Rocket heater with added thermal mass for small mountain hut
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- เผยแพร่เมื่อ 4 ม.ค. 2024
- I built the cedar hut in 2011. It is approximately 5.4m long and 3.6m wide facing south and well insulated. It has a gable roof so the loft space is usable as a micro mezzanine. The heater idea came from a Japanese TH-camr about 10 years ago. All I have done is taken it inside (after extensive test burns outside) and added the thermal mass.
It is important to note we live in a humid subtropical Köppen climate classification: type Cfa
This rocket heater thermal storage idea allows for efficient heating within a single hour of rockety burning, focusing on heating fire bricks. Once these bricks become too hot to touch, they store ample thermal energy, ensuring a cozy environment for several hours without the need for constant attention. This not only enhances safety but also grants the freedom to engage in other activities, knowing the room remains comfortably warm. After the burning phase, covering the heater’s horizontal and vertical openings prevents ash dispersion, leaving behind a safe, fire-free zone while the hot bricks continue radiating heat effortlessly.
A typical burn will go through 2.5kg to 3kg of bamboo or hardwood in approximately 1 hour. Bamboo typically creates much more ash.
The thermal mass will give off a good amount of heat for 3 to 5 hours +
The internal temperature taken at about 1500mm AFL typically gets to around 20° plus while it’s 3° outside. The mezzanine/loft would be uncomfortably hot and therefore I would fit a downdraught ceiling fan if I had electricity connected.
I’m still experimenting and tweaking, but aren’t we all😊 - แนวปฏิบัติและการใช้ชีวิต
I'm a sucker for rocket mass heater vids. Just posted - recommended in my YT feed. Aussie accent talking about first burn for winter - intrigued, I check out your channel and then it becomes clear - a fellow Aussie (wiser than me) living my future in the Japanese countryside, about 12 months ahead of me. 2024 is the year I end my (and my wife's) 21 year hiatus!
Same
It ain't the prettiest which not need for cabin.
very nice build, thanks for sharing.
Per your comment back... an insulated run of chimney or insulated flu to exhaust fireplace gasses solves almost all problems. Double walled stove pipe is expensive and this method is a much better insulation than that. Put 8 to 10 feet of stove pipe together (6 inch stove pipe). Then place a 8 inch or 10 inch (cheap) pipe, or dryer vent overtop of the smaller stove pipe. A small pipe inside a large pipe. Then "stuff" the space in between with vermiculite, perlite, or mineral wood insulation (if it won't get wet you can use the mineral wool.) The other two options for "outside." Basically, you buy the large dryer vent with two end caps. You cut out the six inch hole on the end caps that will surround the stove pipe. Then you can place the caps "back" at the end after you have stuffed the 2 inch space with insulation. Caulk everything with high heat stuff. With a long run of heated, insulated chimney, there are never any flu problems..... actually your draft could be so strong then in a rocket stove setup, it could get too hot !!!! As you know, many rocket stove setups need almost no "real chimney" or long run of chimney to still work great.... but you mentioned a flu issue so you may want to make your own insulated stove pipe !
I’m my experience thermal mass is not necessary but if you want to do it, it’s best used on the exhaust portion not the very hot portion. The actual stove itself should be free of any mass so that it will radiate the most heat into the room and it will extend the life of the metal. I have a steel tank rocket stove made with 2 inch sprinkler pipe and it has run now for years without any changes to the metal whatsoever and it gets red hot If you want the heat to last longer you’re better off putting your energy into making your house airtight and insulated. Also using thin metals will not last very long at all.
The "J" design (with open top) can have issues. You don't want to get smoked out if the conditions warrant it. As your "wood holder" tube heats up with an open top, the fire could "mistake it for its own chimney." You may consider increasing the stove pipe coming up toward you 10 inches, capping it after loading wood, and allowing 100% of the air to come from what you now have "capped," .... the horizontal tube. I would extend even that pipe a few more inches away from the wood burning as well but you probably don't have to. Trust me... if the top is left open there could be conditions "where it will want to burn up toward you a bit. If it's getting it's air from the horizontal run and you cap the top (above the tallest piece of wood,) there is no chance of "smoke out." You still should likely cap the horizontal cap with a few holes. When it gets going, it won't need to be completely open. What's best is to have a cap with a hole that allows a tube for outside air. Then, essentially, everything can be closed off.
Thank you for your comment and suggestions, I understand exactly what you are saying. I’ve been tweaking this heater for 5+ years including your suggested ideas, for example I brought Primary air from outside through a flexible expandable tube to the front of the burn chamber, and I didn’t find any noticeable difference in the burn, tried everything I can think of, and I found this works best for me.
Having said that, I will add an extension to the vertical feed tube once again as it may work now given the other adjustments I have added in past years.
The only negative aspect of this design in its present format is Backburn on windy days, and I need to find a solution to that. I thought of getting one of those fancy expensive whirly things to put on top of the flue and that may be the way to go.