Friday, September 9, 2011

Rocket Mass Heater

A Rocket Mass Heater

I have been intrigued by Rocket Mass Heaters ever since I heard of them about a year ago.  So what exactly is a Rocket Mass Heater?  Well, it is a variation of a Rocket Stove (don't worry if you haven't heard of that either) combined with the concept of a Masonry Stove.

The concept is simple and brilliant.  Wood is burned in a uniquely shaped "combustion chamber" that burns wood very efficiently.  The heat produced from the burning wood heats up a large thermal mass (usually some form of bench).  By the time the exhaust exits the room, it is only about 90 degrees F (32 C).  The exhaust is mostly water and carbon dioxide. 

Let me show you an illustration of a Rocket Mass Heater for better understanding:
Illustration of a Rocket Mass Heater

What are the benefits of a Rocket Mass Heater?
  • Use a lot less wood for heating.  The amount depends on where you live, but you can expect about one fourth to one sixth of what a very efficient fireplace or woodburning stove uses to heat a room/home.
  • Almost no pollution.  The fire burns so hot and intense, that only water vapor and carbon dioxide is released.  And for you "Carbon Footprint" Nazi's out there, it is "carbon neutral".  Clippings from branches in the yard or from branches fallen out of trees or even from coppiced trees is all that is needed in most cases.  All that is left in the combustion chamber is a little bit of white ash.
  • Better at keeping and sustaining heat.  Almost 90% of the heat produced stays within the home instead of being lost out the chimney.  The thermal mass can keep radiating heat for 12-48 hrs after the fire is out. 
  • Needs less tending.  As the heat is radiating long after the fire is out, there is no need to tend the fire or watch for spitting embers.
What are the downsides to a Rocket Mass Heater?
  • You need to build it yourself.  There is no commercial version available now.
  • It is heavy!  The thermal mass being made mostly of clay/adobe is weighs a lot.  You can't just install these anywhere.
  • It uses clay/adobe.  For some, this is great.  For others, well, let's just say a Rocket Mass Heater doesn't blend will with a New World Colonial Design.  (I actually have no idea if that is a design style or not, but it sounds pretty good!)
  • They take a while to warm up.  A big thermal mass can take up to 4 hours to heat up (but then it will retain heat for a long longer as well).
  • Building codes don't really know what to make of this yet.  It is a relatively new concept (2004 as I can best tell from researching it).
  • You can get some "smoke back" when initially lighting the wood or if the Rocket Mass Heater is not designed well.

WARNING: Sloppy hippy alert.  As is often the case, it is the more eccentric individuals who are the first to attempt/try new innovative projects like a Rocket Mass Heater.  These individuals are usually hippies.  These hippies are usually very messy or sloppy individuals who leave piles of junk all over the place.  Unfortunately, it is hard for many people to see past this chaos and find the gem underneath.  In my opinion, a Rocket Mass Heater has an amazing potential for energy savings.  I think they need to be made a lot more attractive before they will be adopted on a more widespread scale, but what an amazing concept!

Here is a pretty good video that highlights a number of Rocket Mass Heaters (with the aforementioned sloppy hippies).  It was done by Paul Wheaton of

This is just an introduction to the concept of Rocket Mass Heaters.  I plan on providing more detailed information in the future. Stay tuned!


  1. it's beginning to get a bit weird how we keep finding these things at the same time. I read an article on pocket rockets about 6 months ago. I'm nervous about them though - seems like they might explode - or maybe it's just the name that's making me worry.

  2. Ha! I think explosions are pretty rare (if ever). The main issue is smoke back. I think that is the main thing I am concerned about... that and convincing my wife to let me build a huge structure like this in our living room! Actually, I may try to have it incorporated into the home design... we'll see.

  3. All I will say is build the heater somewhere outside first and prove that it works. Watch the video again and pay close attention to the part where it says 4 inch duct work is not enough. You do not want your heater to operate like that. You want to know it works before you build it into a house.
    I don't think this thing could explode. The rocket thing is about how the fire burns. build a burn box and heat riser and then start a fire. You will then understand how it got the name Rocket. The fire burns like a blow torch. Otherwise the problem is not enough pressure. This is what causes the smoke back. I built one of these in my back yard and there area a couple of things that have to be right or they do not work right all the time.

  4. Great point. For any projects that have a potential to be dangerous (like pretty much anything dealing with fire), I recommend either doing as you say and building a "safe" version first or building with someone who has experience already.

  5. One of the books on my to read list is Rocket Mass Heaters Super efficient Wood stoves You Can Build (and snuggle up to) By Ianto Evans and Leslie Jackson (cob cottage publications) They marry function and style ;)

  6. I like the concept a cross between a wood burner and a storage radiator with a low carbon footprint , but would not wish to sit on a hot surface. I guess also folks in UK might not wish to have an oil drum in their living room, and if they get as to the high temperatures talked of, they won't last long.
    For personal safety I would at least wish for some sort of HETAS certification. For a different view take a look at

  7. We are using a 1/4 steel large steam vessel we obtained for free; all but the top three inches will be encased in mortar/cob, so that one does not have to have an oil drum in the living room, ours will also have a copper coil around it to heat water in a grid down situation.

  8. Isn't a Rocket Mass Heater just the same as a German "Kachelofen"...? They are there for centuries...

  9. Anon - Yes! The Kachelofen is an old technolgy that is very similar to the more modern Rocket Mass Heater. The Chinese had another similar technology centuries ago as well. These are all variations on a theme!


  10. This is a really good post. Must admit that you are amongst the best bloggers I have read. Thanks for posting this informative article

  11. Great info! I recently came across your blog and have been reading along. I thought I would leave my first comment. I don’t know what to say except that I have.
    custom heaters

  12. Love your site. Can't get off my chair as each new page keeps me here hour after hour.

    You mention: "You need to build it yourself. There is no commercial version available now."

    You may not know about tempcast. It is not a rocket stove per say but it does the same thing, that is burn little wood and keep a house warm for up to 48 hours between burns. I've never actually seen one but here is the site if you are interested in reading about them:

    More technical details can be found here: