At first glance, the phrase ‘a rocket mass heater for a tiny house’ sounds contradictory, but actually, it is complementary. One of the reasons people live in tiny houses is that they wish to leave a lighter carbon footprint on the earth. Rocket mass heaters (RMH) can heat your tiny house, cook your food, and heat your water using only 1/10 of the fuel of a traditional wood stove.
Some sources say that it creates less than 2% of CO2 emissions of natural gas or electric heat. According to Alan Booker, executive director of the Institute of Integrated Regenerative Design, rocket mass heaters are not only a carbon-neutral form of heating, they can even be carbon-negative! Alan’s ideas are discussed in this thread on permies.com. Yes, burning wood to heat your tiny house can reduce the carbon going into the atmosphere!
What is a Rocket Mass Heater?
A rocket mass heater combines the thermal mass involved in a masonry heater with the efficient combustion of a rocket stove. It grew out of Ianto Evans’ work in Central America, where he created a cooking stove that was more efficient and safer to use. Later he adapted this with a thermal mass for home heating in Oregon. The design features that set it apart are:
- an insulated combustion chamber where fuel is burned with high efficiency at a high temperature
- a large thermal mass that absorbs most of the generated heat before the gases are released into the atmosphere and slowly radiate into the living space.
How Does a Rocket Mass Heater Work?
Traditional wood stoves often send most of their heat straight up the chimney. But not a rocket mass heater! The simple, yet ingenious design, ensures the complete combustion of wood, extracting every possible bit of energy before letting those gases escape through the chimney. The heat that would have been wasted up the chimney is first circulated in a bench that absorbs the heat, radiating it into the air or to bums sitting on it.
That means more heat in your home and less waste up the chimney. This short video, What is a Rocket Mass Heater, explains how it all works. Rocket mass heaters are a proven, though not yet as widely known as their far more costly and complicated cousin, the Masonry Heater.
Because of the unique design, the rocket mass heater reaches temperatures much higher than conventional wood stoves. The hotter fire burns off any creosote and other burn by-products. Creosote is a black suitable for Tiny Houses. It is made from 1-3 fifty-gallon metal drums stacked, a standard insulated J-tube that is surrounded by a mass.
The mass can be pea gravel, cob, broken bricks, etc. For a discussion of the design, check out the cottage rocket thread on permies.com. Check out the updated cottage rocket plans for details on how to build one yourself.
A prettier, but slightly bigger version of a rocket mass heater in a tiny space is the Cyclone rocket mass heater. The burn barrel is encased in brick and cob. This variation has more mass than the Minnie Mouse, but it is still very compact.
A pebble-style rocket mass heater is also suited to small spaces. This design has a pebble mass bench, an innovation by Paul Wheaton, the Duke of Permaculture and founder of Permies.com. Pebble-style heaters weigh less, allowing them to be moved and modified more easily.
This heater was designed specifically to heat a small space with a wooden floor, balancing gentle radiant heat and thermal storage with no hot spots. This creation takes up more space, but that space doubles as a seating area. The length of the bench can be designed to fit whatever space the homeowner has.-like substance, one of the many undesirable by-products of incomplete combustion and it is the leading cause of many chimney fires.
The complete combustion of a rocket mass heater fire means there is no creosote build-up. The RMH stove burns so cleanly that there is barely any smoke coming out of the chimney.
Rocket mass heaters are so efficient that you could heat your home with just twigs or deadfall from your property. Since you need less fuel, you will also save time by not having to chop, stack, and move all the chords of wood that you would normally! It is hard to believe, but it is true. Most are designed to take small pieces of wood, unlike the regular wood stove. It’s almost like having free heat!
Examples of Rocket Mass Heaters
But wait, you say, the point of a tiny house is to have less stuff. A rocket mass heater brings to mind something very large. At Wheaton Labs, the hub of rocket mass heater innovation, there are (almost) massless rocket mass heaters. One example is ‘Minnie Mouse’. Chris McClellan, aka Uncle Mud, is the natural building and rocket mass heater consultant who made this variation for small spaces that he calls the “Cottage Rocket.”
This cottage rocket has a cob hat on top of the burn barrel. The addition of the cob hat allows the heat radiating off the top of the barrel to be ‘stored’ and released later, making for a more stable indoor temperature while the rocket mass heater is firing. To see Minnie Mouse in action, check out this YouTube video: The Love Shack; a tiny house/cabin with a tiny rocket mass heater.
The Cottage Rocket was designed specifically to minimize size and weight and would probably be the most suitable for Tiny Houses. It is made from 1-3 fifty-gallon metal drums stacked, a standard insulated J-tube that is surrounded by a mass. The mass can be pea gravel, cob, broken bricks, etc. For a discussion of the design, check out the cottage rocket thread on permies.com. Check out the updated cottage rocket plans for details on how to build one yourself.
A prettier, but slightly bigger version of a rocket mass heater in a tiny space is the Cyclone rocket mass heater. The burn barrel is encased in brick and cob. This variation has more mass than the Minnie Mouse, but it is still very compact.
A pebble-style rocket mass heater is also suited to small spaces. This design has a pebble mass bench, an innovation by Paul Wheaton, the Duke of Permaculture and founder of Permies.com. Pebble-style heaters weigh less, allowing them to be moved and modified more easily.
This heater was designed specifically to heat a small space with a wooden floor, balancing gentle radiant heat and thermal storage with no hot spots. This creation takes up more space, but that space doubles as a seating area. The length of the bench can be designed to fit whatever space the homeowner has.
Can I Make One?
Rocket mass heaters are perfect for DIY. The materials are simple and easy to find: refractory clay brick, a burn barrel, pebbles, cob (sand, clay, and straw), and stove pipes. It has been estimated to cost $200-$600 dollars, depending on various factors like the size of the rocket mass heater and what materials you have on hand. In addition, most builds can be done easily on a weekend.
Other Uses for Rocket Mass Heaters
Still don’t want to fork over the interior real estate? There are endless possibilities for leveraging Rocket Mass Heaters for other homestead uses, indoors and out, from garden season extension to cooking, and heating water, to building a rocket ceramics kiln or forge.
In previous years, the Rocket Mass Heater Jamboree at Wheaton Labs in Montana has been at the forefront of innovation in rocket mass heater technology – if you’d like to see the event return, register your interest by posting a message here.
Among the most popular contraptions built during these events is the rocket oven which can heat up in 25 minutes with almost no smoke while using a tiny fraction of a wood most pizza oven. To learn more about Rocket Mass Heaters and other off-grid, low-tech solutions, consider coming to the renowned Permaculture Technology Jamboree in the summer of 2024.
Tickets are now on sale or work-trade positions are possible. No time? Illustrated step-by-step plans for the novice and more advanced DIYer along with more information about Rocket Mass Heaters can be found at the Free Heat website.
Summary
Rocket mass heaters are hyper-efficient wood-burning stoves that are an environmentally friendly way to meet all your heating needs and more! Indoors, outdoors, and in the workshop, there is a use for rocket mass heaters everywhere.
It is a little-known, but well-proven technology that anyone can build and customize to their unique situation. Finally and more importantly, we are convinced that it is a solution to climate change if it were to be adopted by the masses.
More Links:
- https://richsoil.com/rocket-stove-mass-heater.jsp
- https://permies.com
- https://richsoil.com/wood-heat.jsp
- https://freeheat.info/
- https://wood-oven.net/
Written By Monica Truong for Tiny House Magazine Issue 132
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