Good news about climate solutions is always welcome, so it was encouraging to encounter Les Otten’s piece (“The efficiency of local heat,” Dec. 3) about his personal and professional favorite heat source: wood pellets.
Sadly, however, his airy dismissal of heat pumps in favor of pellet stoves skipped over a few facts that complicate the picture.
Mr. Otten’s brisk summary of heating appliance efficiency (“ratings in excess of 85%”) fails to note that while wood pellet stoves might achieve 85%, heat pumps are actually 400% efficient at moderate outdoor temperatures, and they produce zero waste heat.
It is true that as temperatures drop, so does the efficiency of a heat pump, but his claim that heat pump efficiency declines to that of resistance heat is not in fact true. Even at sub-zero outdoor temperatures the heat pump efficiency is 200%, twice that of resistance heat. The seasonal average is about 300%.
And then what does this mean: “While heat pumps are good for warming a home, wood pellets are simply better for heating”? Try this: While pellet stoves aren’t good for cooling, heat pumps cool better than a window air conditioner.
Otten claims that it is “an undeniable truth” that “wood indisputably has the best carbon footprint,” citing the “biogenic” nature of its carbon. Carbon in the atmosphere is carbon in the atmosphere regardless of its source.
The carbon neutrality of biomass burning is much in dispute due to the timescale of carbon dioxide uptake. The CO2 from a tree burned today will take 30-plus years to be taken up in regrowth. We don’t have those 30 years to address the problem. Furthermore, any biomass not burned is that much less CO2 produced.
Yes, the electric grid currently relies about 60% on fossil fuels, but this is rapidly shifting with the growth of renewables. With Maine’s current energy mix, for every 1,000 BTU of heat into the home, running a heat pump produces around 35 grams of CO2 , while burning wood pellets produces around 290g of CO2, more than eight times as much. If you are able to use 100% carbon-free renewables for electricity, the pellets would produce 80 times as much CO2 for the same amount of heat.
Does Mr. Otten believe pellet stoves could be the primary heating source for most Maine homes? How much wood waste is produced annually in Maine? The late University of Maine at Orono mechanical engineering professor and energy guru, Dick Hill, once calculated that it would take more than the area of Maine to sustainably heat Maine with wood. We invite calculations portraying an alternative conclusion.
Meanwhile, we believe wood and pellets make sense for backup heating in Maine homes.
Paul Stancioff is a University of Maine Farmington professor emeritus of Physics. Cynthia Stancioff is a retired English major seeking climate solutions and edible wild mushrooms. Their “Energy Matters” column has appeared in Sun Journal affiliates since 2020.
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