Eric Moshier

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since Jun 27, 2013
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Recent posts by Eric Moshier

Yes, please feel free to contact me personally.
Eric Moshier
4 years ago

Satamax Antone wrote:Eric, thanks a lot for your reply.

About the "fact" that masonry heaters are more efficient than rocket mass heaters, i will have to disagree.

Don't get me wrong, I love what is being done with RMH, but when some of the people on these forums talk about figures & numbers that can't possibly add, that is when I get a little disgruntled.
The bullshit stops when you have real test data.

You can disagree, just look at the hard data and compare a masonry heater to any J tube style heater. Plus a large J-tube firebox is only 8"x8" so you cant get much wood into that space and you are only going to get up to ~7,000Btu's out of any given pound of wood and that is with a heater with around 80% overall efficiency. A typical well insulated home will require around 25Btu's per hr/ sq.ft. so a 1,000s.f. home will require ~25,000 Btu's/hr in Northern MN in January. That is 3.6#/hr or around 86#/24hr heating cycle. A J-tube with an 8x8" firebox will only hold about 12# of wood/fire so you would need to fire the RMH 7X to get the required amount of heat for a very small home.
This is what always seems to mystify the people who say you only burn 10% of the wood. Not Possible. There are only so many Btu's in a pound of wood and you can't magically get more our of it.

As people say; it all depends.

On the type of rocket core.

On the heat harvesting solution.

As far as heat harvesting goes, it all goes to the material that you use and yes dirt and soil is cheap but the density is severely lacking compared to brick and stone. The density is what stores the heat.

On the chimney behind.

It's sure that a cobbled up J tube, with a bench with tubes can seem very inefficient. Tho, some testing done by Peter Van Den Berg, has proven the J tube to be a very capable contender on the efficiency side. Still a fair bit of excess air. But the numbers are real good.
Peter is doing some wonderful work with his batch burner, but he is basically turning the rocket stove into a masonry heater. The excess air is what kills your efficiency numbers.

And if you can beat the CO readings of a J tube, with a masonry heater, you are very skilled.

Unless you are building your fireboxes with 100% underfire air like we did 30+ yrs ago the majority of all masonry heaters built with the Eco-Firebox have CO numbers of ~ .04-.08. This firebox is now the only firebox that can be built in Germany, Austria, France..

The bench and horizontal tubes, i'm not too keen on. I will agree with you, on the fact that there is better heat exchangers and accumulators. But it soo cheap that it makes it worthwile.
The bench is fine if you have a lot of floor space, like 4'x8' with a typical RMH. A standard masonry heater has a footprint of ~2.5' x 4' w x 7' h.

I will add that there's no money to gain here. Most of the rocket builders are here to save money, no to spend any.

I wasn't trying to sell anything here, just dis spell some of the myths that were being thrown around about masonry heaters. I think it is great that with around 90 firebrick and a 55gal. drum that you can make a RMH, add on 3'x6' of heated bed with metal chimney pipe and lots of clay,rock,& sand and you have a decent heating system.
You can also build a simple double bell heater, or even a contralflow heater with around 300 firebrick (~$500) and 200# of refractory mortar ($150) or just clay mortar (which is not technically legal). You can finish the outside of the heater with the same cob/adobe that you build a RMH with or buy ~90-4" solid concrete block ($140 with mortar), or local stone, or reclaimed brick... for free. Use and old fireplace door or buy a new one for $200+. Yes a little bit more educating is involved with laying stone or brick but when you are finished you will have a heater that will work 99.9% of the time and it will have a firebox large enough to shoot out around 360,000Btu's on 1 fire and last 100+ yrs before needing the firebox rebuilt. Plus is sits in a 3'x4' space in your house not a 4'x8'.
Another bonus is that a masonry heater is listed in the IRC so you can legally build them and your insurance company will cover them.
A smaller masonry heater for heating ~1,000s.f. normally only needs 200 firebrick.

When you say, 1000 dols to make a masonry heater. Let me doubt it. It's your job obviously. But If i have read some of the MHA papers correctly, for a long flywheel mass heater. You often hear about 5 or 6 tons of firebricks. Let say, 1700 bricks, that's already a fair chunk of money to shed upfront. I have seen some of your pebble stoves. That would make it cheaper. But there is the concrete problem comming into play in this case. Which is not realy that green a material. And costs a bit too, compared to cheap as dirt cob.

The facts are above and I have built over 300 heaters. I built one monster triple bell heater that was 16' tall but there were only ~1,500 firebricks, I have never seen one to take 1,700 and I have seen a lot of heater building plans. A normal heater will take ~ 300 firebrick.
There might be some monster Russian heaters that are 3'x8'x7'h but almost no one builds those old inefficient styles anymore.

