Why dont we all want rocket mass heaters?

[electrathon]

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https://www.hearth.com/talk/threads/mh-puzzling-together.155464/#post-2089184

I don't think open fireplaces are allowed in new construction in Oregon. But you say RMH's are? My sister lives in Portland and wants a masonry heater. I gave her all the hardware for one and plans. We'll see......

I saw on the site that they said that some areas are allowing them. Portland was used as an example place. It is possible it is not true. I am not sure about fireplaces, I will have to ask our inspector about that.

 

[tpenny67]

I've got to wonder how any heater that relies on thermal mass would work in New England where 40 degree temperature changes in one day are common. Unless the house is uber-insulated, it seems that by the time the time the thermal mass is warm enough for a sub-zero night it will be baking the house the next day when a warm front comes in.

Also, from the little I've read online, one potential problem with a rocket heater is back drafting on a windy day at the beginning and end of the fire.

 

[electrathon]

I've got to wonder how any heater that relies on thermal mass would work in New England where 40 degree temperature changes in one day are common. Unless the house is uber-insulated, it seems that by the time the time the thermal mass is warm enough for a sub-zero night it will be baking the house the next day when a warm front comes in.

Also, from the little I've read online, one potential problem with a rocket heater is back drafting on a windy day at the beginning and end of the fire.

I could see the thermal mass issue being a problem with overheat or too long to heat up. I would guess it is similar to having a floor heat system that has cement as a floor. As to back drafting, it seems that it would not be that different from a conventional stove. I was curious on how hard it was to get the draft started they seem to have a complicated chimney path.

 

[tpenny67]

I could see the thermal mass issue being a problem with overheat or too long to heat up. I would guess it is similar to having a floor heat system that has cement as a floor. As to back drafting, it seems that it would not be that different from a conventional stove. I was curious on how hard it was to get the draft started they seem to have a complicated chimney path.

My understanding (could be wrong) is that rocket stoves have a much cooler exhaust and sometimes don't even have a conventional chimney at the end. They rely on a raging fire in the vertical section to keep the air moving, and when that raging fire dies down...

Also, since standards are lacking and most rocket stoves are individually designed and built, there's plenty of room to make a bad design.

 

[electrathon]

My understanding (could be wrong) is that rocket stoves have a much cooler exhaust and sometimes don't even have a conventional chimney at the end. They rely on a raging fire in the vertical section to keep the air moving, and when that raging fire dies down...

Also, since standards are lacking and most rocket stoves are individually designed and built, there's plenty of room to make a bad design.

I have read that the exhaust is very cool, much like or even exceeding a modern wood stove. The wood, wood gas, creosote is almost all burned. As long as there is a vertical stack the draft should continue. This does rely on a lot of other factors though, mainly positive verses negative pleasure in the house. If there is not an outside air source I could see someone turning on a bathroom fan or similar and reversing the draft. We already have that issue with our stoves though, as you said, worse during start up or shut down cycles.

 

[Poindexter]

I looked into this a few years ago.

My blazing success was a 'pocket rocket'. 5 gallon metal bucket with 48" of four inch exhaust stack, maybe 18" of 6" swsp as the fuel magazine and a 9" cone of orange glow at the top of the stack. If id had a safe platform to stand on a couple feet above grade i could grill some killer crusts onto some ribeyes with that.

I built several J stoves, all outdoors in the snow.

Throat diameter is the key dimension. J stoves with a 4" throat will not run dependably on cord wood no matter how small it is split, at least with my local trees. Twist and bow in the splits causes the a:f ratio in the burn chamber to vary.

I did get a couple 6" throat J stoves running pretty good in cord wood, but even then something like 80% of my cordwood is too twisty to bother splitting smaller.

If the wife and i sell our big house on the small lot and move to a small house on a big lot i will probably put a sofa shaped rmh on an outdoor patio.

A lot of the threads on permies, when i was active there were "i bought the book, didnt follow the directions and now my stove doesnt work right."

If you are really curious, the pdf for a pocket rocket was free. Build one of those first. Crazy amount of heat out of a few little sticks, right now.

Second, google up ' dr peter rocket stove', should get some links to a phd in holland...

