Better Wood Heat: DIY Rocket Mass Heater Movies

A rocket mass heater is:

  • cheap to run. About a tenth the cost of natural gas, electric or conventional wood heat.
  • clean. They emit about a hundredth of the smoke of a conventional wood stove.
  • good for the environment. Less than 2% of CO2 emissions of natural gas or electric heat. Can reduce your carbon footprint as much as parking 7 cars.
  • sustainable. It uses a renewable fuel which is easy to find and store.
  • cheap to build. About $200 to $600.
  • quick to build. Often built in a weekend
  • luxuriant. Like the luxury of a heated floor but without all that standing.

the front cover of Better Wood Heat 4-Movie set box:

wood heat videos

the back cover of Better Wood Heat 4-Movie set box:

back of wood heat videos

Movie 1: Cob Style

basic rocket mass heater

If a person was going to get just one movie, this would be the one. A cob style rocket mass heater is "the old reliable". We have two projects to demonstrate this wood heating technique. One in a log home and one in a tipi. We put one in a tipi as part of an experiment to test how warm a person can be with a rocket mass heater and zero insulation. We interview the couple that stayed in the tipi for the first winter, with a strong focus on how comfortable they were when it was 26 degrees below zero.

This will also be available as a standalone movie. We tried to make this movie dual purpose. Something that could fit within the new 4-movie set, and something that could fit for people that want just one movie.

Movie 2: Pebble Style

pebble style rocket mass heater

We will show the construction of three pebble style rocket mass heaters. The difference with these is that the mass is usually a wood bench filled with pebbles and rocks. A different wood heating aesthetic. These designs are (relative to cob style) easy to move and modify. They also tend to be lighter, thus, better for installing in places that have a wood floor.

Movie 3: Shippable Core

shippable core

The kickstarter from two years ago showed an early prototype. We were certain that by the time the video came out, people could buy a shippable core and plug it in. In the time that has passed, that didn't happen. We ended up releasing a variety of information on how to make your own - and now, in this video, we supply the "how to" video for a variety of techniques.

Movie 4: Innovators Event

rocket mass heater innovators event

Last fall we put on an event where Ernie and Erica invited several rocket mass heater innovators that they thought were the best in the world. Each innovator was provided with the materials to create whatever wood heating contraption they wanted. The results were: "the ring of fire" - a rocket mass heater shaped in a circle with glass to show the burn; an outdoor rocket mass heater/cooker/smoker; A "batch box style" rocket mass heater with measured output cleaner than anything we have ever encountered; An indoor rocket stove, griddle and water heater.

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Is a rocket mass heater cleaner than natural gas heat?

Yes. For rocket mass heaters where pollutants in the exhaust were measured, we have seen the exhaust cleaner than natural gas exhaust. In one test, 3/4 of a rocket mass heater burn had zero CO. In general, for heating a home over a year, the CO2 output for a rocket mass heater is less than 1% than that of natural gas.

Here are the test results of one rocket mass heater burn.

carbon monoxide graph

You can read more about the testing of this rocket mass heater in this discussion.

How is a rocket mass heater different from a regular wood stove?

A regular wood stove will extract heat immediately. A rocket mass heater will direct the fire through an insulated space to make the fire burn much hotter before harvesting the heat. This burns the smoke and creosote. Then most of the heat is extracted and put into the room. Any remaining heat is pushed through a mass to be slowly released over the next couple of days.

The smoke coming from a the chimney of a regular wood stove is typically 300 to 600 degrees and a large volume - and typically stinks up the neighborhood. The exhaust from a rocket mass heater is typically 70 to 120 degrees and a small volume - and is usually clear and without odor.

Here is a short video with Ernie Wisner in 2011 talking about some of his experimentation in trying to modify a conventional wood stove to be more like a rocket mass heater. This helps to convey how there are differences between the two

Regular wood stoves are 75% efficient now. I think the most you can improve is maybe 10%. How can you make the claim of heating with one tenth the wood? Wouldn't that be like claiming to function at 750% efficiency?