And, then, when you delve into Batch rockets, and bells. I realy doubt any conventional mass heater would compete with the evenness of the burn, and it's efficiency.
Look at the data. J-tubes don't come close,too much excess air. Peters batch box is very good, but to me it is more of a masonry heater hybrid than a RMH. Horizontal firebox, fed into a vertical channel which goes into a Bell or more channels. Yup, sounds kinda like a masonry heater.

You keep thinking that Peters batch firebox with a Bell is not a masonry heater. Why, just because he uses an insulated firetube (that is very expensive) and then Bells/chambers (Just like a Bell Heater). He is getting close to the same numbers that we have been getting for years. Plus it looks an awful lot like a masonry heater.
Normally if it walks like a duck & quacks like a duck..

I agree, for the most part, batch rocket mass heaters are just a smidge different. The core or engine not being a simple firebox, with added air channels.
Peters batch box with added air channels is basically turning into a masonry heater, just Peters version of one. Peter is doing some great work, I like him very much.

I would like to convince you.

I know the design, testing and data behind all 3 units here (J-tube, batch box, & masonry heater). Once the data hits the table all the BS stops. It's hard to argue with hard data.

Great conversation by the way. I am just here giving the real facts about the other side of the story (masonry heaters). I used to teach rocket stove building workshops, I just didn't like making up excuses for why they legally couldn't be built in most area's because there is no ASTM for them and they are not in the IRC so officials have issues with them. Plus they are still kinda experimental and will smoke back on you on the wrong day. A properly designed and constructed masonry heater will never smoke back on you once the draft is established. Yes, some clients might get some smoke back in the beginning of a fire IF they did not have the draft originally established. If you are having a fire 1x per day you should never have any issues with draft unless the temperature differential from outside to inside is not that great. Your not going to get a great draft if the inside temperature in 68º and your outside is 50º. Once a fire is going in a MH you should never get any smoke back if it was designed properly.
4 years ago
Here is our current list of workshops that we are teaching at the North House Folk School in Grand Marais MN for this winter. Both of them are 90% full so reserve early if you are interested in taking a class.

Here is the link to the Winter Masonry Mass Heater classes that are being offered.

North House Folk School - Courses, Classes, Workshops

North House Folk School - Courses, Classes, Workshops
Eric Moshier Masonry heaters originated in Northern Europe where winters were cold and fuel wasn’t always plentiful. The natural response?

View on

Masonry Heater Association annual meeting workshop listings
I will be teaching a fairly simple Russian Bell Heater/cookstove combination stove at the MHA annual meeting in April in North Carolina and again at the North House Folk School in May. Here are the links for both of those workshops:
MHA The agenda of workshops is not finalized yet. Last year PeterVan ,Donkey, & Lasse Holms were at our annual meeting discussing current RMH technology.

Here is the May 4-6 Bell Heater/cookstove combo workshop link. This has not posted yet but will in a few days. Its brand new.

Email me directly if you have any questions at or visit our website for future workshops at
We are now manufacturing RMH doors for batch burning fireboxes
4 years ago

Nathaniel Rogers wrote:Hi Mike,

Thanks for all of the input and information. I'll have to spend some time doing research into bell designs and factoring that into my decision. I am similarly more inclined towards a masonry heater for the aesthetics and decreased need for frequent burns. The cost was putting me off, but your info has changed that factor. Down in NC I do have less of an issue with more frequent burns as I wouldn't be running the heater as many days, or for as many hours a day as you would in Michigan. I also have to look into what my local building office will allow me to get a permit for. I look forward to your future posts about your project on Permies.


That Lopez Labs page is awesome. That is some fantastic data on various configurations.

Hello Satamax,

If you are going to invest 2-7+ days of your time, money and energy building a reliable, safe heating system for your home and family you are better off building a masonry heater. They have been in use for around 1,000 yrs and they work 99.9% of the time without any issues as long as they are built according to a set of plans that has been trial tested by experienced masonry heater builders and not just weekend pyro's. Any masonry heater that is properly built will out live the builder and most likely the next 5 generations. Yes, they might take a day or 2 longer to build than your typical rocket stove and cost you $500-$1,000+ dollars in materials but you are building something that will last potentially 100's of years. There is considerable testing that has been done and is still being done on masonry heaters in North America and in Europe and they have proven to be safe and work 99-100% of the time and not be temperamental like a rocket stove can be at times. Masonry Heaters are also listed in the International Residential Building Code so they can legally be built anywhere that they allow wood burning. Since they are listed in the IRBC and if built according to ASTM 1602 then the majority of all insurance companies will also cover them being built in your home. Yes there are kits and systems for building masonry heaters that will cost from ~ $1,000-$7,000 but all of these systems are guaranteed to work if built properly. As far as testing and efficiency of a masonry heater goes compared to a RMH just go onto the Lopez Labs page to see some of the work that Norbert and the rest of us have done testing masonry heaters. The Europeans have 1,000s of tests done especially on Kachelofens.
Rocket Mass Heaters are still deemed experimental.