Third, buy the book from permies, 16 bucks i think for the pdf, but rtfm and follow the proportions.

 

[electrathon]

Poindexter, thank you for the input. I will read up more. " Crazy amount of heat out of a few little sticks, right now". This is what got me really curious. If altering the way we are burning gets more heat it seems it would be a very good thing. How much did you have to tend to the stove? Constantly, off and on or about what happens with a wood stove? It seems that if the main concern with them is having a fire going inside your house you could have the initial firebox opening outside, then have the thermal mass inside the house. Possibly having to go outside to tend to it would be uncomfortable.

 

[Poindexter]

Poindexter, thank you for the input. I will read up more. " Crazy amount of heat out of a few little sticks, right now". This is what got me really curious. If altering the way we are burning gets more heat it seems it would be a very good thing. How much did you have to tend to the stove? Constantly, off and on or about what happens with a wood stove? It seems that if the main concern with them is having a fire going inside your house you could have the initial firebox opening outside, then have the thermal mass inside the house. Possibly having to go outside to tend to it would be uncomfortable.

I don't know that it gets more heat, just the rapid primary and secondary burn can get all the BTUs out in a hurry. Just like a raging fire in a masonry heater.

The RMH basically uses adobe instead of stone as the mass storage device.

I have thought for years it would be handy for "someone" to get a firebox and secondary burn chamber of a typically sized masonry heater through the EPA testing process so home builders could just install a EPA approved masonry heater and then box out the smoke path however works on the floor plan. Heaven forbid the EPA spend my tax dollars on that.

Once the critical dimensions are known, the developer who sunk a million bucks into testing will never sell another one and will never break even on the "approved" design.

 

[bholler]

I have thought for years it would be handy for "someone" to get a firebox and secondary burn chamber of a typically sized masonry heater through the EPA testing process so home builders could just install a EPA approved masonry heater and then box out the smoke path however works on the floor plan. Heaven forbid the EPA spend my tax dollars on that.

Uhhh the epa would not be spending any money on it at all it would be the manufacturer who spent the money on development and testing. And the smoke path would have to be predetermined as well that has a lot to do with how the stove would operate.

 

[begreen]

The Alliance for Green Heat instrumented a kachelofen and a dragon rocket heater for 3 days of testing at the first stove decathalon in D.C. The masonry heater performed very well and Matt's modified rocket stove impressed the judges.
http://www.forgreenheat.org/stovedesign/finalists.html
http://forgreenheat.blogspot.com/2013/12/a-brief-analysis-of-stoves-at-wood.html
@John Ackerly can provide more details on the testing. John, do you know what Matt is up to lately?

 

[Poindexter]

Uhhh the epa would not be spending any money on it at all it would be the manufacturer who spent the money on development and testing. And the smoke path would have to be predetermined as well that has a lot to do with how the stove would operate.

While I agree the former is the standard operating procedure, I find it unfortunate. I have no idea what the EPAs budget was last year, but I bet it was enough for a couple guys to log off facebook long enough to build and test a couple prototypes through certification.

For the latter, any vehicle owner in the US, last I knew even in California, can install any exhaust they want from the outlet of the catalytic converter on back. Subject to state and local noise regulations of course, but as long as the emissions equipment is unaffected custom "cat backs" are federal legal. A well designed masonry heater should be the same. Once the primary and secondary burns are complete in the first two chambers, the exhaust gas should be legal and the rest of the piping between the secondary chamber outlet and chimney cap is of no concern to the emissions regulators.

What I would like my tax dollars to be spent on, and what my tax dollars are actually spent on are two entirely different realities.

 

[electrathon]

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What I would like my tax dollars to be spent on, and what my tax dollars are actually spent on are two entirely different realities.

You do have to be careful about this sort of thinking. As of today, you my be happy about the results. As of yesterday you may not have. They could have taken your dollars and used the money to attack wood burners like they used your dollars to try to put the coal industry under and force an entire part of the country onto public assistance. Sometimes it is better if the people do things without the "help" of government.

 

[jetsam]

Rocket stoves are a big deal for cold people who have access to stone or clay and wood. It's at least an order of magnitude more efficient than an open fire.

