smallest rocket mass heater

For small rockets. I think the best option is 4 or 5 inch batch rocket. They work nicely.

Here's an example of one of my builds. 12cm heat riser, just a smidge below the 5 inch mark.

https://permies.com/t/35569/rocket-stoves/Range-retrofit


This type of core can be used in plenty of other situations.

Glenn Herbert wrote:Jaime hasn't posted since 2012, so he probably isn't going to see your question.
I would probably drill a pilot hole, then use a scrollsaw/saber saw/whatever name you know it by, then file the edges to clean up.


And to answer the question you didn't ask, I wouldn't try to copy that build for a permanent installation. A 3" stove isn't going to put out a measurable amount of heat without feeding round the clock, and the metal innards will tend to conduct heat away from the combustion zone and cool the already tiny fire. If you want a small RMH, you need a highly insulated combustion zone of refractory (ceramic) materials to allow enough heat buildup for complete combustion and withstand the corrosive atmosphere inside a high-temp fire. Without complete combustion you will get creosote in your chimney and in any heat transfer ducts.

How small is your small house? There have been a few 4" systems successfully built and published here.

Thanks Glenn. I found this family's design some time ago and asked if they could send me some design specifics, but for some reason the father didn't really want to.

http://www.mylittlehomestead.com/rocketstovespaceheater.html

I kept their website info. because what they built would be PERFECT for my house. I was just trying to find ideas/videos/ (and I don't mind paying for the info. either, if I could find it) that would go into more build detail so I could build one as close to their design as possible. Only thing I don't like are the legs they put on...other than that the size is perfect.

My house is 115yrs. old. Right around 600 (and some change) sq. ft. interior living space. My living room is only 14x14ft. That is the largest room in the house. There is a chimney in the living room with a 6 1/2 inch flue opening. Apparently at one time, someone had a wood stove hooked up. I haven't had anything hooked up to it. When I first moved in, the heating source was a propane furnace. I used that money draining monstrosity only one year and it destroyed me financially.

Anyway, I went to Kerosene. K-1...because my family was in the bulk fuel and fuel oil (diesel, kerosene, etc...) business. I bought a Dyna-Glo portable heater. Puts out (supposedly) 26,000btu. It's what I still use for now. I live on a 2acre parcel full of trees and trees that have fallen. So I have plenty of free fuel!

The other thing I like about their design is that it looks to be about the same size as the heater we used when I was in the Army. The H45 space heater. I was a Hawk Missile radar operator so we had a decent size platoon that needed a large tent. That tent was bigger than my house! Anyway, it was set up for two heaters. You usually only need one because by the time everyone was in and you had that thing fired up, it was all you needed. (especially using MOGAS!) Sometimes it was cold enough for two. But not usually. Anyway that thing puts out 45,000btu. I was thinking about getting one of those if I couldn't build or get someone to build for me, a space heater like the one this family built.

When I get to it, I plan on removing the old furnace from downstairs and building a more traditional RMH with thermal battery. Right now I have another Dyna-Glo downstairs that I only fire up when it starts dipping below 25 deg. Makes a HUGE difference though when I use the one downstairs because of the heat rise. The flue to the other chimney for the furnace, looks to be about the same as the one upstairs. But that's for another day...long away from now!

I really appreciate you taking the time to respond.

Thanks.

Fred

I'm new to this forum so I'm still learning how the posts work. I posted (or at least thought I did...ha!)to you Glenn Herbert. But I used the quote feature. Didn't realize where the Post Reply and Quick Reply buttons were. Anyway my response to your questions seem to be on the next page. Page 2. Thanks again.

Fred

Ok!...Now I see how this forum works! Forgive me guys! (and gals!)

For a place where useful information is shared, it is much better that all posts be sequential so new comments are always visible at the bottom, and nothing gets missed because it was a response to something on the last page. (I do like the feature of some forums where posts are numbered and it is easy to refer back to a specific post.)