Not all masonry heaters are that difficult to build, yes the require some gluing together of firebricks but so do RMH's. There are simple Russian Bell Heater plans that will outperform any RMH in performance and longevity, yes they might take a day or 2 longer to build and cost you a few hundred dollars more but in the long run they will outlast and out perform and you wont have to tear it apart and rebuild it in the next 100 yrs.

Don't just build something because it is cheap and fast. You are only given so much time on this earth that you will never get back. Choose wisely.
Eric Moshier
4 years ago
The Milan Village Arts School has the opportunity to add a new class for this summer. Eric Moshier is a regular instructor at North House Folk School in Grand Marais and will be traveling to Granite Falls in early June to construct a masonry heater at Scott Wilson's new straw bale home. A masonry heater is highly efficient and can be used for heating as well as baking and heating water. A masonry wood stove would be a great asset to any Minnesota home.

As this is an actual build, student hands on participation is limited, but the knowledge you will gain is extensive and valuable.

The build will occur from June 2 to June 6. The first 2 days is the core build and the second 2 days is the finishing work. Most of the build should be finished by the 6th. Students can register by the day. It is not necessary to be present all 4 days.

The tuition is $50/day. As this is a special class, the tuition is the same for members and non-members.

Location: The workshop would be held at Scott Wilson's building site (9085 5th Avenue, Granite Falls),
Next to the old Swensson farm outside of Montevideo.

Eric's classes are highly sort after and always have waiting lists. This is a terrific opportunity to learn about masonry heater building at a very special price.

Please contact the Milan Village Arts School to register for this class.

Masonry Heater Building

with Eric Moshier

Masonry heaters originated in Northern Europe where winters were cold and fuel wasn’t always plentiful. The natural response? Create a wood-fired presence that was at once incredibly efficient and highly attractive, capable of generating abundant heat and ideal for cooking/baking. Masonry heaters are built with fire bricks and utilize their high mass to radiate heat for 12 - 24 hours, a feature which means they only need to be fired once or twice per day. Students will experience and discuss heater design, sizing options, brick selection, oven integration, door and hardware installation, code considerations, and tool use. An exterior finish of clay brick will be utilized. Stucco and clay plaster options will be discussed, as will larger heaters capable of heating spaces up to 2,500 sq. ft.
The history of masonry heaters can be traced back 1,000 years or more. Beautiful and highly functional, they are built near the heart of a home where their solid and warm presence serves as an ideal gathering point. Design flexibility of masonry heaters enable them to be part of homes of many sizes and incorporate features such as heated benches, baking ovens, or heating domestic hot water.
This heater workshop will be built on site at a clients house as more of an introduction to masonry heaters. Due to the time restrictions on this build there will be very little hands on experience but you will be able to watch the entire build and ask questions as we are building the heater. We will be building a German style Grundofen heater with a heated bench and a black oven. We will finish the heater with clay brick and clay plaster.

Eric Moshier

Duluth, MN
Eric is a third generation stone mason who has over 25 years of experience. As the owner of Solid Rock Masonry in Duluth, he has built Finnish, Swedish, Russian and German style masonry heaters throughout the Midwest and southern Ontario. A long-time member of the Masonry Heaters Association, he has led numerous workshops across the Great Lakes Region and at the MHA annual gathering. To compliment his strong desire to educate people about heating with wood in efficient and beautiful ways, Eric has pursued projects ranging from coaching hockey to building log homes to being an environmental consultant.

If you no longer wish to be on our email list, please reply and ask to be removed.

Ron Porep
Milan Village Arts School
P.O. Box 230
Milan, Minnesota 56262
(320) 734 4807

Office Hours:
Wednesday & Friday, 10 a.m - 4 p.m.

6 years ago

I will be teaching 2 masonry heater building workshops in the next month.
The first one will be a J-loop with an 18x18" firebox, a black oven and a heated bench. This heater will be built down in Altura MN which is in the SE corner of MN. The dates for this build are July 30 - Aug.1. This first workshop will be mainly hands on. Contact me directly for information. 218-343-2978

The second workshop will be up at the North House Folk School up in Grand Marais MN on Lake Superior. The dates for this workshop are Aug. 15-18. We also have 2 other workshops scheduled for this winter at NHFS. Here is the link to the classes.

I am also trying to plan another rocket stove building class and a masonry cookstove building class at the NHFS. Please email me if you want to be added onto my list for future workshops.
7 years ago
We have a 4 month old female mangalitsa hog that is foaming at the mouth and vomiting. She doesn't want to eat or drink. Her stools seem formed and normal.
Any help or advice would be much appreciated.
7 years ago