I won't be swapping out my BK for one, but it is good to know the principle. I'll be surprised if I don't find an ad hoc use for a cinder block rocket at some point.

 

[bholler]

A well designed masonry heater should be the same. Once the primary and secondary burns are complete in the first two chambers, the exhaust gas should be legal and the rest of the piping between the secondary chamber outlet and chimney cap is of no concern to the emissions regulators.

The difference is that the venting system of a wood burner determines the draft and on a masonry heater if the internal heat exchange passages are not designed correctly regardless of how good the combustion box design is it will not work. If you think that nothing past the combustion chamber has an effect on the emissions you have allot to learn about wood stoves.

like they used your dollars to try to put the coal industry under

The economics of coal mining and the availability of cheap natural gas is what put the coal industry under. It was on its way out long ago. Believe me I live in coal country the coal industry died on its own.

 

[bholler]

I bet it was enough for a couple guys to log off facebook long enough to build and test a couple prototypes through certification.

Do you really think that the epa has stove designers on staff?

 

[Poindexter]

Had a bit of a bad dream over night. The hotrodders putting cat back on modern vehicles, in general, are looking to maximize airflow for best acceleration.

@bholler is correct that hanging enough pipe or masonry, on an otherwise clean burning fire box, can turn it into a heavy smoker.

 

[Poindexter]

Rocket stoves are a big deal for cold people who have access to stone or clay and wood. It's at least an order of magnitude more efficient than an open fire. I won't be swapping out my BK for one, but it is good to know the principle.

Pretty simple, but I agree burn a small of wood or dry grass hot and fast in the rocket stove portion of the assembly and then store the heat in a mass of adobe or stone. I won't be swapping out my BK either.

It would be handy for me to have a masonry stove of some kind with one surface taking up a section of the garage wall. When my wife gets home from work with her cold car I could fire thing hot and fast and use at least some of that heat to warm the garage and her car back up without having to burn oil to do it.

I'll be surprised if I don't find an ad hoc use for a cinder block rocket at some point.

The cinder block rocket doesn't work for beans. What you see in the youtube is about all it can do, no secondary burn. I experimented quite a bit last summer.

My church is one of many that sends teams annually to knows how many orphanages there are in Haiti. Our particular group of kids is running out of wood to cook what food they have. While everybody else in the congregation was praying for a solution, I decided to build a cinderblock rocket to see if I could get it running on dry grass.

Got some dry hay from a neighbor with a couple horses, and split some of my straighter cord wood pretty small. I built the first one as shown on youtube, and WYSIWYG, no secondary. The throat on that thing is in the wrong place for starters, and the vertical isn't tall enough for another.

I dug my bentonite clay out of the tool shed (handy stuff, bentonite) and got to sculpting and sealing. At the extreme I filled the elbow with enough bentonite to put the throat where it belongs and fabbed up a P-channel out of sheet metal to introduce preheated turbulent air just down stream from the throat where secondary burn should be igniting. If you get one working good with a dependable secondary burn going on please do send me a PM or start a new thread.

The pocket rocket will work, very well, the first time. Here is the exhaust cone on mine.



I am not finding the exact .pdf I built from this morning, but any of these should work well.

https://canadiandirtbags.wordpress.com/2010/12/05/how-to-build-a-pocket-rocket/

http://homesteadlaboratory.blogspot.com/2014/01/pocket-rocket-stove.html

http://www.rocketstoves.com/pdf/pocketrocket.pdf

If the neighbors aren't pulling back the curtains to see the jet airplane crashing into your back yard, well, you don't have enough draft and it isn't really a rocket stove yet.

 

[HisTreeNut]

I made a tin can rocket stove after watching a plethora of on-line videos. The stove does generate a serious amount of heat. Looking at a few other videos in my research, a rocket stove is imho a mini-forge. You could melt metal with this thing if you wanted to.

You can also use the stove to boil water. Watching videos, the stoves will need a gas stove burner grate [or something to that effect to allow gases & heat to escape]. If you don't, your fire will not burn correctly and/or die out. That being said, a properly built & vented stove will boil a couple of cups of water in 2 - 4 minutes. A gallon of water boils in 8-12 minutes in the same situation. Covering the pot allows for faster boil times.
Once I got mine working, and the novelty wore off, I used it as a marshmallow roaster. About 10 minutes to get hot, and it roasts marshmallows in about 5-10 seconds.

