Homemade mass heater

This is my second year using a mass heater and I am still just amazed at how great a job it does! The heat is a whole different kind of heat. With the door open you still feel perfectly warm from the radiated low infrared heat. It looks like 1 cord of wood is going to last us 3 years! Now, we are in Texas, so winters are not cold. However, the old wood stove used 1 to 2 cords of wood every winter. I just stack 4 to 7 small sticks of wood in and light it up and our house is warm for 24 hours; even when its in the 20's outside. Its such a great heater I wanted to share what I did to make it. The cost was about $600. If I had it to do over again I would use a mix of our clay with sand in a ratio that gives 30% clay and skip the refractory cement all together. Heck, I might even skip the brick!

In climates like ours, where it can be 20 one day and 60 the next, the real trick is firing the stove with the right amount of wood and not firing the day before its going to be warm; unless of course you don't mind opening the windows and doors the next day

Starting the stove sometimes makes a little smoke unless I first light some paper and get a draft started. Once the stove heats up there is no viable some of any kind from the stack, on real cold days you can see some steam. The hot brick and insulated secondary burn tube make for a very complete combustion.

I choose the Russian bell design and sized it to provide the 24,000 btus of heat we needed.

I choose the Russian bell design because it does not involve complicated channel design to balance draft and heating efficiency. In this design heat rises and only the coolest part of the combustion gases exit the chamber, this maximizes heat absorption. The massive heater absorbs the heat of the burn and slowly releases it as infrared radiation over the next 24 hours. This direct heating makes it feel very warm even when the air temp is low; heating the air is not the way this heater works.


Double Bell Design. Heat rises, cooling gas falls, but it all is hotter than outside air so it rises/drafts upwards. The volume of the chambers allows gravity to move the gasses. Hottest gas is always retained.


There is a insulated secondary burn tube inserted above the first chamber.

First Chamber Bricked With Form in place to pour 3000F cement
¼ inch fiberglass board to allow for expansion of liner without cracking brickwork. Also, lets heat transfer slowly from hot liner to outside.

First Course Front View, cast high temp cement beam to prevent cracking of front


First Chamber Liner Poured/packed into form


Board Layed on form and sand is used to form a dome top for top of first chamber. Arch is stronger than a flat slab.


Second Chamber Lined/poured with forms removed, baffel framed and poured after chamber.


Second Chamber Bricked, with small oven door in side.


Small strips and loose boards used to hold top sand mold. No nails or screws, simple pull of support leg and it falls in for easy removal of form through small oven door in second chamber.


Second Chamber dome top formed with sand.


Third Chamber lined with clay sand mix; about 30 % clay. 1:1 local clay soil to sand. Cardboard now being used to create expansion joint..


The clay liner in the top chamber. Ran out of refractory cement.


Mixing More Clay and Sand For top Liner


Cheap Insulated pipe made from 8 inch galvanized duct pipe and 6 inch stove pipe wrapped in 1 inch high temp ceramic insulation. This was used for the chimney and this is a picture of the section used for the secondary combustion tube between the fire box and first “bell”.




Completed Stove

First Fire

Cool stove! You're making my life complicated though -- I'm going to be building a heater this year for next winter, and I've been going back and forth between a RMH and something like what you did here. Earlier today I was leaning more toward the RMH side, but now I'm not so sure again (I *really* want a functional oven to be part of the heater). It's a tough call.

How long did it take you to build it? Do you use the oven to cook very often?

I put in a clean-out door that is just wide enough to bake bread in. I wish I had the extra money at the time to put in a proper oven door. It really is nice to bake in hours after the fire has been out. I was hoping for more of a smoked flavor, but the stove burns so clean there is not really any smoke flavor, besides being to hot during firing... We bake bread when we have fresh wheat, but thats about it because the door is not wide enough. Otherwise I would use it all the time.

It took me about 20 days to build the stove.

Dan,

Nice brick work. (I come from a family of stone/brick masons.) Looks like you have some masonry skills.

Wonder if you ever tried a steal/metal version..?

I have some experience in building a J. Llopis ( pronounced Yo-pee )ovens and you have given me some great ideas, an oven could be incorporated into your design very easily..

Job..

Thanks for the complement, but I have only ever watched brick being layed before this project, lol. I just used a level and copied the hand a application motions I saw others use.

Thanks for the pictures, don't you hate that you can't learn what you'd change to make a new one until you got your first one built?

Looks nice, -Dan.

Yes, especially with something like this. However, even with the changes I wished I had made I still just adore this heater. If I ever build a new home I plan to build the heater into the foundation. If...

