I was recently at an event where somebody said to me that stoves weren’t rocket science and he knew he could build one himself because it was just a black box with some fire in it. Needless to say things got fairly heated (pardon the pun). Surprisingly as it happens, there are lots of crossovers between rocket science and quality stove manufacturing. The number one crossover is combustion, to create lift a rocket needs thrust which is created using the combustion of rocket fuel. We all remember the disastrous consequences of not having the shuttle insulated correctly when it came back into the earth’s atmosphere. To shorten the story we insulate the firebox of our stoves which in turn creates more combustion because of the increased temperature of the firebox. We then introduce super-heated air into the firebox which re-ignites the gas created from burning the fuel in the first place, thus creating more heat from gas that would have otherwise went up the chimney. This would be similar to an afterburner on a jet. Burning wood in a high efficiency stove is carbon neutral so it is only releasing the same amount of CO2 into the atmosphere that the tree took in over the course of its life. Responsible forestry companies will ensure that there is an infinite supply of wood by replanting forests. Each piece of wood that is burned has a calorific value which is dependent on its moisture content and whether it is a hard wood or a soft wood.
This is a simple graph to show the output in kW per KG of wood. If you are burning wood that is too wet you are wasting the potential heat output and will have to burn up to twice the amount of fuel to get the same heat output as dry wood. GJ/tonne = 19.2 – (0.2164*MC), where MC is the moisture content as a percentage of the total weight. A moisture meter is a great way to test the moisture in wood. A moisture meter uses two prongs inserted into the wood to test the conductivity. The wetter the log then the more conductivity there is in it.
So getting back to our space mission, all stoves nowadays have to go through rigorous testing using various scientific calculations for heat output, fuel input, water heating, efficiency, emissions and safety tests including CO2 levels. Here at Boru Stoves we have our own test laboratory where we carry out all of these tests before we send them for certification in Europe. To conclude, yes in a showroom a Boru Stove may look like a black box with some fire in it, and it may not have any resemblance to a rocket, but just remember that there is a lot more science involved.