First, "75% efficient" isn't really 75% efficient. 16% is allowed for heat going up the chimney, so it is actually 59% efficient. And that was from the best burn in a lab under optimal conditions. An excellent operator might be able to get about 35% efficiency. Most people run their "75% efficient wood stove" at 3% to 15% efficiency.

We get the "one tenth" number from people that have replaced conventional wood stoves with a rocket mass heater reporting that they now heat their homes with one tenth the wood.

This rocket mass heater article has a lot of information explaining this.

This discussion was started by a skeptic and every ounce of skepticism is addressed.

This video is from 2010 and is a comparison for a home where a conventional wood stove was replaced with a rocket mass heater and now uses about one eighth of the wood:

This video is from 2012 and features a home in the Okanogan Highlands where they will have snow all winter. It shows how little wood is used:

The engineering behind the technology credits:

  • the inability to close dampers - the design is for a very hot burn every time, with a high volume of air splashing on the fire.
  • the mass extracting the last little bits of heat from the exhaust
  • the use of the mass reduces hot/cold fluctuations in the house which leads to a greater thermal differential between the inside and the outside
  • more use of radiant and conductive heat which is more efficient than the convective heat favored by other forms of home heat
  • the mass will absorb excess heat in the house when you have a lot of guests or do a lot of cooking
  • since heat is given off for days after the fire is out, three is less need for air exchange
  • the smoke and creosote are also used as a fuel


They are currently legal in all states for outdoor use. For indoor use it varries. Portland, Oregon building codes now allow rocket mass heaters indoors and many other places are adding them to their codes. In my area, they are legal in the northern half of missoula county.

Due to the benefits far above and beyond electric heat, natural gas heat and conventional wood heat, many people are building now, and are confident that their local codes will catch up soon and have elected to blaze a trail in their community.

Here is a discussion thread about when you need permitting, when you don't, etc.

Can you cook with a rocket mass heater?

Yes, but only when actively burning. Homes with a conventional wood stove might burn wood all day, or several times a day. People with a rocket mass heater tend to burn for less than an hour a day in winter. Sometimes every other day. Which does not lend itself well to cooking.

Many people will put a kettle on the barel.

There are some variations that do better for cooking. Movie 4 shows a design that does very well for outdoor cooking and another design that could be used for indoor cooking. We are seeing a lot of new designs lately for indoor cooking. Here is one from our 2015 innovators event that is primarily for indoor cooking, but can also warm a small bench:

rocket cookstove

Here are images from what is created in movie 4. The 3-in-1 griddle, oven and water heater by Tim Barker and an outdoor cooker/smoker/bench by Matt Walker:

rocket oven

rocket smoker

After the event, Matt Walker went on to create a really nice rocket cook stove:

How much does it cost to run?

We've heard from a lot of people that they heat their home with the sticks that naturally fall off the trees in their yard, so, for them it costs nothing.

We have one story of a guy that heated his home all year with junk mail.

If you choose to buy wood and have it delivered, the cost is usually about $200 per cord (about a mounded pickup load). We have a lot of people that are heating their home with about a half cord of wood per year. But depending on how cold it is where you are, how insulated your home is, how big your home is ... maybe you will need as much as two cords per year.

Are there alternatives to the barrel?

Yes. Thousands of people have fabricated (or had somebody fabricate) something that is shaped like a barrel, but it just looks like a plain cylinder. Some people have opted for stainless steel barrels and others have found ways to decorate a barrel.

Here is a picture of me sitting on one of the rocket mass heaters built in movie 2. Note that we used a stainless steel barrel here. And that the mass of the heater is a wood box filled with pea gravel and topped with granite slabs.

stainless steel barrel

Here is a fabricated cylinder (barrel) with some engraving:

rocket mass heater

Erica experimented with distressed copper:

copper barrel

Here is a basic, fabricated barrel of a wood heater in a yurt:

rocket mass heater

Peter van den Berg with his fat rabbit experiment at the 2015 innovators event - note that the "barrel" is just a fabricated cylinder:

fat rabbit rocket mass heater

Here, the barrel is replaced with a special quartz bell during the 2015 innovators event so we can see the torus that is formed when the exhaust passes from the riser to the barrel:

quartz barrel rocket mass heater quartz barrel rocket mass heater

What is "cob"?

