The Rocket Mass Heater

"Provide for the worst and hope for the best." - Antifragile by Christian Nassim Nicholas Taleb

What if the whole electrical grid shuts down and you only have a few acres to live on? For thousands of years, your ancestors survived little more than this.

Very few plan for the worst. I'm one of those few. Given a few acres, could you survive using a hatchet, a few rolls of pallet wrap, a Swiss Army Knife, and a flint to start a fire? I hope so.

Good news: Keeping warm efficiently may be a solved problem. Meaning you won't need to clear-cut a forest to keep yourself and your family warm. Why?

Because the rocket stove burns 70 to 90% less wood than other wood stoves, is theoretically safer than any wood stove in history, heats virtually any small house or shop, and can be built by almost anyone for almost nothing.

It's (probably) safer, cheaper, stealthier and can be built by almost anyone using a few tools in a very short time. So what's the catch?

Don't worry. There is one. But before we begin... what's a rocket mass heater?

A rocket mass heater is a mass and exhaust system built around a rocket stove. A thermal battery catches most of the energy produced by the stove.

The stove itself is probably the coolest way to roast marshmallows. Especially if you like your marshmallows utterly annihilated.

But the Rocket Mass Heater is another thing entirely. The stove itself is a quick, easy build. The heater is NOT.

First of all, the heater goes indoors. The rocket stove is typically used outdoors, the same way your charcoal grill is probably outside the house. Because the heater is an indoor thing, stuff instantly gets complicated.

The catch:

Generally speaking, insurers and inspectors don't like you setting fires in your house because for thousands of years, people would end up burning down their house, dying from asphyxiation, get injured by smoke inhalation, burns, cutting wood and a thousand other things that don't happen when you throw a light switch or turn the dial on a thermostat.

The rocket mass heater is new-ish. (There's been 20 years of development or so.) It's been called a "peasant stove." i.e. it's designed to be very cheap to build and operate. Cheaper than coal, if possible.

While the heater itself can probably be built by one or two people for $500 or $100 (or free, installed in one weekend with very few tools, that doesn't mean you're going to pop a load of gravel and concrete in your living room and make a Rocket Mass Heater THIS WEEKEND. No.

You absolutely need to do your research so that you don't choke on odorless CO2 and die, obviously. All exhaust leaks are 100% your fault, and you can't afford any of them.

Unlike traditional woodstoves, the chimney fire risk is almost zero because the high-temperature, highly insulated combustion chamber uses smoke and creosote as fuel, resulting in much cleaner, more complete combustion.

Essentially, you're creating a tiny blast furnace which can and will melt (or burn through metal. Which doesn't sound inherently safe, but it's a massive improvement on

It's also relatively kid-safe. The exhaust pipes remain relatively cool to the touch, getting up to 120 degrees Fahrenheit.

But dealing with regulations (and work-arounds) can complicate your life substantially.

In addition, if it doesn't work or stops working, you have to repair it yourself. You're not going to easily find any old expert.

It's labor-intensive to build and to learn about. You don't just buy one and install it with a few nuts and bolts.

Buying a wood stove vs. Installing a Rocket Mass Heater is like the difference between buying a car and buying a horse.

When it works, it works great, burns a fifth to a tenth of the fuel. (It's NOT ten times less work, however. The small burn chamber means splitting the firewood smaller than for a wood stove, which is more work.

But to heat the same space, you do burn much less wood per day. The people who own them love them. It's theoretically as safe as central air, although there's very little data to confirm it.

Some ideas "should" be safer, but their designs ended up killing off lots of the early adopters. [Burt Rutan designed a forward canard plane that should have been inherently safer, but for various reasons, people kept getting killed in the prototypes.]

If you don't mind chopping and carrying in five to ten times more wood, then there's no reason to install a Rocket Mass Heater. So most people don't.

The people who want convenience are willing to pay for it. Very few people are so frugal that they'll invest the time it takes to install an experimental furnace in their home.

If, for some reason, you need to save on heating (and cooling) or needed to be energy independent on a smaller footprint, or you need to install a very stealthy wood stove, installing a rocket mass heater is one of the first upgrades I'd consider to your remote or off-grid shelter.

Even if it requires one of those pesky building permits.

Here, a man who understands thermodynamics improves upon the filthy hippies' thermal mass heater: