Heat Pumps and Home Efficiency

Home heating oil is the fossil fuel most consumed in Maine, besting gasoline by a short margin. Maine is the state most reliant on it for heat, with 3 out of 5 households using it. Heating oil is one of the most carbon intensive fuels used for heating, with propane and natural gas emitting less CO2, and coal emitting more. Heating oil is also expensive and its cost is volatile.

Wood is the most affordable heating option and is a popular primary or secondary heat source. Wood emits the most CO2, sometimes more than coal, depending on its moisture content. While wood is a renewable resource and may be technically "carbon neutral," it is not climate neutral. While new trees can grow and absorb some of the CO2 emitted by trees that are cut down and burned, this relies on good forestry management, and it takes a long time for CO2 to be recaptured. Because of this delay and the fact that CO2 captured in the future won't help with the effects of climate change now, data shows that increasing the use of wood for heat will actually increase global temperatures.

Heat pumps aren't a new technology, but they were designed mostly for cooling until the 2010s, when manufacturers started introducing models specifically for heating, and designed to work in cold climates like Maine's.

Heat pumps transfer heat rather than generating it, so they use up to 60% less energy overall than any other heating source. They are most efficient when temps are in the 40's or 50's, with 300-400% efficiency, with efficiency dropping to around 200% in the teens. They still produce heat even below zero, down to -13 for the best models, but the efficiency is closer to 100%.

Even at their worst efficiency, heat pumps are more efficient than any other source of heat. The next most efficient source is baseboard electric at 100%. Most efficient fossil fuel furnaces and boilers can reach the high 90's, but older furnaces can be as low as 56% efficient.

Efficiency is only part of the equation, and doesn't directly equal CO2 emissions or cost. Since Maine generates almost two thirds of its electricity from renewable sources, electric heat pumps emit a fraction of the carbon emissions of any fossil fuel or wood heat source, and will only emit less over time as the grid becomes greener. While Maine imports some electricity, 10-30%, utilities are required to provide at least 30% of their electricity from renewable sources, which will increase to 80% by 2030. Most of Maine has high electricity costs from investor-owned utilities, but even with the higher cost of electricity, heat pumps have a similar or lower cost than fossil fuels because of their high efficiency, and costs are less volatile. Costs can be lowered significantly by weatherizing homes so they need less heating, and using a secondary heat source in extremely cold weather can also help lower costs.

Heat pumps have other benefits, including built-in air conditioning and dehumidifying, and they produce no indoor or local air pollution. Heat pump technology is proven to be effective in our cold region, and data from Efficiency Maine shows wide adoption in Northern and rural Maine.

Over 100,000 heat pumps have been installed in Maine homes and businesses since 2019, surpassing the state’s goal two years early. The state now has a new target to install 175,000 more heat pumps across the state by 2027, which would bring the total installed to over 320,000.