Ok, I'll just start Are rocket stoves (RS) all "batch burn"? Matt's cooking stove, same question RS mass heater, same question also. RS are basically "gassers" in reality? I have a "gasser" boiler and realize it's efficiencies, using masonry as your storage may be just what I need in an upcoming attached barn (great room) for heating. Might eventually have to change my avatar
There are J’s, and they’re super efficient, but my opinion is the batch style is best. BrianK will be along soon.
No, the original rocket stoves were a simple L or J tube, like a Dakota fire hole, and required almost constant feeding but burned very efficiently. They were simply used for cooking. The subsequent rocket mass heaters using a J tube added a barrel above the J and a mass for the exhaust stream to travel through, scavenging the remainder of the latent heat from the exhaust stream to keep it indoors, but leaving enough heat in the exhaust stream for it to still rise out a chimney. These too required almost constant heating. The batch box was developed a couple years ago to extend burn times and get away from the constant feeding. Frankly even a batch box only burns an hour or two, but coupled to a mass, it burns hot and strong enough to “charge” that mass so the mass is still heating the room many hours after the fire is out. Matt’s cooking stoves are an excellent development of batch box principles. Coming from our perspective at FHC, only a batch box is based in reality - load it and forget it. No one has time to constantly feed a J tube. Yes, the rockets are all glorified gasifiers.
This is where I see the greatest potential for the rocket heaters. Instead of using Mass if they used water it would be a great replacement for an OWB. The biggest downside to the owb is the pure amount of fuel that they consume. If you put a rocket heater and it and somehow contain the heat and with the refractory. Would have the best of both worlds, I am sure there is a reason why this is not cost effective, I have no training in thermodynamics. However to get a mass heater into an existing home would require huge financial commitment also.
I have 8 years of living with a "mass" ie, concrete slab releasing it's heat via my radiant system, some relate it (mass) to a "flywheel" for heat storage. I'm wondering that the mass in the rocket stove & "bench" or bell is not really that much mass as compared to many yards of concrete in a slab. I'm aware that there are many variables but... * will one fire or "burn" heat this mass from room temp? * what is a reasonable temp of your mass to obtain for your off fire periods? * could this mean several burns or adding fuel to extend your burn? It's 4/15 and freezing rain/sleet and I shut down the boiler 3 weeks ago! This discussion is very comforting, even in APRIL!
I would think one would consider an indoor boiler before a mass heater. The indoor boiler, contained in the building envelope with hot water storage can provide heat on demand along with the benefit of batch burning as well as reduced fuel use as the “waste heat” from the system ends up being radiated within the heated structure. fuelrod to address your questions above, I would think the answers would depend on the size and surface area of the mass, the heat loss of the structure, any solar gain, outside conditions of temperature and wind, desired indoor temperature, etc, etc... As with a FHW radiant system, the desired indoor temperature can be obtained with a lower water temperature if the heat demand is low. Higher heat demand requires higher temperature for a given sized heat exchanger... A calculation of BTU demand would determine whether one fire, or multiple successive firings would be necessary to achieve the desired temperature (potential energy) of the mass. Similarly, refiring to maintain that temperature would be determined by the heat loss.. I can only imagine the challenge associated with rapidly changing ambient conditions as we have sometimes in NE.. imagine heating the mass to deal with a windy cloudy 25 degree day and then a warm front pushes 70 degree temps the next day.. open doors and windows might be necessary to avoid overheating.... I think if I was to do a rocket mass heater in a house, I would use it occasionally as a heating supplement and not as the primary source of heat... JMHO. Interesting discussion.
stuck, I have an indoor wood "gasser" boiler, love it. We're thinking of building a semi detached barn or great room to our small house. It would not be practical to run lines to it from the wood boiler and it's use would be "spotty" during the heating temps. I'd rather just have the ability to "bump" it up for times of use, tending a stove is what we had envisioned but cooking abilities would be real nice along with the visual & cool factor of a r/s compared to a w/s. I'd really like a "Russian furnace" or stove, but that looks like it's a much more & complicated build, but the simplicity and efficiencies of a r/s are a big plus.
Curious as to why it would be spotty. Do you have storage? Does your indoor gasser barely keep up in the coldest temps? I think a rocket mass heater would be awesome, but I guess it’s practicality is situationally dependent..
No, my use of this new space will be spotty (in the ''deep'' heating season). Keeping a slab warm for possibly weeks in an empty "great room" is something I don't want to do. Then there's the 60' or so that I'd need to run supply lines, that would have to run outside underground.