Oh, forgot to mention one other important thing I might change. A bypass slide damper would have eliminated the need to light paper to start a draft. I do not find it to be a big deal, but a bypass damper would make this a smokeless stove on cold starts; no smoke into house.

Wow, it is beautiful. I love it.

Did you use any books in your planning of this style?

I used only information from the internet mostly at russian site

Nice stove, Russian masonry stoves are lovely and pretty clean burning. Thanks for putting up the great photo essay.

Dan alan wrote:I used only information from the internet mostly at russian site

Can you post that link? I'm interested in seeing more on this.

Thanks

I have looked everywhere for the url, but I can't find it now; and that stinks because it covered sizing and BTUs as well as the benefits of free gas flow. If I do come across the link I will post it.

Hi, this is a very impressive masonry heater you've built. Thanks for posting the pictures etc. I'm just wondering what the temperature of the exhaust gas is, especially as the fire is nearly finished? And is the exhaust gas smoky at all? (i.e. does it compare to the rmh?) Thanks.

The exhaust gas is in the 80° range some time after start and the temperature rises as the liner warms up to about 200; depending on how much wood is burned. The outer brick never gets hot. There is some smoke on start up and once the fire is burning there is no visible smoke. On very cold days you can see steam; it does condense to water if you hold a mirror in it.

Dan alan wrote:The exhaust gas is in the 80° range some time after start and the temperature rises as the liner warms up to about 200; depending on how much wood is burned. The outer brick never gets hot. There is some smoke on start up and once the fire is burning there is no visible smoke. On very cold days you can see steam; it does condense to water if you hold a mirror in it.

Thanks for the answers, Dan. I presume that because you are in the US, 80° = 80°F (not 80°C)? So that would be from 26°C to 93°C. That's pretty good. Obviously the hotter the exhaust, the less efficient the heater is running.

How hot does the oven get I wonder (max temp)? I've been thinking about incorporating phase change materials (PCM) in mass heaters, and the setup you have is probably ideal for testing, though the wrong time of year in Texas probably. I can test the idea myself with a soda can and some candle wax in my own electric oven (i.e. how long does it take to melt and freeze again in a particular container), but it would be interesting to see the qualitative effects of a wax keeping the temperature at 60°C (140°F) until it all melts as far as keeping a house at a stable temperature and for longer (or with less volume of thermal mass).

One would have to guarantee that the temperature did not get near 370°C (700°F), the boiling point. There is also the flash point to consider, which is lower, perhaps 199°C (390°F). If I were building a heater incorporating this feature I would need to either make sure through enough testing that we would either stay below the flash point or with the addition of a non-flammable gas at the top of the container (e.g. nitrogen or CO2) and ensure that the temperature would not rise above the boiling point.

I've made another thread for this general exhaust temperature information, I'll put a link to this thread there.

Dan alan wrote:I have looked everywhere for the url, but I can't find it now; and that stinks because it covered sizing and BTUs as well as the benefits of free gas flow. If I do come across the link I will post it.

Hi Dan,

you might be refering to this website:
Kuznetsov's stoves
http://www.stove.ru/index.php?lng=1&rs=3

it's a tough read, but a lot of information, and years of experience!
The catalogues in particular are amazing IMO, with many stoves drawn brick by brick, layer by layer,

Cheers,

Géraud

Hi Dan. I've only just come across your stove build. Looks fantastic. I fancy building something very similar. I followed the link to the Russian stove building site, not easy reading.
Please tell me: did your design incorporate a secondary air supply, and if so, is it pre-heatedl? Did you include the gaps or crevices that I read about?
Love your stove, hope mine is somewhere near as good. Regards from the UK, Dave.

Hi.

I am interested in building a Kuznetsov 'free gas movement' stove, but think that two or more side-by-side bells are more efficient.
Doesn't the stacked bell design allow heat to convect, and thus to heat the top-most bell more? (the bell which should be the coolest) and only serves to warm up the exhaust more? If so, it is contrary in efficiency to two or more side-by-side bells, which give a closer to zero heat emission temp at exhaust, because the exhaust obviously gets cooler further away from the heat source.. (like bench mass storage design) I understand that stacked bells are better footprint-wise, and take up less horizontal space, of course.

I also have a new and very large firebox with pyrex side windows and pyrex front door, and fitted with a back water boiler. I had thought of incorporating this into the Kuznetsov design. Are there any disadvantages in using a steel stove with back boiler as a firebox? I have a reinforced concrete building, so mass and weight is not such a problem.

