Why dont we all want rocket mass heaters?

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electrathon

Minister of Fire
Sep 17, 2015
571
Gresham, OR
I have wondered this for some time. I just saw a rocket stove (different than a rocket mass heater, but similar) pic posted in another thread and figured I would ask the question.

Do rocket mass heaters actually work or are they a temper mental nightmare? If they do work why are they not common? I do not see them talked about often here, is there a reason? People afraid of the inside the house fire going to burn your house down? Too long to get them to temperature? Not enough firewood consumed? Just looking for input.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,187
central pa
Do rocket mass heaters actually work or are they a temper mental nightmare?
By rocket mass heaters are you talking about the european style masonry heaters?
 

electrathon

Minister of Fire
Sep 17, 2015
571
Gresham, OR
By rocket mass heaters are you talking about the european style masonry heaters?
Sort of. They look to me to get lit off and work as a blast furnace, allowing the draft to run the fire very, very hot. Think of a constant rush of a chimney fire. They burn small wood, and just feed off the end of the pieces as they burn. https://richsoil.com/rocket-stove-mass-heater.jsp There is usually mass around them, gravel, clay, etc that heats, then you let the stove go out after an hour or two and the thermal mass radiates.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,187
central pa
nevermind i just looked up the term and yeah I know what they are. The problem is that it is a huge site built structure that really is not approved at all. They can be safe but no inspector or insurance company is going to know what to make of them. Also they typically have small fireboxes that need lots of loading. Yes you only burn them a few hours a day if it is sized right for your house but are you going to want to stand there and feed wood in for a couple hours? Not me. 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.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,187
central pa
Who wants to looks at a rusty old barrel in they're house
They dont have to have the barrel visible or even use a barrel. There is a very nice looking one in a cool earth sheltered home that we work in. But they dont use it they had us install a traditional wood stove instead they said it is much easier to use.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
26,187
central pa
We do, but you know who won't like it.
Why would you want one of them over a traditional wood stove or a masonry heater? They do work but they take all but constant feeding while you are burning. If they were more user friendly there would be groups designing them and getting the designs approved like the masonry heater association. There just is not enough demand.
 
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jatoxico

Minister of Fire
Aug 8, 2011
4,355
Long Island NY
Why would you want one of them over a traditional wood stove or a masonry heater?

Wasn't really a serious comment holler. They are cool but not very practical as you outlined.
 

electrathon

Minister of Fire
Sep 17, 2015
571
Gresham, OR
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.
 

electrathon

Minister of Fire
Sep 17, 2015
571
Gresham, OR
Why would you want one of them over a traditional wood stove or a masonry heater? They do work but they take all but constant feeding while you are burning. If they were more user friendly there would be groups designing them and getting the designs approved like the masonry heater association. There just is not enough demand.
There are groups designing them and they are being approved, that was why I was questioning why they are not more talked about here. The stated advantage over conventional wood stoves is a fraction of the wood use. They have minimal heat lost to exhaust, kind of like a pellet stove exhaust..
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,187
central pa
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.
The problem is what standard are they built to to ensure they are safe? They are site designed and built they are only as safe as the person building it makes them. The same goes for an open fireplace but the dig difference is that there is a standard to build to to ensure you have proper thicknesses and clearances. There is absolutely no inherent safety issue with the concept but there is allot of room for major safety issues.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,187
central pa
The stated advantage over conventional wood stoves is a fraction of the wood use. They have minimal heat lost to exhaust, kind of like a pellet stove exhaust..
Yeah according to the guys promoting them. What they claim and what you get in the real work are very different. 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.
 

electrathon

Minister of Fire
Sep 17, 2015
571
Gresham, OR
Who wants to looks at a rusty old barrel in they're house


Sent from my iPhone using Tapatalk
they do not have to be a rusty barrel. They can be stainless, can be rolled steel, etc. This is sort of like saying we do not want a wood stove in the house because they are made out of rusty barrels. They can be, but they can be made from other things too.
 

branchburner

Minister of Fire
Sep 27, 2008
2,758
southern NH
I do not see them talked about often here, is there a reason? People afraid of the inside the house fire going to burn your house down?