I made a video of the rocket stove in my fireplace before we installed the Buck. At this moment, i cannot figure out how to upload or post it. Anyone know how to post an old iPod video?

Mistakes I have seen in people's videos:

1) In most of the videos of the tin can stoves do not have enough height in the chimneys. You should see virtually no smoke coming from the top of the stove and without out height, the gases do not re-burn well, much less re-burn at all. Most videos show a raging fire and smoke billowing everywhere. That is not what you want at all.

2) In a lot of the videos, you see flame coming out of the top of the cans. If you see flame coming from the top of the cans, there is too much wood in the stove or the wood has not burned down enough to cook and so on.

3) Even though I "insulated the can with ash," the can still gets ridiculously hot...I used duct tape for the test because I couldn't find my aluminum tape anywhere [in a a box. It started melting after about 30 minutes & I sprayed the tape with a water bottle to slow the inevitable melting process...the water that hit the metal evaporated almost instantly. If you were to build one of these things, I would not set up the stove on top of a table directly, but I would place it on some bricks or stone of some kind.

FWIW, it is a neat "technology" and something fun to play with.

 

[mjstef]

I ran one in my greenhouse in Montana. Gotta find the pics. Most all heat is absorbed in the mass and nothing but vapor out the flue. I could get to the entire loop in my greenhouse through 3 cleanouts. Being it's so efficient it burns very little wood and never got more than a cup or so of creosote ect out of 40' of pipe.

Anyways when i get my hunting cabin built i will likely do one their. Wife likes something like this..... https://i.pinimg.com/736x/7a/c2/07/...610b6b9b--rocket-mass-heater-thermal-mass.jpg

http://www.terre-et-flammes.fr/portfolio/seine_et_marne/

 

[putttn]

I ran one in my greenhouse in Montana. Gotta find the pics. Most all heat is absorbed in the mass and nothing but vapor out the flue. I could get to the entire loop in my greenhouse through 3 cleanouts. Being it's so efficient it burns very little wood and never got more than a cup or so of creosote ect out of 40' of pipe.

Anyways when i get my hunting cabin built i will likely do one their. Wife likes something like this..... https://i.pinimg.com/736x/7a/c2/07/...610b6b9b--rocket-mass-heater-thermal-mass.jpg

That is a Rocket Mass Heater. Probably very similar but he does not use any stone or mass to retain the heat.

 

[georgepds]

OK, the constant feed part makes since. I was wondering how fast the consumption was when they were rocking. I do see that they are allowed in Portland Oregon, a good example here of what is safe, allowable or legal in one place but not elsewhere. If you read through some design plans, the concept can be pretty small, likely only a few hundred pounds. That small though and it nullifies the idea of only a fire every day or two.

Is it because it's always raining in portland?

 

[begreen]

Moved the Liberator to its own thread so that this one can stay on the topic of rocket mass heaters.

https://www.hearth.com/talk/threads/liberator-rocket-heater.163878/

 

[paul wheaton]

I just found this thread. There are some links to my stuff earlier in this thread. I am not one of the top five brains in rocket mass heaters, but I think I might make the top ten list.

Here is my feeble attempt to answer some questions ...

> Do rocket mass heaters actually work or are they a temper mental nightmare?

They do work. I have one in my three bedroom house in montana. I heated my house last winter with 0.60 cords of wood (I measured VERY carefully last winter). I would usually go to bed with the house at 70 degrees and wake up to the house at 68 degrees. I would usually start a fire when it got to 66 degrees and stop feeding the fire when it got to 72 degrees. This was usually a 90 minute burn every other day. There were some sub-zero days where I would do a three hour burn every day.

> If they do work why are they not common?

I think there are hundreds of thousands of them in existence now. But that is just a guess.

I am surprised that people still buy any sort of wood stove when they could have a rocket mass heater.

> The problem is that it is a huge site built structure that really is not approved at all.

It is mostly a DIY sort of thing.

Approved in portland and ... last I heard ... about a dozen other cities. I've been told that a lot of insurance companies are coming around too.