I intend having an insulated pipe exiting the firebox stove flue, with a drum above, as the rocket stove design.
The drum would sit 1.5" above the insulated flue pipe as does the rocket stove, and the drum would vent into a cavity which would lead to the first of the bells. Presumably an oil drum above would maximise burn temperatures, although I have not worked out how to extract fly-ash from the drum, as yet. (because it would be directly above the stove and behind two masonry walls. (outer cosmetic stone or brick leaf, and inner firebrick, with an expansion gap between the two))
Any suggestions or comments or ideas how to clean the drum and beneath it out? Vertical traps with access plates/doors below are probably not practical because of the width of the firebox/stove.

Scaled down side-by-side Kuznetsov 'free gas movement' bell systems could presumably work well with rocket technology, feeding into Chinese Kang-bed designs.

richie
bg

Ritchie B. : Welcome to permies.com, our sister site- richsoil.com, and a Big Welcome to the Rocket And wood stoves Forum Threads !

Unfortunately, any iron/steel in the combustion core (Burn Tunnel and Heat Riser) is doomed! The high temperatures that a Masonry heater ,Or RMH
burn at subject the metal to a host of problems, Notably High Temperature Hydrogen attack, and related Hydrogen embrittlement . This is a well
documented problem that is solved by not using iron/steel in those locations. It is possible to have a metal shell protected by Fire brick and Ceramic
Refractory insulation, Here it wood be better to find a masonry heater that meets your needs and build to spec !

Any exposure of the Hot Combustion gases to Temperatures below the ignition temperature of Creosote Famously 451dF, at temperatures around
250dF its vapors will settle out, collecting on the Heaters internal passages NOTE that this temperature is above the boiling point of water ! Any one
who thinks a RMH burns loudly has never heard a Creosote/chimney fire ! So the location of a boiler must be well planed for ( most of your fellow
Members will only use un-pressurized systems for safety with solid fuel fired Heaters ) Again it is a good idea to find a set of Masonry Plans and follow
the design very closely !

A Rocket stove does not have an 'insulated pipe' the heat riser, Only the current style Rocket Mass Heaters RMHs (with or without mass)! Current
recommendations would be a heat riser/ Barrel gap of 2'' for a 6'' system and more with an 8'' system !

Because of the high combustion Temps of ever the Rocket or the Masonry Heater, the ash produced is fly ash. A years fly ash production might be as
much as two loafs of store bought bread. A good yearly cleaning before the start of your heating season should be sufficient , following a well executed
design is the best way to have your clean out where it will work for you not against you !

In order to help you more clearly see the layout and benefits of the RMH system, and then clearly articulate your new ideas may I Recommend going
to :::--> Rocketstoves.Com for an instant download of PDF copies of the brand new 3rd edition of Rocket Mass Heaters this is ''The Book''

It will help you share and understand ideas/concepts of Your RMHs Size(s), Shape(s) and orientation to each other and the whole, and save you time
money and frustration ! - In Haste Big AL

Thanks for the valuable pointers Al.

I did want to make a Kuznetsov-type free gas movement stove incorporating my existing fire box, ( because I paid a lot of money for it ) but alas, if RMH's and Russian stoves do indeed get up to those temps, then I understand the non-feasibility of such a project
And better that I know now, than to do a lot of work and spend more money, and end up with problems ..and probably also ruin the firebox.

A great pity, because I've had the stove for about six years, and it's unused, and in addition, the bloody thing cost me 1,000 Euros.. Damn!!
Still, if I can get an efficient Russian heater design and build it, then I shall be happy, and possibly save that amount in wood over a few winters.

I have a wood burner pyramid-style design at the moment, a design which is typically Bulgarian, but now, in the autumn and also in spring, if I fire it up, it goes from being fairly cold (which is the reason I light it ) to severely roasting and unbearably hot after 15 minutes. Hence the idea for a Russian stove which would release gentle heat throughout the day and night.

Can anyone recommend anywhere that I can get any 'Dragon heater'-type plans, which would incorporate a RMH front end (with a vertical fuel feed to a 'J' tube) with a couple of Kuznetsov-type masonry bells for heat storage?
I have a lot of space that I need to heat, so a marriage of the two designs would be ideal.

thanks for any help and suggestions

ritchie

bg (Bulgaria)

Hi,

I'm really impressed with your heater. It seems much simpler than any masonry stove plans that I've seen and it makes it much more feasible as a DIY project.

I'd just like to know a little more about pouring the cement for the chambers. Can you tell me what product you used and where it might be available? I've only found small tubs of fire cement and it would take fifty or so of those! Did you mix it with sand/gravel? And what's the approximate thickness?

Can you also let me know in which part of the heater you would have installed the slide damper that you mentioned in a later comment? Would closeable vents in the door have the same effect?

Thanks!

A bypass damper would allow the gases to escape directly from the top of a bell to the chimney, without being forced back down first. Ideally, it would go from the top of the first bell to the chimney; you would need to plan routing in advance to allow this. Even inserting a damper in one or both bells to allow the gases to go straight through the top of the partition wall (as shown in one of the photos) would help.

If I knew about the rocket stove when I made this I would have incorporated it as the burn system.

Even so, this stove keeps providing amazing heat. The steel did burn out of the secondary burn tube, but the ceramic insulation became stiff and hold its shape and function without fail! It can be reached via the oven/clean out door.Secondary pre heated air is provided by a iron pile in the top of the burn chamber into the secondary burn tube, makes a nice wood gas flame! It should have been taller. It's not perfect, but we did not have floor space to waste. I think it is efficient enouy.

Basically you burn a fire and ALL the heat is absorbed. The core or chambers heat as high as 1100°F and by the. The exause it 200°F, but the burn is finished. In two hours the outer brick begins to warm up as heat slowly penetrates the fiberglass insulation board between the core and the brick. Outer heat reaches a peak in about 4--6 hours.

I like the vertical RMH concept.

There have been quite a few vertical bell style RMHs built and published. Search this forum and the forums at http://www.donkey32.proboards.com for threads on the subject. There are methods to calculate the best size of bell(s) for various systems.

Very nice build:) Thank you for posting this.

Another warm cozy winter finished up with mass heater!

Things I would do differently if doing it again..

I love the stove! One thing I would do differently is to spend them money to have a nice large oven door in the second chamber so that I could cook oak fired pizzas! Also, it very important to have 2 adjustable air inputs. One for the main fire chamber and another that goes through stainless steel tube and half way into the insulated secondary burn tune between the first and second chamber!! Last thing I would change is to put in a damper that allows bypassing the other chambers when lighting the fire. I happen to love the smell of wood smoke though..

The vertical design saves lots of space. I think I would use a rocket design for the fire next time and burn only 1 year old coppiced sticks. Currently, I let trees grow in a 3 year rotation. Every 3'rd year I coppice a section of trees in early spring and then let it regrow for 3 years to reach about 3.5-4 inches. After the 3'rd year the cycle starts again. I think using smaller stick fuel would allow a yearly cycle and less land for generating energy.

Beautiful project! Thanks for posting the details.

You answered one of my questions (how did the insulation hold up when the metal started to give out):

Dan alan wrote:If I knew about the rocket stove when I made this I would have incorporated it as the burn system.

Even so, this stove keeps providing amazing heat. The steel did burn out of the secondary burn tube, but the ceramic insulation became stiff and hold its shape and function without fail! It can be reached via the oven/clean out door.Secondary pre heated air is provided by a iron pile in the top of the burn chamber into the secondary burn tube, makes a nice wood gas flame! It should have been taller. It's not perfect, but we did not have floor space to waste. I think it is efficient enouy.
...

With the stub "secondary burn tube," I think you might be accidentally pretty close to a batch box rocket.

Might be you can get a little more clean burn with a "port," by retro-fitting inside the firebox a little. If you find compatible proportions.
Search "peterberg" "batch" "dimensions" "proboards.com" and you should find the current version of the tables. He let us put them in the back of our new book, too, the Rocket Mass Heater Builder's Guide.

The other question is, how do you like the refractory/clay liner after a year in use? I'd love an annual update, with some photos of how that fire box holds up, and anything else you try with it.

Depending on those firebox details, this might qualify for a beautiful-projects contest that I'm hoping to run, if our Kickstarter goes past the last stretch goal. Not much time left on it - see my signature for the link.

Thanks again for posting this very cool project! Nice to hear that it's saving you so much fuel - what would that be, 1/3 to 1/6 the wood?

-Erica

The fire box is holding up very well. 3000° refractory cement is tough stuff. However, when I do it again I will use local clay and sand mixed for about 30% total clay for the inside and outside. The insulation is a must in my opinion. It allows a very hot inner chamber that releases heat slowly to the outside. It gives a warm glow of heat that radiates for 24 hours.

It would be more efficient if I had a output damper at the top to stop all air flow through after the burn to stop heat from being drafted. It would then last more than 24 hours I think.

I ended up adding insulation against facing of door. I did not make a duel layer on the front where the door is. When the fire burns hot the expansion made a few cracks visible. If I had made the door area the same as the side it would have never been a problem. Non-the-less, it's solved now, but gets a bit fluffy from log rub on loading..

Also, notice how clean the liner looks clean. The fire burns very clean once it heats up.

Dan. How is your stove performing after a few winters ? Still just as pleased with it ?
Regards, David.

Dan.
Sorry to appear dim with what must have seemed a pointless question but for some reason your latest posts didn't appear until after I posted. I'm glad your stove is still performing so well. David.