason for the name is that this stove will do everything that a traditional Russian stove does: it will provide space heating, a warm place to sleep, hot water for washing, heat for cooking, and can be used to heat rocks for a sauna/steam room. But the Russian stove is a massive piece of masonry erected on its own foundation, and masonry doesn’t belong aboard a boat except perhaps as ballast. (The distinctive red bricks out of which much of Boston was built had sailed over as ballast aboard British ships and were so plentiful that the colonists took to paving sidewalks with them.)

And the reason for including not one but two marine Russian stoves in Quidnon’s design is to make it possible to travel and live aboard a Quidnon in Russia, and overwinter aboard in places where rivers freeze solid and temperatures can stay below -20ºC for weeks on end, but where there is generally plenty of firewood available. Quidnon’s hull, made up of 3cm or so of plywood and insulated with closed cell foam and radiant barrier, and hauled out on a riverbank, replaces the traditional log cabin. To keep it warm, the marine Russian stove replaces both the traditional Russian stove and the stove used to fire the Russian banya (sauna, if you prefer Finnish).

On board, all of these many functions provided by the use of masonry in a traditional Russian stove have to be arranged for in other ways. Space heating is provided not by radiant heat but by forced warm air; hot water is produced using a heat exchanger; cooking (and heating up sauna rocks) is on a stovetop rather than a pizza oven-like vault. (Heat can be directed to the stovetop—or not—using a baffle.) With the stovetop shut off the stove will generate minimal radiant heat, allowing its heat output to be piped and ducted to where it’s needed. (Who needs extra-hot galley or heads?) Heat is stored in the hot water tank instead of within a masonry structure. In a wood-fired stove, masonry can get four times hotter than water can get under atmospheric pressure before turning to steam, but water has about four times the heat capacitance of masonry.

Most of these concepts have been worked out already and described in the previous posts. The only new element I have added since then is a water-to-air heat exchanger around the hot water tank: forced air will be made to flow around all six sides of the water tank. Thus, it will be possible to fire the stove in the evening long enough to get the water hot, then use that heat to produce warm air all night. On colder nights this may not be enough to keep the entire cabin comfortable, but with the hot air ducted to where people are sleeping it will at least keep the berths warm: a boat-sized hot water bottle. The position of the hot water tank is directly below the stove itself, keeping the runs of plumbing very short and placing the mass of the water low down where it will add to the boat’s stability. The hot water tank is integrated into the structure of the stove, and this will save on materials.

This stove will ship as a kit consisting of sheet metal shapes plasma-cut and bent on a brake so that they can be assembled using hand tools. The kit will be designed to pack flat efficiently, and will include all of the plumbing, hardware, insulation, sensors and electronics (a programmable controller for regulating the flow of fresh air from outside, for dialing in air and water temperatures, plus an alarm for when it’s time to add firewood) and a thermoelectric generator to power the control circuitry (and for charging phones and laptops).

This stove is a marine stove, meaning that no effort will be made to certify it for residential use. Some locales regulate wood stoves more strictly than others, and it’s up to you to figure out if you can (or have to) use it legally. Keep in mind, this is a stove that two people can lift and move (with the water tank drained) and so it doesn’t have to be a permanent installation. If you have a fireplace that’s grandfathered in, then you are probably good to go. If not, you’ll need to install a flue somehow. It may be a bad idea to use this stove in an urban or suburban environment in what currently passes for “developed” countries (i.e., litigious and riddled with bureaucracy). But there should be few issues with using it in a rural environment, especially on a homestead.

If you use it on a boat, then the standard marine disclaimer applies, which goes something like this: “Please check your local and federal regulations concerning the use of wood stoves aboard.” But it should, by its design, pose many fewer risks than most marine wood stoves. It will be insulated with rock wool all around and remain only warm to the touch even when fully stoked, making it safe to use around toddlers. It cannot be made to overheat the water, and will automatically shut down the hot water circuit by emitting a puff of steam. And it will regulate the burn rate as needed by adjusting the amount of fresh air pumped into the combustion chamber from outside. The firebox will remain completely sealed off from inside air (except while adding wood) minimizing the chance of CO inhalation. The kit will carry product liability insurance, but anyone filing a claim would have to answer a simple question: Did a qualified marine surveyor approve the installation?

I hope that this stove design will turn out to be very useful both on and off boats. It can be used to heat a cabin in the woods while providing cooking and shower water. It can be used for summer cooking, canning, and to keep greenhouses warm during cold spells by piping in warm air. And arriving, as it will, in the form of a lightweight, flat-pack kit, it will be possible to install it in roadless locations such as cabins up in the mountains, where hiking in a masonry or a cast iron stove would be too difficult.

So, how many of you would consider buying this stove? And how much would you be willing to pay for the kit to build one? It would be very helpful to have some indication of the level of interest before committing resources to working out the detailed design and organizing the fabrication process. Potentially, the sale of kits for building this stove will offer us a way to financially bootstrap the project. It will also allow us to get our feet wet with managing the logistics of producing kits, so that we can learn by making mistakes that are small and cheap rather than boat-sized and very expensive.

For those who have been Quidnon fans for some time, I hope that you will find the bootstrapping approach appealing. I see it as a potential way to keep the emphasis on building some excellent boats rather than on hurrying up to making money to pay back investors.