A mix of sand, clay and sometimes straw. Kinda like adobe. It ends up hard, like rock, but is somehow easier to sit on than rock or cement. So far, cob has been the most popular material for creating a rocket mass heater.

Movie 1 is all about building a rocket mass heater with cob. In the movie 1 we build two cob style rocket mass heaters. The first is a very basic build in a log structure. The second is in a tipi to demonstrate the heating properties of a really well built cob style rocket mass heater:

cob rocket mass heater tipi rocket mass heater

This creator attended the workshop from the "Wood Burning Stoves 2.0" 4-movie set and he built this:

cob rocket mass heater

the candy at the end of the maze

How many of these have been built?

We think there have been about 200,000 to 300,000 built so far. Interest is huge and growing fast. I think we will hit a million soon.

Ernie Wisner, featured in all of these movies, has built over 700 rocket mass heaters.

Wood stoves are smoky. Saying that these have less smoke doesn't say a lot. How much smoke is there, really?

Here is a video from an earth day demonstration in 2010. You can see the fire burning and you can see clean exhaust. You can also see demonstrations of how cool the exhaust is.

How much does it cost to build one?

Indoor rocket mass heaters will cost more because you will want them to look nicer and be less likely to leak. Expect to spend $400 to $800 in materials for a nice indoor rocket mass heater. People have build rocket mass heaters in their shops for less than $20 - using a lot of scavanged materials.

Can it cause carbon monoxide poisoning?

Most concern for carbon monoxide poisoning comes from people confusing a rocket mass heater with a rocket stove. Rocket mass heaters were invented by Ianto Evans, and he based the designs on his work with rocket stoves. But a rocket mass heater has its exhaust vented to the outdoors. Modern rocket stoves tend to be more for outdoor cooking.

A well built rocket mass heater is safer than a natutral gas heater, a gas stove, a gas oven, a gas water heater or anything in your home that is connected to natural gas. In fact, if your wood pile has a "leak" you are much safer than if your natural gas system has a leak.

Will it work with a wooden floor?

Movie 2 shows a rocket mass heater installed in a manufactured home with a wood floor. Extra support is put under the floor.

Can I hire someone to build it for me?

We have heard of a lot of people buying the movies and giving them to their favorite builder for this very purpose.

Is there a book?

There are two excellent books.

rocket mass heater builders guide

This comprehensive book about rocket mass heaters just came out! This should put an end to the freak shows of flaming death showing up on YouTube mislabeled as rocket mass heaters - and put an end to getting the same questions asked over and over again. We can start every answer with, "Have you read The Rocket Mass Heater Builder's Guide?"

This book is written by Erica Wisner and Ernie Wisner. The stars of all eight movies. Naturally, a lot of the information covered in this book matches very well to the content in the movie. In fact, the primary example in the book is the cob style rocket mass heater built in the log structure in movie 1.

Oodles of details about the rocket mass heater builder's guide.

Erica and Ernie contributed heavily to this book which is now about ten years old. They even contributed to the third edition which came out a few years ago. This book is written by Ianto Evans, the inventor of the rocket mass heater and illustrated by Leslie Jackson. It is a delicious exploration of how a rocket mass heater works. While thousands of people have built rocket mass heaters using nothing but this book, things have come a long ways in the last ten years. This book is comfortable, enjoyable and of great value, but not so much a "how to" as much of helping you to understand "how come". More ...

wood burning stove plan

For many years before Erica started to write the builder's guide, she was cranking out detailed plans for rocket mass heaters that she and ernie had designed and built during a workshop. She would never relase plans until the installation was at least a year old and had proved to be a success. As the years passed, she amassed a LOT of plans, wrote several ebooks and even started share the earliest dabblings of her new book. Demand was high. Eventually she offered it all as one big gob of files.

Are there reviews?

This product is hot off the press, so most of the reviews are from people that supported our kickstarter. Reviews and discussion. So far the reviews all seem to rate these moviess as a 10 out of 10.

Is it on amazon?

I have put other stuff on amazon in the past. It turned into a lot of work and amazon takes a fat cut. Maybe someday somebody that is good at amazon-ing will buy a few cases from me.