The recent polar vortex has hit us all with some really harsh conditions and as a green contractor based in New York it has made work on our ecological construction sites difficult. Spending cold, winter days inside of an upcycled shipping container can leave you freezing for hours. Space heaters require electricity that you may not have access to.
We’ve figured out a way to heat our workspaces in an environmentally friendly and sustainable way that uses zero electricity and burns zero fossil fuels. A rocket mass heater is an efficient wood burning stove and space-heating system. Two key things differentiate them as ecologically sound space heaters.
The first is that the design involved creates a small, efficient, high temperature combustion chamber capable of burning significantly more carbon than simply burning wood in a metal can or bonfire. Due to the high carbon-burning capabilities less ash is created and the smoke emitted is much cleaner.
The second is that the cob or clay acts as a thermal mass that physically stores the heat created during combustion for hours and releases it into the space through convection thereby decreasing the amount of electrical energy or fossil fuels used.
A traditional rocket mass heater involves a 55 Gallon drum built into a clay wall and extending into a room so as to transfer the most heat possible. This form is too large and too permanent for use on multiple construction sites. The technical design of a larger scale heater is more complex, but we needed a relatively small heater that can be transported between sites.
The method of building a rocket mass heater outlined below enables environmentally conscious contractors and individuals to use materials that are more readily available or perhaps lying around the house or job site.
Here we’ve provided the simple DIY steps to creating a rocket stove or rocket mass heater:
Materials:
5-gallon plastic bucket
2 2-liter plastic soda bottles
Dirt, grass (or hay), and water
Marker
Duct tape
Utility knife
A piece of metal lath or mesh
Step 1: Use the marker to trace a circle 3-4 inches from the bottom of the 5-gallon bucket and cut out the circle with your knife.
Step 2: Use the duct tape to tape the ends of the soda bottles together in an L shape. The soda bottles should be filled with liquid or remain unopened.
Step 3: Use the dirt, grass (or hay), and water to make the cob in a different bucket.
Step 4: Put some of the cob in the bottom of the bucket to the height of the bottom of the hole you’ve cut. Place the bottles you’ve taped together inside the bucket with the end of one bottle sticking out of the hole that you’ve previously cut.
Step 5: Continue to fill the bucket with the cob mixture and be sure to smooth all edges. The clay will need a few days to dry out.
Step 6: When the cob feels dry pour the liquid out of the soda bottles and cut off the tops of the bottles. Remove the bottles and tape by reaching into the bottles and pulling them out.
Step 7: If your cob mixture is not fully dry let it set for a few more days. Then place paper and small twigs inside and light a small fire to dry the cob entirely.
Step 8: Place the piece of metal lath or mesh, small enough to fit inside of the hole, in the side of the bucket. This will hold the fuel being used to heat your space. It should be long enough that it sticks out of the bucket to hold longer sticks/kindling.
Step 9: Add your fuel (paper, sticks, any natural carbon-based material will do) and ignite!
This rocket mass heater is safe, environmentally friendly, and portable. For use indoors this structure would need to be ducted to allow exhaust or fumes to be safely expelled outside. Additionally, use of this type of heater in a home remodel is not recommended however for work on an industrial space it is a perfect fit.
Click HERE for a link to a smaller, even more portable version. We don’t recommend this exact method due to the high levels of BPA inside of soup cans so we suggest purchasing heater duct pipe (un-galvanized) to use instead.
Click HERE to see different designs for large scale and conventional rocket mass heater. These designs are meant to heat a home and emit smoke and any potentially dangerous fumes outdoors through a duct system.