Rocket Mass Heater for a tiny house?

Hi Permies,

Does anyone know of, or has anyone considered using a RMH for a tiny house? I have thought about the advantages and disadvantages including the space that is needed. Also, using cob might make it too heavy, but Paul mentioned that pea gravel is probably 1/3 of the weight, so that might be an option.

Or, for double duty, maybe a rocket stove that can be diverted into a mass and then to the exhaust?

Stewart

P.S. Shameless plug for our local group http://www.meetup.com/Tiny-Home-Co-Housing-British-Columbia. We will be meeting to discuss where to build our Tiny House Community.

For that matter, how small can they be built? Not just for small houses, but say one wishes to build a model of a rocket mass heater; how far can it even be scaled down? I imagine there is a minimum size to things, like air flow through a hole smaller than 1 cm is poor.

As a kid, we had a 8' a camping trailer we heated this way with a terra-cotta pot on the gas stove.
I would think in a tiny house, a rocket mass may be a bit much...
Have you thought about a portable rocket stove, perhaps even of stacked bricks? In the summer it could easily be moved to your outside kitchen.
Get a 5" or so long bolt. thread a nut then large lock washer, to about 2" from bottom of bolt. With pot upside down, place in bottom hole of pot. thread a large locking washer and nut onto bolt from inside pot. Instant handle to move pot. Hot pad is required for moving! I remember camping with snow on the ground, and being toasty warm inside. Perhaps, use several pots, rotating time on the stove then placed on metal trivets for additional mass?

Socrates, I think the smallest the RMHs can be is 6" diameter. Ianto and Leslie mention that anything smaller are less reliable (i.e., less consistent draft).

Joylynn ... I was thinking that a rocket stove might be a better option. A wood stove in a cabin is enough to heat up the place, but wanted to upgrade that cooking/heating system to be more than just radiant heat. That is a good idea. I should start looking at using a rocket stove that can be easily assembled and re-assembled for outdoor/indoor use. I am hoping that the indoor use would include a piping add-on that would transfer some of the heat into a mass for passive heating.

I like the earthen pot idea. The earthen pots can be placed in different parts of the tiny house for passive heat. Can they covered in a towel to prevent accidental contact with its surface?

Something like this is what I was thinking of.
https://www.youtube.com/watch?v=r66jjYdBmg8
Mind, I am not an expert at anything other than dreaming. My honey had a house burn down in his child hood, so for such to be approved here, at a minimum a welded frame would be added for stability. L shaped lengths, welded to make a box and rising corners to make it stable.

I have a rocket stove that is just a regular 20 litre metal bucket filled with clay/dirt with a can core, like this:



you can cook outside and then move the bucket inside to radiate some nice heat...

it's portable and movable so you can be pretty flexible with your approach but i guess you could go with something like this:



witch is not the perfect setup but can get you some nice results without compromising the weight of the unit.

Are you talking about a moveable tiny home or a fixed one? If it's a cabin, then most of the weight/distribution problems aren't there in the way they are for a tiny home on a trailer.

How big is the space? I have a full sized woodstove in my housetruck, so to my mind size to heat ratio isn't an issue either, that's more about how you manage the fire.

I think then it becomes an issue of design and being willing to have something less than the ideal efficiency to make it work in the space you have available. There's a recentish thread about someone wanting to build a RMH in a small space and looking at putting the mass under the bed.

Joylynn -- I watched that the other day, too, and it seemed like a perfectly good stove to make. Just starting to look for the fire brick, but hey, I could start with regular bricks just to make one even though regular bricks won't last. It won't work for an indoor heating/cooking unit for tiny houses, though.

João -- that is a pretty good idea. Once it has heated up, it will continue to give off heat throughout the night. Do you have any data on how much heat it can give off in a small room?

I like the sketch up model. Is that the one that you built? Are there two wood/fuel feeds, or is the L- section just for air intake?

Rose -- I am thinking of the THOW (tiny house on wheels) models. You're right about the cabin ones. They don't have the same problems as a movable model. In addition to using a heating unit like the wood stove you have in your housetruck, I was thinking of using a mass to store the heat. However, for a THOW, it seems that the earthenware solution might actually be a good solution for small spaces. Yes, I will have to search for that thread on an RMH in a small space. Thanks!

João Carneiro wrote:

could you explain that setup in more detail, please?

João -- that is a pretty good idea. Once it has heated up, it will continue to give off heat throughout the night. Do you have any data on how much heat it can give off in a small room?

I actually don't have any hard data, just the empirical experience of watching it radiate for hours, witch will be more effective when heating a small space.

I like the sketch up model. Is that the one that you built? Are there two wood/fuel feeds, or is the L- section just for air intake?

I did a google search to try and find something that would fit the purpose before drawing it up myself, found that nice image that in fact also comes from permies.com. I think that the L section is there to provide air intake, to try to prevent gases to climb up the wood feeder or even burn up.

"I like the earthen pot idea. The earthen pots can be placed in different parts of the tiny house for passive heat. Can they covered in a towel to prevent accidental contact with its surface"

I think a towel would work too much like a tea cozy, retaining heat rather than radiating it. But how about a chicken wire frame? Think: upside down egg basket.

Hi Stewart,

I'm not going to be constructing a mobile humble abode anytime soon, but I've been looking at radiant flooring for another project. But your post got me thinking. What if you combined a rocket mass heater, but the mass being a closed (looped) system water tank for the mass instead of coble/stones?

