Pros and Cons of Rocket Mass Heaters

If you have made it to this site, you have obviously done some research on Rocket Mass Heaters. Not everyone will love a rocket mass heater in their home. They are very efficient, however, the efficiency comes at a price. They require a little more attention, due to their different style of operation. This page offers a Pros and Cons look at rocket mass heaters to help you decide if having one is right for you.

First, it is important to note that Rocket Mass Heaters are different than conventional wood stoves. It should also be noted that modifying the rocket mass heater to act more like a conventional wood stove will only defeat the purpose of having a rocket mass heater. If you want the stove to act more like a conventional stove, then you probably won’t be happy with a rocket mass heater. However, if you care about the environment and your fellow human beings, and are willing to do your part to clean up our air quality and help to keep forests populated, then it may seem like a good idea to own a rocket mass heater.

Below is a Pros and Cons list of a Zaug rocket mass heater as opposed to a conventional wood stove.

       Pros        Cons
The Zaug Stove (General)
  • Efficient
  • Produces large amounts of heat
  • Easy to use
  • Low pollution
  • Environmentally friendly
  • Beautiful
  • Saves money on wood purchases
  • Quality construction
  • Low maintenance
  • Can help you become less dependent on oil
  • Needs to be tended more frequently
  • Must be used with a thermal mass for efficiency
  • Thermal mass needs to be installed by a professional to be aesthetically pleasing
Fuel Source
  • Uses small pieces of wood or branches found commonly in your yard
  • Save money by buying less wood
  • Save time from splitting and chopping wood
  • Protects tree growth. Trees don’t need to be cut down for your warmth
  • Must tend the fire more frequently because smaller wood burns quickly
  • Need to cut wedges smaller
  • Need to gather branches
  • Can be ran horizontally to extract more heat from the exhaust
  • Run comfortably 25 feet before exiting the structure
  • Can heat a thermal mass, therefore, uses more of the heat from the stove
  • May form condensation in the exhaust line
  • Need to make the exhaust line air tight
  • Very easy
  • Can be done in minutes
  • Must install clean-outs along the exhaust line for access cleaning
  • Heats up fast
  • Very high temps for cooking
  • May provide too much heat in areas where it’s not wanted such as in summer
Steel Construction
  • 3/8″ Steel (very thick)
  • Beautiful design
  • Fabrication ensures that the stove will work the same every time
  • Two-tone paint can match any decor
  • Modern look
  • Eventually, the steel will wear out like any other wood stove
  • Repeated over firing can wear the steel out prematurely

Now here’s a look at our own two models in comparison head-to-head:

       Pro’s        Con’s

Standard Zaug Mass Heater
Standard Zaug Mass Heater shown in Metalic Warm Brown and Metallic Black


  • Burns hotter
  • Burns Cleaner
  • Weighs 100lbs less
  • Shipping cost is cheaper



  • Less of a burn time (30 – 45 mins)
  • Can’t see the fire
  • Small feed tube
  • Hotter fire means parts will wear out quicker
  • Feed tube gets too hot without RAPS
  • Must keep the lid open to operate

Zaug Altaire shown in Satin Black
Altaire by Zaug Stoves shown in Satin Black
  • Larger feed tube can be filled with more wood
  • Burns longer per full hopper
  • Beautiful industrial look
  • Glass door for viewing the fire
  • Can be ran with the door closed
  • Feed tube stays cooler
  • RAPS
  • Stainless ash drawer handle is attractive
  • Burns less clean (although cleaner than conventional)
  • Very heavy


So, there you have it. We have tried to be as forthright with our Pros and Cons as we could, listing all the complaints and all the advantages of a Zaug mass heater. You decide if this new heating style is right for you.

30 thoughts on “Pros and Cons of Rocket Mass Heaters

  1. Hi guys
    two points
    I had a cast iron stove that over the years I replaced all the parts that came into contact with the fire I ended up today with a stove that is as good as the day I bought it . So what parts are not replaceable on the Zaug . What failure would lead to it being a write off .
    Could you give more details about a suitable size “mass” to make efficient use of the heat .


