by Gianni on our previous farm

The Breakdown:
Fire Burns Sideways
Fire Burns Twice
1-Wood Burns in Combustion Chamber
2-Gas Burns in Burn Barrel
Exit Fumes Heat Mass
Mass Radiates Heat

our mass includes 3 55 gallon barrels of vegetable oil

The Details:
The Rocket Mass Heater is designed to burn small pieces of wood cleanly for a few hours each day.  It stores this heat in the mass of rock, earth and in our case vegetable oil that the exhaust pipe travels through on it's way to the outdoors.   The bench of mass will be used over the winter to heat butts and keep the entire greenhouse above freezing.  In the spring the tile bench and pallet shelves will hold our sprouting seeds and seedlings; which is why our new potting station is right next to the RMH.  For the first firing of the season the RMH will burn constantly for a day (or 2) in order to heat and dry the newly formed mass.  After the initial firing, just a few hours a day should keep the mass hot.  Because of the high rate of efficiency of the burn and all that mass soaking up the heat; the final exhaust coming from the chimney pipe is only slightly warmer than outdoor temperatures and is mostly steam. 

The RMH is a little tricky to get going.  A small chimney primer fire is started in the bottom of the chimney pipe by opening the end of the T section and placing a lit fire starting brick inside.  By closing the T with the primer fire burning the heat creates the proper drafting of the air through the system.  Then placing another fire starting brick in the main burn chamber of the RMH; followed by paper, tinder, twigs and sticks the fire will mostly manage itself Once The Flames Are Consistently Traveling the Correct Direction Through The System.   The burn chamber is cleaned by hand after each firing and the the entire exhaust pipe can be sucked out through the T in the chimney once per year.

Do a little searching and you'll find that Rocket Mass Heaters can be made to be very elegant and are being used for all sorts of applications; in homes, cabins and for aquaponics not just for greenhouses.