Like bholler says... code and insurance. I'm sure more DIYers would consider them if it weren't for that.
 

electrathon

Minister of Fire
Sep 17, 2015
571
Gresham, OR
Yeah according to the guys promoting them. What they claim and what you get in the real work are very different. 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.
That was what I was wondering. What the real world issues were compared to the people talking of them. I do know that it is possible to burn a wood fire so that there is less/little creosote build up. I have not cleaned my shop stove ever in 25 years and there is zero build up (I check every so often). Also some stoves burn clean, some dirty, I suppose it is possible that they are burning clean.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
26,187
central pa
. I do know that it is possible to burn a wood fire so that there is less/little creosote build up. I have not cleaned my shop stove ever in 25 years and there is zero build up (I check every so often). Also some stoves burn clean, some dirty, I suppose it is possible that they are burning clean.
Yes your stack is clean because you are putting enough heat up the stack to carry it all out. When burning wood the exhaust temps need to stay above the condensation point so basically above 220 till it exits the chimney.
 

electrathon

Minister of Fire
Sep 17, 2015
571
Gresham, OR
I have no idea what we are talking about...but I love the idea of saying I have a rocket stove.
I have to agree. If you renamed it a candle flame heater it would be far less appealing. Kind of like calling an older woodstove a smoke dragon, like a racial slur for stoves. We don't necessarily know that they are bad stoves, just that they have not joined into the EPA club many of us now live in. Rocket mass heater sounds like an awesome wood burner.
 

peakbagger

Minister of Fire
Jul 11, 2008
6,625
Northern NH
Take a look at a Jetstream or Dicks Hills design, Its basically rocket mass heater with much large capability to heat a large thermal mass as it has an external storage tank. Incredibly clean burn and super efficient. .
 

ddddddden

Minister of Fire
Oct 20, 2009
1,487
Central Va
Here's your rocket stove forum.
https://permies.com/mobile/f/125/rocket-stoves

I guess we're not cööl enough to have a röcket forum.==c

But yeah, as you noted, hundreds of lbs isn't going to get it done. You need thousands of lbs of thermal mass to capture enough heat to keep a house comfortable for a day after the fire is out. Unless they're building a sod house, I agree that most folks looking for this kind of heat would go with a traditional masonry heater, which burns the inferno in a proper firebox and captures the heat in a convoluted exhaust path.

https://en.m.wikipedia.org/wiki/Masonry_heater
 
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iamlucky13

Minister of Fire
Jan 27, 2015
652
Western Washington
I hadn't seen this variation on a rocket stove before, but looking at it, it does make sense as a scaled up and improved rocket design.

I'm not really convinced they outperform the better firebox stoves and avoid the potential for creosote issues, and the installation planning seems like it would be far more complicated.

I also see a lot of utterly absurd claims being made about them. The first site I found claimed 10x the efficiency of a 75% rate woodstove. Even they knew that was an absurd claim, though, and qualified it in their FAQ's, concluding that aside from laboratory conditions, "An excellent operator might be able to get about 35% efficiency. Most people run their '75% efficient wood stove' at 3% to 15% efficiency."

That's interesting then, because by my calcs, at 30 degrees outside temperature, I should need to be burning somewhere between 200 pounds if I'm an "excellent operator" and 2250 pounds of wood per day to keep the house at 70 degrees. I've never tried to weigh my use, but I seriously doubt I've ever exceeded 100 pounds, which based on my estimated heat loss would be in the ballpark of 70% efficiency.

I'd love to know who they found who was burning over 1/2 a cord per day!
 

byQ

Minister of Fire
May 12, 2013
529
Idaho
Hi electrathon, I'm in Idaho but have spent most of my life in Oregon. I just built a big masonry heater, https://www.hearth.com/talk/threads/mh-puzzling-together.155464/#post-2089184.

I think the attraction to rocket/rocket mass heaters is that someone can build one themselves, and do it cheaply. Masonry heaters scare do-it-yourselfers due to their perceived complexity and cost. I know there are some masonry heater builders who are delving into rocket mass heaters because many people are interested in them. It all starts with a coffee can and takes off from there.

In your area a class is taught in Eugene by Max Edleson http://www.firespeaking.com/

Another masonry heater builder teaches a class on RMH's in Minnesota, Eric Moshier http://solidrockmasonry.com/. He says masonry heaters are far superior - they burn hotter, less fuss, and are more durable. But there is an interest in rocket heaters so he teaches a class.

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......
 
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electrathon

Minister of Fire
Sep 17, 2015
571
Gresham, OR
.
https://www.hearth.com/talk/threads/mh-puzzling-together.155464/#post-2089184
...

In your area a class is taught in Eugene by Max Edleson http://www.firespeaking.com/
...

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.