The thing is that nine years ago they were pretty rough. But they have come a LONG way in the last few years. As of last year there is now an excellent book and ... I put out some DVDs, so my judgement of the DVDs would be very biased.

> they typically have small fireboxes that need lots of loading.

The batch box rocket mass heaters have really big fireboxes. The J-tube style has a super tiny firebox. The one in my house is a j-tube style - and it is smaller than average too. But as I said earlier, most of the winter I burn a 90 minute fire every other day. So I start the fire, go work in my office, go back every 20 minutes to add wood until I forget and the fire goes out.

I lived in a similar sized house with a conventional wood stove, and I remember feeding it a mountain of wood throughout the day on days where it wasn't all that cold outside. The loading of a rocket mass heater is a dream in comparison.

> are you going to want to stand there and feed wood in for a couple hours? Not me.

I don't know of anybody with a rocket mass heater that does that.

> Masonry heaters are much more effective and practical but either way you need a foundation for it and it will take up allot of space.

Rocket mass heaters have a lot in common with masonry heaters. Rocket mass heaters tend to heat a space with less wood, are built in a weekend (instead of three months) and cost a few hundred dollars (instead of $10,000 and up).

 

[paul wheaton]

> Who wants to looks at a rusty old barrel in they're house

I have a stainless steel barrel for mine. And I have seen people use a fabricated barrel shape. And we have a tiny cabin here with a rocket mass heater that is all masonry, no barrel or barrel-like thing.

> The stated advantage over conventional wood stoves is a fraction of the wood use.

Typically one tenth the wood. In other words, people that have replaced a conventional wood stove with a rocket mass heater have reported that they are more comfortable and are heating with one tenth the wood.

Some people choose to build a rocket mass heater that is designed more for "ease of use" than for efficiency, and they tend to get closer to one fifth or one eighth the wood.

> They have minimal heat lost to exhaust

Usually about 70 to 140 degrees F. Most conventional wood stoves are required by law to exhaust at 350 or higher. That's a lot of heat going outside.

> There is absolutely no inherent safety issue with the concept

Which will always be the case with anything new.

At the same time, the new book is quite excellent at covering safety. This makes for a wood heater that is far safer than a conventional wood stove. And one of the big reasons for that is that we burn so much less wood. While the house next door is burning all day, we burn for just an hour or two.


> What they claim and what you get in the real work are very different.

Really? I think we are really good about sharing our numbers. And I very, very carefully measured exactly how much wood I used last winter and what the indoor and outdoor temperatures were.

> And no matter how hot you burn that fire unless you keep the exhaust above the
> condensation point till it exits the house you will have creosote buildup. There is
> no way around it when burning wood.

Unless, of course, we have a way around it.

Most wood stoves burn at about 1000 degrees F. We shoot for temperatures over 1800 degrees F. Thus burning the creosote.

We insulate the burning area to force a much higher burn temperature, and THEN we harvest the heat.

Rocket mass heaters don't have creosote.

 

[paul wheaton]

> one potential problem with a rocket heater is back drafting on a windy day at the beginning and end of the fire.

I have not ever seen that problem. The barrel acts as a sort of upside-down hot-gasses p-trap.

> I could see the thermal mass issue being a problem with overheat or too long to heat up.

I have not experienced overheat, but there are cases where if you have been away for several days, it can take a while to get the mass hot. We can have an issue that we call "a cold plug" under the right conditions.

> If there is not an outside air source I could see someone turning on a bathroom fan or similar and reversing the draft.

Once my rocket mass heater is running, I have turned on the kitchen fan, both bathroom fans and the clothes dryer and it still runs hard in the correct direction.

Of course, if the mass is cold and I want to start the fire, and all four of those things are running - I can feel the air blowing the wrong way. Just as I have experienced the exact same problem with conventional wood stoves.

> My blazing success was a 'pocket rocket'.

Pocket rockets are pretty interesting. I now choose to never use them. The design of the pocket rocket typically results on the insides melting/burning/spalling out.

> J stoves with a 4" throat will not run dependably on cord wood no matter how small it is split

For a long time a lot of the pros said that 4 inch was a novelty for outdoors only. But now a lot of the issues have been resolved and people are creating some rather excellent 4 inch systems.