A better furnace? A look at woodburners, rocket mass heaters, and waste oil burners.

Recently I’ve been at the cabin. As the November chill sets in, I load up the wood-burner a couple times a day. I am left wondering, though, as I put in log after log, whether our old woodburner is as efficient as it could be. After all, it is basically just a cube of steel and a fan…is there a better way to heat the house, or a more efficient way? Maybe there was even a way to use a different fuel altogether? After changing oil on cars for several years up here, we’ve accumulated a lot of drain oil, maybe that could be used?

This was my question: is there a better way to heat a home than using a Jensen 24a (a very popular and time tested) wood-burner? It did not take long before I found a very novel way of maximizing the efficiency of a wood-burner. This solution is called a rocket-mass heater. The rocket mass-heater counters the problem of losing heat out of the chimney. The rocket-mass heater remedies this by directing the chimney horizontally through a mass of energy-absorbing material called “cob” (according to rocket-mass heater proponent Paul Wheaton, it is very similar to adobe).

Here is a rocket mass heater inside a cabin. As you can see, the cob heat absorbing material can double as a heated wrap-around couch.

The advantages to rocket-mass heaters include increased burning efficiency and less heat being released through the chimney. The cob material also has the advantage of retaining heat after the fire goes out. Waking up to a cold house in the morning is a common problem with wood-burning stoves that are not tended through the night.

How do they work? What makes a rocket mass stove a rocket mass stove? Well, three components differentiate it from a conventional stove. First, a “j-shaped” tube ensures greater combustion of wood, a steel barrel acts as a radiator for heat, and a masonry bench acts as a heat retainer as exhaust gases pass through it. The digram below gives a basic example of the heating method.


There is a lot of literature on the market that shows how to build the furnaces. There is less scientific literature, in fact the only article I could find is here. However, their popularity and growth is a testament to the effectiveness.

Well, it looks like rocket-mass heaters are a definite contender in the best home heating method. Their efficient, they burn clean, and they can be downright stylish. But there is another contender in the running: the waste oil burner!

The waste oil burner is basically the rocket-mass heaters evil twin. It is pretty filthy and seems dangerous even. It burns the drain oil from automobiles in a very “I don’t give a damn” manner. What good could it possibly be? Well, let’s give it a chance and investigate.

Well, if you’re like me, you have a lot of drain oil from cars laying around the property that you have been avoiding taking to the recyclers. It turns out this is not such a bad thing. Why? Well, you are sitting on a small fortune of black gold, that’s why! This liquid can be used to power an inexpensive furnace to heat garages, barns, pools, spas, and even homes.

Waste oil burners can be made cheaply from 55-gallon drums or 40 gal propane tanks. Though designs can vary, many use compressed air powered spray nozzles to atomize the liquid that can then be lit aflame. They seem to be popular in New Zealand where heating costs are high. As a matter of fact, pre-fabricated burning units can be bought from dripfedwasteoilheating.com, a New Zealand based website. Below is a good example of a waste oil burner on tape. Note the high temperature of 900 °F and awesome accent! This model also has very low smoke output out of the chimney.

This type of furnace offers a few advantages over the rocket-mass heaters. First, the fuel can be found free. I suppose the same can be said for firewood, but waste oil is almost always free on craigslist and is very common. The build time for a furnace like this would also be less in my estimation.

The obvious disadvantage to this type of furnace is safety. Oil has inherent dangers that firewood does not. Not only this, but oil also poses cleanliness challenges that make it less attractive as an in-home option. It can be done, but would require more care and precaution. After all, it is easier to clean a spilled bucket of firewood than a spilled bucket of oil!

This $24 Delevan nozzle is a popular choice in building a waste-oil burning furnace. This is just one necessary component to the furnace. Click the image to access this eBay item.

However, waste oil burners are an attractive option for garages, barns, hunting sheds, and so on. Maybe these two designs could be hybridized in some way. It seems like adding a masonry component to the waste-oil burner would make it safer (user is less likely to touch the extremely hot metal) as well as offer the advantage of heat holding capacity that the rocket-mass heater has.

It is hard to say which technology is better because they seem to differ in their best application. Both are low-cost, innovative designs that offer users inexpensive heat.



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