On those plans..."We thought we followed the internet examples very carefully." That's the problem, they followed youtube videos Looking up information from experienced professionals would have told them two things from the start, that an all-metal rocket heater that burns efficiently will destroy itself soon, and that you need a good chimney for nearly all situations.

It is possible to build a small, relatively compact and low-mass RMH, but you need to use well-insulated refractory ceramic materials for the combustion core. What these folks have is mostly a rocket-shaped woodstove, which needs to burn constantly to give out any heat and cannot be burned slowly to avoid roasting the occupants in mild weather. A RMH can be burned for a short time if only a little heat is needed for a day, and it will not overheat the space or need constant tending all day.

A full-size RMH in your basement is not likely to work well. It is primarily a radiant and conductive heat source, and you will heat your basement more than the upstairs. Also, it needs to be where you can see and hear it all the time it is running so you know when it needs feeding. Out of sight, out of mind, and you will find it going out because you forgot to feed it, or wasting time and energy running up and down stairs to check on it.

You can make a good RMH right in your living room replacing an existing couch or chair, where it will keep you gently warm and you can tend it easily. A 6" system should do fine for a small house and can be pretty compact. You plan on putting the heater in your living room, correct? Just take the clearance you would need for that and put down some brick spacers and a masonry surface with air circulation beneath it, then make a small 6" firebrick J-tube with barrel connected to your stovepipe opening. Stack bricks or other mass around this as needed to absorb some heat. There are more details to cover, but that's the essence of what you could do quickly and easily.

Glenn...much appreciated. These few posts have been SUPER educational. I keep you up to date on what I end up doing. Thanks to everyone else who also "educated" me.

I am testing out a 4" J-Tube for a small rocket mass heater. It does seem to have limitations on burn velocity inside of a 55 gal steel drum. I do not know if a secondary air supply needs to be used to help burn hotter, or how that would be accomplished if it were needed. Thermal mass inside the drum is through cement pavers (free) and I'm thinking of using clay/gravel mix to fill gaps between pavers.

Hi John,    Over the years, many experiments have been done with adding secondary air to J tubes. In general, the verdict was that it did not improve combustion - some even hindered it by cooling the fire.
The best modifications that were tested and proven to improve combustion in a J tube was Peter van den Bergs P-channel and Tripwire

You might find some helpful information in this thread: Peter van den Berg 4 inch Minnie Mouse rocket mass heater.

Hi. In case my cabin's thermal mass heater can give anyone any ideas considering the present focus on small rocket mass heaters, I'll try and post a picture...



It's slightly smaller than a 4 inch J-tube system. I used Matt's ghetto casting for the core. It works like a bomb! Heats up a 12 square meter cabin in 5 minutes, and I have to run it on low. Might not be suitable for much bigger spaces in very cold climates though...

Dear Ernie, Erica, and other RMH enthusiasts,

After reading this thread, I understand that rocket cook stoves and space heaters under 6" can work well, but RMHs with long runs of exhaust under 6" often don't. What about an RMH like Kirk Mobert's Cyclone? It seems to have a relatively short exhaust system. Do you think something like this could be scaled down? If so, to what size?

The batch box combustion core (as in the cyclone in the link) has been demonstrated to scale down, to as little as 3" I think, with a bell style heat exchanger. The J-tube would not scale as well due to surface-to-volume effects.

The cyclone appeared to come out perfectly sized for efficient function, and if it had had a metal radiant panel built into the bell for instant heat it would probably still be in use. A smaller version might need the internal surface area tweaked a bit for best function, but would be an interesting experiment.

It seems people will ask about a 5" or smaller feed to make a "smaller" RMH, but that feels to me like the wrong way to look at it. First you will find it tough or impossible to clean out the burn tunnel of ash if you can't reach inside, and if you build a 6" system just place a brick over half the feed and now you have
the smaller system.

For a compact/lighter RMH I would suggest checking out Uncle Mud's Cottage Rocket, as it can be a self-contained unit in a 55 gallon barrel, and just a couple hundred pounds of mass at most inside. You sit it on top of a couple bricks to allow airflow underneath to protect the floor and you're good to go.