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Rocket Mass Heater – an Eco-friendly Stove Build Tutorial


FZRXUUVHR9V7OVS.MEDIUMA lot has been said about Rocket Mass Heaters, and their ability to cheaply and efficiently heat up entire houses.

If there is an option to heat up a home for a fraction of the sum, which the owners are spending on right now, it is definitely worth exploring. In fact, it is not difficult to achieve this, and the solution is a Rocket Mass Heater. Here is a short and very effective tutorial that can show you how to build one yourself.

They have numerous advantages over standard wood-burning stoves, including maintaining warmth for much longer, and not being restricted to type and condition of burning material.

Reading through user experience and feedback, including that of the provider of the original tutorial on the Instructables, user velacreations, it becomes clear that the gain from a DIY Rocket Mass Heater (RMH) is much larger than the investment. In fact, the only disadvantages would be the amount of work you have to put into building it, and the missing convenience of being able to just go and pick a ready-made one from the store.

So, here is the tutorial. The result will be a fully functioning, self contained RMH, which can be easily disassembled if needed. It guarantees to provide you with super cheap and efficient heating, which is not only better for your wallet but for the environment too.

Materials and Equipment

FI98JWKHR9V7ORU.MEDIUMTo build the Rocket Mass Heater you will need to get the following materials:

  • 26 gauge sheet metal with the following dimensions: 48” x 18″, 16” x 109”, 20” x 89”, 41’ X 36”
  • 16 gauge sheet metal with the following dimensions: 31” x 14”, 32” x 40”, 33 ½” x 43″, 34” x 34”
  • 20 ft. long 1″ square tubing
  • 6″, quarter of an in thick well casing pipe
  • Stovepipe and elbow
  • Perlite and Sand
  • Half in sheet metal screws
  • Fire bricks and regular bricks
  • High temperature resistant silicon and paint

You will also need the following equipment:

  • Tin snips
  • Pliers
  • Plumb bob
  • Clamps
  • Saw, with both metal and masonry blades
  • Hammer
  • Drill
  • Welding machine
  • Tape measure and a marker
  • Heat resistant, non-flammable clothes, gloves and goggles


Step 1. Building the base

FKF444XHR9V7OO9.MEDIUMThis step is needed in order to contain the sand, which in this case is used as a thermal mass.

To build the base, you need to cut a piece of the 26 gauge sheet metal. The size of the piece should be 1 inch bigger (on all sides) than the space where you want to fit the unit. If you would like to stick to the “done and tested” version, then you would need a 46” x 18” (48” x 20” including the 1” flap) cut out. Using the marker pen, draw an outline that indicates the 1″.

Then, with the snips, cut from each corner into the drawn line and then bend the flaps upwards using the pliers, so that they can be bolted to the wall. Cut the flap at the place where the ash box will slip in. Again, if you would like to stick to the tested design, then the 6 and a half inch wide ash box will start at 6 and a quarter inch from the left front corner.

The last thing to do here is to put the base in place, and mark the metal where the stove points down. You can do this easier by hanging a plumb bob from the center. Draw a circle with a diameter of the size of your stovepipe.

Step 2. Building the frame

FJDI0X2HR9V7OOI.MEDIUMThis is one of the crucial steps, as the frame would hold the walls of your RMH. Here you will need some good welding skills, and suitable protective gear. If you are not an experienced welder, it might not be a bad idea to call a specialist to guide you or at least supervise what you do. In any case, even if a welder is not available, make sure that you are not alone there, just in case.

Here it is very important to get the measurements right. Before we continue with putting it all together, here are the lengths of the cuts of square tubing that you will need to prepare: 15”, 15”, 16”, 36 ½”, 19”, 34”, 34”, 28”, 19”, 8 ½”, 7 ½” and 7 ½”, making a total of 20 ft, or one piece of tubing.

Please do refer to the picture at all times along the way. Building of the frame is quite difficult to describe in writing, so it could get a bit confusing at times.

The two left-hand upright pieces of metal should be 15″ tall, the piece that connects them is 16″. A horizontal, 36 and a half inch square tubing piece run horizontally, and it is welded between the 34 ” left-hand upright and right-hand upright pieces.  Measure 13″ from the left-hand edge of the 37″ horizontal piece, and mark the spot. To the right of this mark weld another 19″ piece.

For the front part of the frame, you will need to weld a 28″ piece horizontally between the front, left-hand upright and the front right-hand upright. Then weld a 19″ piece between the right-hand uprights, at the top. Then, make a frame around the ashtray opening by welding two 7 and a half inch vertical, and one 8 and a half inch horizontal  pieces.

Once all is done, place the frame inside the base piece of metal.

Step 3. Apply the first layer of metal

FR0CMBHHR9V7OP6.MEDIUMThe first layer of metal covers the fire box area. It will be a cut out from the 26 gauge sheet metal with a total parameter of 16 “plus extra 1″ (which again should be marked using the marker pen).

Using the hammer, bend the 1” part until it reaches 90 degree angle to the rest of the sheet. Then fit the bend part to the back left-hand upright of the frame, with the remaining sheet metal going towards the front left upright part. Screw the metal into the left-hand edge of the back upright and the side of the front upright parts of the frame, and bend it around.

F0X91KLHR9V7OPJ.LARGEOnce this is done, cut the opening for the ashtray along the bottom edge- just as before, 6 and a quarter inch from the front left corner, cut a rectangular shaped part- 7 and a half in tall, 6 and a half inch wide.

Then, bend the metal around the curve, and once you reach the starting point, screw the end. Screw the bottom of the sheet to the base, by placing an individual screw every 4″. Place the ashtray frame on the inside of the unit, and also screw it to the metal sheet.

The last step is to apply a bead of silicon around the base and over the seams.

Step 4. Apply the second layer of metal

FAWBZBKHR9V7OQY.MEDIUMCut a 20″ wide and 89″ tall piece of the sheet metal. Fit one end of the sheet in between two pieces of square tubing, leaving 1″ to hang over the edge. Hammer the 1″ flap until it is positioned at 90 degrees.

Place the 1″ flap left side of the back left upright, with the rest of the metal running right along the back, then screw in the back side. Following the shape of the first layer, and screw it to each upright part of the frame. This time, when you reach the starting point to not screw it right away. Paint the unit, and place it in its chosen location, aligned with the stovepipe.

Step 5. Add the stovepipe

FBLSW4IHR9V7ORG.MEDIUM (1)Connect all the pieces of stovepipe together so that they go all the way to the bottom of the unit, where it should end in an elbow pointing towards the left. Cover the stovepipe with a piece of 26 gouge sheet metal (41″x 36″ if you’re following the demo design). If you leave part of the pipe uncovered, you allow for some fast direct heat.

Once this is all done, paint the metal.

Step 6. Make the ash box

F0S0SFQHR9V7ORI.MEDIUMConsidering what you have made so far, this should not be a difficult step to go over. Cut three pieces of metal from the 16 gouge metal sheet, with dimensions 14″ x 6″ and two with dimensions 6″ x 7″.

Weld the pieces together to form a drawer-like box, place a handle and paint it over with the paint. Then place it in the opening.


Step 7. Make the grill

F9E54LEHR9V7ORT.MEDIUMThis is also a pretty straight forward step. Cut a 7” x 7” piece of 16 gauge or thicker metal.
Mark a grid on the metal, and then drill a quarter of an inch hole at each intersection.




Step 8. Place the bricks

FU6PUGAHR9V7OS8.MEDIUMThis is also another stage where you should refer to the photos at all times. The ultimate goal is to create a path for the smoke, and to retain the sand.

First, stack bricks on both sides of the elbow of the stovepipe, making sure the end of it is still exposed. Then, put sand in the back corner, around the stovepipe and behind the bricks.

Leaving 6″ wide gap in between the end of the stovepipe elbow, stack bricks until you reach 8″ height. Leave some space between the bricks (roughly around quarter of an inch) and do not forget to leave the opening for the ashtray free. Once this is done, place the grill on top of this construction, in the center of the firebox area.

FS96QBCHR9V7OSJ.LARGEThe last part here is to make a box on top of the 8″ level, starting from the right side of the grill, going all the way to the 6″ from the stovepipe. The box should be 7″ tall and have a roof. Fill in the gaps with sand.




Step 9. Make the heat riser

FBKU32QHR9V7OSQ.MEDIUMOne last push left. This one is the most detrimental part of the whole construction process. Getting it right guarantees you complete combustion and the much-desired results.

So, take the 6″ casing pipe, which should be 32″ long, and place it on top of the brick roof, at the end of the stovepipe. Mark the bricks, and cut out the inside of the circle. Ensure that you cut on the inside of the mark so that there is space for the pipe to sit on the bricks over the whole.

Then take a 32″ tall, 40″ wide piece of the 16 gauge metal, and bend it to make a 32″tall tube. Screw it around the pipe, and the space between the two fill with carefully packed perlite.

Next you need to make a barrel. Cut a 33 and a half inch by 42 inch piece of the 16 gauge metal and bend it until it overlaps by 1″, then screw it. Make a lid and weld it to the barrel, then wait to cool and paint over. This you can use for cooking if you like, it gets very hot.

FVIE7H7HR9V7OVL.MEDIUMNow, place the new barrel over the perlite one, leaving the right edge to hand over the bricks. Then place bricks to protect the gap between this barrel and the stovepipe and fill with sand.

Also, the remaining loose flap from Step 4, you can now bend around and screw into the upright. Then fill u this level and the stovepipe’s barrel with sand up to the top. You can expect that in about a week, this will sink down about an inch, which you can fill with pebbles (for prettier appearance).

Step 10. Finishing touches

FL3TGF5HR9V7OVZ.MEDIUMTo finish the job, place a layer of bricks around the firebox, making sure that you fit them well, and you cut them so that they look good.

Then, only the tests are left. Place some burning material on the grill, light it up and add more once it is burning.

If it is all working properly, there should not be any smoke or flame coming out the top of the box. If there is smoke, you can push the burning material a bit further in to heat up the riser and help the initiation of the draft.

Well done! That is it!

Now, if you think that you would require some more guidance and face-to-face tutorial, I would like to point you to a currently ongoing Kickstarter campeign. The guys offer a series of DVDs (or an ebook) that include detailed tutorials and workshops on how to safely construct a fully functioning, and fancy, RMH. The campaign seems to be gaining quite a bit of popularity, almost having reached their target with more than 20 days to go.

So, yes, you have many options, and zero excuses not to start saving money on heating and reduce emissions from fire burning right now.

Images (c) velacreations

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