    1. Hi David,
      The Zaug is still in it’s infancy and many ideas are being discussed and researched to make the Zaug even better. Among them are the solution you are seeking, with replaceable parts.
      The parts of the Zaug that come in contact with the fire are not easily replaceable at this time. We haven’t found an acceptable way to do that yet. However, we use 3/8″ steel for the inner burn chamber to counter the effect of wear from heat. It makes the stove heavy, but we feel it’s worth it in the long run.
      As for details on a suitable size mass- I would say it depends on the size room(s) being heated. Obviously, the more mass you have, the longer it will give off heat. The Zaug itself will warm a room fairly quick, but if you are looking for long sustained heat, the bigger the better.

      1. How about a lining of fire brick just around the fire box where the fire is hottest. Easily replaceable. Also in cases where the flue temp drops so much the draw is affected, how about a small fan to keep it moving just enough. After all wouldn’t the most efficient stove be one with the lowest exhaust temp, because all the heat was removed for heating use?

        1. Hi David,
          Our firebox is lined with 2 inches of perlite volcanic rock, held in place with a steel frame. It transfers heat even less than firebrick, and it weighs only 1/10th that of firebrick, for shipping. We’ve discussed other solutions as well, such as castable ceramic brick, however, the cost of materials alone is $200 for one stove. Not to mention the labor to set up the cast. So, we have to take all things in to consideration and what we feel is most important, is to maintain a reasonable price for the customer.
          As for the small fan, we stay away from designing anything after the exit port of the stove. A fan might be kind of neat though.
          You are correct, if all the heat was removed from the exhaust line, you would be using close to 100% of the heat produced in the stove.

          1. I bought a fan for this purpose from Canadian Tire but even on the lowest speed it gives too much air to sustain fire. Makes a real mess blowing ashes and fly ash all over. One needs to find a fan that you can dial down to just above a whisper. If you find such an item please advise me. Thanks Thomas

  2. I was just reading the comments wondered if a monolithic refractory would work. I believe an onsite molded product is available.

  3. What if you attached a woodstove in the front of the rocket chamber, in able to have enough wood to burn all night? to have to tend to it constantly (every hour or 2) would not bode well for a decent nights sleep. We just bought a Englander wood stove from home depot. it has a 2 stage burning area, with perforated rods in the inside top of the stove that burns the extra “gases” and looks like a propane burned that you see in a gas grill. I use a 3rd less wood per year. But the rocker burner idea looks more efficient. I would like to incorporate the combo to cut my wood consumption in half again. Also, I’m concerned about pipes clogging up with soot. Wouldn’t the pipes clog up in such a twist and turn sections?

    1. Hi Joe,
      The “decent nights sleep” comes after you heat up your thermal mass. This is a new way to use heat. With our stove, you will light it long enough to heat up your mass, and once the mass is heated up, the fire in the stove can go out. The thermal mass will give off heat for hours and hours without the Zaug even being lit. However, you don’t have to let it go out if you don’t want to.
      As for the wood stove chamber added to the front of the rocket stove- There is quite a bit of engineering involved with the way a rocket mass heater works. If you add a larger burn chamber to the system, the fire will not have sufficient airflow to heat the flame up to 1200 degrees (F) to burn clean and push the exhaust out properly. If you somehow added ports for airflow and could somehow generate a 1200 degree flame in that huge box, the amount of heat you would produce would melt down your steel, and probably burn your house down. It would be completely unsafe. Inside the Zaug, the burn chamber is only 6″ x 6″. In this amount of space, the flame can heat up to 1200 degrees, and the force of airflow is powerful enough to send the heat 25′ through a horizontal duct. Although, we did have to step up our steel to 3/8 inches in order for the steel to stand up to the high temps.
      As for soot buildup in the pipes- A rocket mass heater burns much cleaner than a conventional wood stove. It only smokes when it is heating up. Once the inside burn temperature reaches 1200 degrees (F) (usually in 20 minutes or less) there is no more smoke. The exhaust becomes clear. However, that doesn’t mean that soot doesn’t build up in the lines, it just means that it happens slower. Ideally you still should clean your exhaust duct once a year just like a conventional wood stove. It’s important to note that when installing a vertical exhaust run, clean outs need to be placed in such a way that the entire exhaust duct can be accessed for cleaning.

