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”.
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.
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.
Joined: Feb 16, 2012
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...
Joined: Feb 16, 2012
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.
Joined: Oct 16, 2009
Location: Tonasket washington
Nice stove, Russian masonry stoves are lovely and pretty clean burning. Thanks for putting up the great photo essay.
Need more info?
Ernie and Erica
Wood burning stoves, Rocket Mass Heaters, DIY,
Stove plans, Boat plans, General permiculture information, Arts and crafts, Fire science, Find it at www.ernieanderica.info
Joined: Aug 29, 2009
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.
Joined: Feb 16, 2012
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.
Joined: Feb 16, 2012
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.
Joined: May 02, 2013
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.