Combustible Rejectementa

That is so 1980′s

3 decades ago I entered the green revolution when my parents purchased a pellet stove, which replaced their coal stove, which replaced their wood stove,…     Back then the quality of the pellets, the crudeness of the technology, and other factors made them a real pain in the keester.    Heaven forbid if the fire went out while you were sleeping, cleaning was an annoying daily ritual.   Since then I’ve mostly lived in the big city, where natural gas was cheap, efficient, and increasingly costly.

Back to the future…

So on moving out into the ‘burbs, into a stereotypical late ’70s house, we had to deal with the money sponge that is electric baseboard heating.   We considered a rather costly HVAC upgrade, which would certainly have reduced costs, but the ROI would have been approximately 10 years.   But with the $1500 rebate on biomass burning heaters, we spend a third the money, and expect a 5 year ROI.

Compared to my initial experiences with pellet stoves, the modern version is like some alien technology that fell to Earth.   And it looks good! Automatic everything, setback thermostat, multiple fuel capabilities, high total efficiency ( 83 – 87% ) which is outstanding for a wood burning appliance, and low particulate emissions compared to a traditional wood stove.   Engineered fuels are much more consistent, more available, and have undergone inflation at half the rate of fossil fuels.

Cool!   Goodbye coal fired electric generation, hello carbon neutral … blah, blah, blah    Who gives a crap about the planet, look at the impact on my electric bill!  Now I can afford to feed my kids.

Life is a bowl of cherries, I’m burning the pits

So, you like pie?   I like pie.  Even Forrest Gump liked pie. So where in the world do all the pits go?   They are dried and sold as fuel!   A single tree can produce 8000 pits each year.   A large scale orchard can produce enormous numbers of pits.   On a weight basis cherry pits produce about 20% more heat, but have half the density of wood pellets.   The net result is that they produce about 40% less heat at the same feed rate.   ( Feed rates in most stoves are proportional to volume, not weight, and so this is what matters when making the comparison.  Its one of the breakthrough improvements in this technology that has yet to happen. )

More is Less

So you are actually producing 40% less heat at the same feed rate.   You have much more combustion air being delivered to the firepot than is needed.  The pits themselves consist of a clamshell of incredibly hard, lignin rich material, and a small kernel – a cherry seed.   When they burn, they split into these pieces, forming small flakes of charcoal which are easily blown out of the firepot, or ejected as more are dropped into the firepot.   So they are a fuel which is more designed for bottom feeding  rather than top feeding ( as is the QuadraFire unit we have ).   The ash is paper white, fluffy, and very mobile.   With the pits being much less dense, you have to fill the hopper almost twice as often.   All these things conspire to make cherry pits more difficulty to burn.

Bargaining

One way to mitigate these challenges is to adjust the flame height as high as possible while achieving a clean burn.   This has the effect of feeding more fuel, but does not appreciably increase the combustion air flow.   This compensates, somewhat, for the lower density fuel, and reduces the volume of ejected ash.   And at low burn rates, this worked well.   But ultimately the low density of the pits means they do not perform as well in the more efficient stove where high air flow is a design principle.  Ideally, having the stove “know” about burning characteristics of the pits would be much better.

Warts and all, the pits actually might serve the purpose of a warmer weather fuel, where higher heat output is not necessarily required or desired.   It allows the stove to run more continuously on a day where wood pellets would produce too much heat – causing the stove to cycle on and off.   And of course the pits are, unlike wood pellets, an innocuous and inevitable by product of people eating pies.   So “no trees were killed … “  Whereas wood pellets are waste from harvesting a tree for some noble purpose.   Its the same difference between being a vegetarian and being vegan.

Acceptance

I guess with the right stove, and a cheap supply of pits, or some over arching moral imperative this would be a great option.   But I am quite happy to be down to my last bag.

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