      1. Could you please add a drawing to your website how and where clean-out should be placed along exhaust run so that we can get an idea of how to build the exhaust run inside the thermal mass for easier clean out. Thank-you

        1. Generally, the clean outs should be placed in such a manner that the entire exhaust duct can be accessed and cleaned out with a flue brush and vacuum. We don’t discuss the exhaust line much because every exhaust line is going to be unique to the customer and their situation. Does that help?

          1. Hummm…. well then it really sounds like the whole heater must be moved once a year to have full access to clean out the entire exhaust vent to me .

          2. The top comes off of the stove for cleaning, and gives you access to the entire burn chamber within the stove. All you need to do is give it a quick vacuum with a shop vac to remove the ash. You don’t need to move the stove to clean it out. For the exhaust line, it’s as simple as pushing a flue broom through the line and running a shop vac in the line to remove debris. It’s very simple. It’s actually easier than cleaning a conventional wood burning stove because you don’t need to access the flue from the roof.

  4. Would a high temperature alloy add too much to the manufacturing cost to be used for the burn chamber? Something like Inconel which has a melting point range between 2425 degrees F and 2950 degrees F, or maybe something with tungsten or a tungsten alloy. I know tungsten is expensive but it does have an extremely high melting point of 6098 degrees F.

    I’m not sure if either of these would offer an affordable solution or if they are safe to use in this manner (possible toxic fumes and such) but I really like the idea of using a rocket heater as a responsible heating solution.

  5. Could you burn household trash? Sort of like having your own home incinerator? 🙂

    1. Sorry Doug,
      It’s intended for burning wood only.

  6. I don’t see a Washington State Ecology emmissions certificate – whats with no certificate?

  7. Curious, as the fire burns down most fires will produce smoke. How does a rocket stove handle that problem. The no chimney needed is intriguing.

  8. Howdy, Very nice – glad to see you continuing to refine the build options and quality – always a good sign for any product. Also appreciate the “green” nature of the rocket stove and your commitment to helping others be green. It make sense to me that laying out the venting is dependent on each person’s potential layout in their home. It wonder, however, if it would be useful to provide a link or two to some really nice systems folks have built as examples – with a disclaimer that they are exactly that and no more.

    in response to Doug’s note about emissions certificate – the answer is most likely the costs, grinding inefficiency, and bureaucracy of the EPA to make certification for something they are not accustomed to yet. Bureaucrats don’t do well with something new.

    Keep having fun making it better and better – great stuff.

  9. Glad I found you guys! Your work is your certificate! Can’t wait to order one. You need the EPA certification to sell, eh?
    Wish you luck. Your tree video was funny!

  10. I would love to see your product on the market. My fireplace is less than worthless.

    Hopefully the new EPA and EPA Secretary (Scott Pruitt) will help expedite needed products like yours to market.

  11. Do you have any UK sales office?

  12. I would really like to set one up in my greenhouse. When you resume production what price range are you thinking for the Zaug?

    1. It will probably be close to the old price range of $2100-$2500.

      1. Any sort of projection on when you’l resume production?

        1. In order to get to production, we need to raise $200K to get a new prototype built, drafted, tested, patented and certified. I don’t really have a plan for getting that amount of financial backing. Got any ideas for us?

          1. Approach Elon Musk for a loan

          2. That’s actually a good idea!

          3. Shark Tank LOL. GoFundMe. Can’t you build and sell a unit not certified for indoor use?

          4. Here in Washington State, it’s a $10,000 fine for selling an uncertified stove.

          5. I get what you’re saying but if a “wood burner” is sold for outside use would it not fall into the same category as a simple fire ring?

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