Closed system as it would need to be separated from potable water, (as it would need to be antifreezed for when the rocket stove isn't on if you live in a cold climate). One loop could supply the warm radiant flooring, another loop could go into a hot water tank, for showers and hot water for dishes. Depending how large and insulated your water tank, should be able to retain heat between firings.

I'd try to incorporate stove top cooking inside from the rocket stove heat, with an option for the flame shooting to a cooking grill station outside for bbq style cooking.

You'd probably want a door on the outside to throw the stick bundles into a closet that cold be accessed from the inside. Maybe cedar lined for insects from the sticks?

Ps, keep the air intake for the rocket stove air outside so you're not drawing in cold air from draft areas. I did a rocket stove pizza oven, that wasn't successful as the heat wasn't hot enough for cooking a pizza a short time that I was looking for. So maybe a small wood burning stove would work better.

@Socrates: here you have the original thread at permies where the project is discussed: portable 4" rocket mass heater - The Mass Bucket

Wonderful wonderful wonderful
These links have led me to 2 options i am very excited about

&

Particularly the rock-bucket idea is exciting. When finished, like 400 kg did he say [youtube]? But it's basically just about filling up your container with rocks. I see that as something that might readily be down-scalable, as well.
The other one [first pic] is also wonderful because it's a pretty simple instructable.

Well, Permies, this is what i was looking for. I'm very happy with this extension to my ideas and understanding of heaters.

Joylynn -- I didn't think about that. Yeah, that would sound like towels would have an insulative effect. How about creating a nook where the earthenware could be placed?

Paul -- I am not ready to start messing around with water (re: boom-squish) but open to the idea for the future. The specific heat capacity for water is one of the highest, but that also means that a phase transition from liquid to gas is going to be quite ... explosive. However, an appropriately placed blow out valve might be okay. I am mulling about heating a greenhouse (in cold climates for year round production, or maintaining tropicals) with heated barrels of water as the mass is probably a better idea than cob. Ultimately, a compost heated greenhouse (re: Will Allen) is one the best ideas to date.

As for function of a stove in a THOW, a rocket stove with a mass for heat retention, including the radiant floor heating, would be a good place to start, right? Also, for safety reasons, maybe if the stove is portable, set outside the TH, with a mount/unmountable connection to a piping system to a mass inside the TH, then, it can be fired up and then removed once the fire is out and the stove cooled down sufficiently. Thoughts?

Do you have pictures of your pizza oven? That is something that I would like make one day, too. It's amazing how an outdoor pizza oven can bring neighbors together!

Are you planning to make changes to your pizza oven design?

" I watched that the other day, too, and it seemed like a perfectly good stove to make. Just starting to look for the fire brick, but hey, I could start with regular bricks just to make one even though regular bricks won't last. It won't work for an indoor heating/cooking unit for tiny houses, though."
Is that because of a lack of a exhaust pipe? I'd imagined altering to change that somehow. Or is there danger of leakage through the loose bricks?

Stewart, The pizza oven went through quite a few changes as I progressed. Still working on the latest to bring down production costs and better heat control.
I'll try to post the picks:
The first I tried to make out of refractory bricks, but the unit wasn't rigid enough after construction.
The second pic shows the rocket stove prototypes I was experimenting with to see which would work best, no of them got hot enough for fast pizza baking.
3.0 Moved the fire into the cylinder and hot a top cook area (heat going around pizza) or as a iron skillet cooking area.

Oh sorry results pictures.

Paul, thanks for posting pics of your pizza ovens. The design has changed a lot from the first model. Can you regulate the temperature of the pizza oven?

Yes, can regulate it. There is a spatula looking round thing in the third picture. It can slip in and out of the direct flame area under the pizza. When it slips in, the flame diverts to the back chimney. (I could've bought a lever one to open and close, but this was just a prototype. When it is placed on the back chimney (like in the picture) the flames all go under the pizza.

Paul, I noticed that there is a horizontal cut in the heat riser. Is that a secondary air intake?

In the third photo you can see a spatula looking device with a wood handle on top of the back chimney. To regulate the temperature to the pizza cooking area, you put the "spatula" into the slot you mentioned, as a damper. When it is damping, the heat goes out the back chimney. When you put it on top of the back chimney all the heat goes to the pizza cooking area.

(The spatula was the cheaper option, a double wall heat riser and a double wall back chimney with rotating handle dampers, would be nicer, but this was still a prototype).

The nice thing about this oven, it only takes a half hour to be ready to cook pizza (pizzas cook in 3 or 4 minutes!) , I've heard the big built in ovens take two hours to be ready.
It is also portable, good for a tiny house! Inside the oven portion, I've cooked a picanha (like a trip-tip) and would like to try some bread one day. Underneath the pizza stone, is an iron griddle (that the flame makes contact with first). Remove the pizza stone, and you can cook burgers or what you would like on the griddle. Remove the iron griddle and you can have a direct flame to sear tuna, or boil water, make coffee. (also great for marshmallows). You can also put a wok there as well.

If you try something like this, make it more of a dome on top (my next project) so the smoke rolls over the pizza higher and doesn't roll across the pizza so close and get it too smokey. If you like it even less smokey, try charcoal. I've covered the pizza with a aluminum pan as well, for smokeless as well.

Enjoy.

Could this fit the need