The Most Efficient & Inexpensive DIY Wood Burning Stove

Space heating system plays an important role in our life especially if we live in a cold place. Choosing the right heating system makes the difference in terms of sustainability, comfort, maintenance, environmental impact, etc.

There are many kind of fuels to choose from when you want to heat your space and one of the most sustainable is wood.

Wood is a renewable resource: it will regrow after some years.
You can find wood near your home especially if you live in a rural area or you can even cut it by yourself.
wood is not affected by market fluctuations as the fossils fuels.

But consider that a badly designed wood heating system could turn into your worst nightmare:

high fuel consumption
waste of time
production of high quantities of ash
high pollution
insufficient heating
frequent maintenance
safety problems

Note that this is not necessarily linked with money because you can spend a lot to buy the latest type of wood stove and face some of the problems above.

I want to share with you my experience about wood burning stoves because I want you to know that there is the possibility to build by yourself your perfect stove that satisfies all your needs without spending much money.

Background

Some years ago I was trying to find a way to heat my country house and I didn't have many alternatives to the wood since the place is pretty isolated so I started searching in internet for a good wood stove that could meet the requisites:

efficient
durable
powerful
cheap
low maintenance
safe
low polluting
possibility to cook
heat sanitary water

I browsed many last generation wood stove and thermo fireplaces but none of them satisfied all my requirements (maybe I was asking to much?). Firstly it was pretty difficult to find an efficient stove capable of both heating water and cooking, secondly they were hell expensive although made by simple materials and without a refined design.

The "do it yourself" option was my only possibility left but I didn't want at all to copy that metal box stoves capable of pushing out half the heat out of the chimney. I wanted to build my own stove and it had to be efficient, period.

I stumbled upon the rocket mass heater. This is a wood burning stove that you can build by yourself with inexpensive materials and it does work.

The rocket mass heater

It was a totally new concept for me: a stove that does heats not only the ambience but directly heats people! Because you can sit over the hot couch and feel all the warm this extraordinary stove can give you. This is only one of the many exciting features, another one is the radiator that provide instant heating since the first minutes of operation and let you cook over it.

The most efficient wood burning stove

Why should be this the most efficient wood burning stove?

it can extracts most of the heat from the exhaust gases while conventional stoves need the chimney to be hot to ensure enough draft to work properly.
the extremely high burning temperatures guarantees a clean and efficient combustion
the rocket mass heater features an internal insulated chimney that reaching extremely high temperatures creates a draft capable of pushing the exhaust gases through a long duct that extract their heat until they exit from the vent.
owners claim an 80 - 90 % reduction in wood consumption compared to a conventional metal wood stove.

Why should you build a rocket mass heater?

It's actually easy to build: you don't have to be an engineer, an hydraulic or an house builder.
You can build it using recycled or inexpensive materials without spending a dime.
You can build it within two days or less.
It requires little maintenance
Easy of tweaking or restyling according to your needs: being built by natural materials it's very easy to modify a rocket mass heater, you don't have to use a jackhammer or a welder.

Efficiency: because you don't want to waste heat, wood or time.
EcoFriendly: you can build this stove with natural materials avoiding the use of cement, glue or paint. You can even avoid the transport of materials because in most of the cases you can take what you need directly from the building place.
Multi purpose: heat yourself, the ambience, the water and cook.

How it does work?

There are two main ways of building a rocket mass heater: using the J-shaped design or the L-shape design.

In a rocket mass heater featuring a J-profile the wood is placed into a vertical feeding chamber and it should feed automatically the stove by gravity. The flame runs horizontally through the burning chamber until the 90 degree angle that causes strong turbulences ensuring proper mixing of oxygen and the smoke setting the stage for a second combustion.

The heat riser practically is a well-insulated chimney that causes a rise in the temperature. This creates a strong draft capable of pushing the exhaust gases through a long funnel, located beneath the bench, until the vent. After the hot gases exit the heat riser they are involved in a second combustion where all the flammable substances are burnt (complete combustion). they hit the surface of the radiator and give way a big part of their heat cooling down and descending to gather in the exhaust duct. The radiator instantly warm the room by irradiation and by generating convective motions with the air in contact with it.

The high efficiency of this stove is due to the proper insulation of the burning chamber and heat riser allowing the fuel to burn at the highest temperatures with a clean and complete combustion so that all the inflammable gases are burnt before they reach the exhaust duct.

While the smoke flows trough the exhaust duct it gives the residual heat to the thermal mass of the bench. The thermal mass is made of materials capable of storing a great quantity of heat and releasing it slowly acting as a thermal battery.

A thermal mass with an adequate size being totally heated is still capable of releasing heat the day after the stove has been switched off.

Finally what exits the exhaust vent is essentially low temperature water steam and CO2.

As you can see from the drawings the only difference between the two types of stoves is the feeding chamber: in a L-designed rocket mass heater it overlaps the burning chamber as you put the wood directly horizontally. You can read more on what's involved in my article J-shaped vs L-shaped.

Plans

My first rocket mass heater is based on the plans I bought from Ernie and Erica Wisner, experienced wood stove builders.

The plans featured a stove with a tall bench and 8" ducts which I built in just two days and since then I never stopped to tweak it and trying to improve it. I want to share with you my experience and all the improvements I made and spread this info as much as I can too help all people that are searching for a cheap way to heat their homes.

These are mainly the changes I made:

converted the J - shape design to a L design
added a water heating system
made the exhaust duct entirely by bricks
improved the insulation of the heat riser

You can follow all the necessary steps to build the final version of my stove in the article: How To Build An L-shaped Rocket Mass Heater

or if you want to purchase detailed plans from Ernie and Erica Wisner use this link: Cabin 8" RMHeater - compact 8" diameter rocket mass heater

Legal stuff

Unfortunately the rocket mass heater has still not been safety certified by the Underwriters Laboratories so build it at your own risk and in accordance with your local laws. Please also take in account the problems involved with an eventual home insurance. Read this post on the permies forum about how to insure an house with a rocket mass heater.

If you live in Portland, Oregon you should thanks Ernie and Erica Wisner because they managed to obtain a 1-week approval process, see all the building codes.

If you live elsewhere study your local jurisdiction and remember that the stove may be exempt from EPA regulations and considered as a site-built masonry heater instead of a wood stove because of its weight.

Last modified on 02/12/16

Written by Davide Buldrini