That makes sense then. So you would fire up the rocket mass heater several hours prior to use of the space and then just let it cruise until you are complete with use allowing it to cool to potentially below zero depending on outside conditions... Another option would be to use glycol as your heat exchanging fluid. You could run a zone off of your boiler to a superstor (or similar) and fill that with the a propylene glycol mix that is good down to -60ish degrees. Similar to ice melting systems for driveways, you could allow the system to go well below zero before there is any concern. If there was a concern about freezing, we would likely be entering the next ice age... with a setup like that, you would likely need some sort of tempering valve to prevent thermal shock to the zone pump upon startup as well as a mixing valve to prevent the slab from getting too hot. I’d imagine the mixing valve would be best installed as close to the heated space as possible kind of like when one uses a FHW system for radiant floor heating. These people have some good information. Takes a while to find the info though. https://www.uponorpro.com/~/media/e...1201jlc edits121714.ashx?version=100620150856
Exactly I'm undecided on the floor, as simple as a slab is to do, I'm wanting a semi finished barn look & feel (sawmill finish floor) to it, yet I hate the added cost of a crawl space for an insulated floor.......... so that's another reason why I'm swaying away from radiant, I think the mass of a slab is huge for in floor radiant. I wonder about the "lifespan" of a framed floor that's just high enough off the grade to work under (applying pt plywood) then filling the joist bays with either rigid or spray foam (maybe a combination)? The older & more stiff I get the faster I get claustrophobic, getting under there for repairs or maintenance is a sucky job even for a 20 yo. Boy I'm all over the place with this one day 3 of really junk weather will have that effect
If you’re going to go with a crawl space, I would make sure that space is conditioned too. Insulate the exterior foundation to retain the heat. If you don’t make the crawl space part of the conditioned space, you will need to ensure that you properly manage moisture via either air exchange or dehumidifier. It’s too tempting to close off vent openings thus restricting the moisture’s escape path and ending up with rot or mold. I was in an old barn a few years ago that had exactly that happen. Floors sagged over a foot due to rot.. I think the amount of heat you’d lose through the floor would be minimal if the foundation is insulated. You could also dig down a bit and lay rigid foam as they do under poured slabs and then just back fill on top to add thermal mass to the building envelope. This would help with the small heat loss through the floor. Another thing to think about is how fast you want to take the space from say 10 degrees up to 70 or so. The mass of the objects/material and air inside the building envelope will determine the speed. For a given number of BTUs, more mass will take longer to heat. If you’re only going to use the space for a day at a time, a mass heater may require more fuel than is acceptable to get the temps you want only to slowly dissipate the heat over a long period when the room is not in use. Mass heaters provide a steady consistent heat... they don’t allow you to heat or cool a structure quickly.
^^ Yes, I'm with ya on the moldy poorly vented crawlspace..... for all that cost (frost walls & "rat" slab/insulation), what's your thoughts on a "closed" insulated conventional framed floor on posts?
You talking about framing and then spray foaming from the bottom? I guess I don’t have enough knowledge to comment on it... a closed cell foam would prevent moisture from coming up from down below. But would prevent the wood from breathing to let moisture out if the space cooled and condensation developed in the floor. This is beyond my knowledge to make an intelligent comment on..
^^ Yes. I just built a similar condition where I have a 4' cantelever on the 2nd floor and filled the "joist bay" with rigid p-iso foam (10"). Below this space is outside air and above is a br. floor. It naturally colder the the floor above a conditioned room, but far, far from the outside temps. From what I have been told & understand about condensation in walls. you want your dew point IN the foam, and a minimum of 2" is needed for that. I don't see why this would not be the same for a floor.
What about a board floor laid directly on the concrete slab. It would heat the room up just slightly slower. But wouldn't cool down quite as fast.
I'm worried that a (cold) slab, even insulated would work against me when trying to do a quick heating of the space for a get together. I've seen a lot of AK homes (on tv) built on poles, is that because of the cold, soils or permafrost? How are they typically insulated?
I guess I disappeared on this one . Very sorry about that !! Several reasons to build on posts. In the Arctic, it's to allow the ground to stay frozen year round. . Tho that often doesn't happen without Thermo Syphons or refrigerants. On muskegs , people build on posts, well, because they are building on a muskeg. Not much solid under a muskeg and being on posts/pilings makes re leveling easier several times a year. On the coast, they build on pilings because it's faster to get something level , solid enough to build on and costs.
