Heat pumps are often promoted as the cornerstone of Vermont’s clean heating future. But a closer look at real-world data from New England reveals a more complicated truth—especially during the coldest months when heating needs are highest.
While heat pumps can reduce carbon emissions when powered by clean electricity, their performance drops significantly in cold weather. As temperatures fall, efficiency declines and electricity demand rises sharply. Field studies show that most homeowners stop using their heat pumps below 30°F—exactly when they’re needed most. On average, these systems are used for less than half the winter heating season.
This underutilization raises serious questions about the cost-effectiveness of current incentive programs, especially if the systems are primarily used for summer cooling. If Vermont is to meet its carbon goals, policy must reflect how these systems are actually used—not just how they perform in ideal conditions.
A successful thermal reduction strategy must be technology-neutral, grounded in real-world performance, and tailored to Vermont’s rural, cold-climate realities. Heat pumps have a role to play—but not at the expense of reliability, affordability, or environmental integrity.
Below is a relevant section of a Technical Review conducted by Raymond Albrecht, PE, in October 10, 2024 for the Vermont Public Utility Commission Clean Heat Technical Advisory Group. Learn more about Ray and read the entire paper here.
HEAT PUMP UNDERUTILIZATION BY HOMEOWNERS DURING COLD WEATHER
The graph below shows average electrical demand vs. outdoor temperature within the heat pump populations of the three largest field studies reviewed for this document. The graph shows a representative electric demand for a full-sized heat pump with capacity of 40,000 Btu/hr at 0 deg F, also for a partial-sized heat pump with a capacity of 15,000 Btu/hr at 0 deg F. The data curves for the three field studies show that actual electricity consumption was only a small fraction of what would be expected with full heat pump utilization. Note that the actual electrical demand curves are relatively flat below 30 deg F. This indicates very low heat pump utilization below 30°F. Since heat pump power demand increases dramatically as the outdoor temperature drops further, due to increasing heat load plus decreasing heat pump COP, this means further that the homeowner percentage drop-out rate is increasing as the temperature drops.
The bar graph below illustrates, in a different format, the same message re: low homeowner utilization of heat pumps during the winter. Homeowners have on average, been using their heat pumps for less than half of the potential winter hours of operation. Some homeowners indeed used their heat pumps dutifully even during the coldest days of winter, but most dropped out at some point as the weather got colder, or never even turned on the systems at all for heating purposes.
This raises the thorny issue of homeowners taking advantage of heat pump incentive programs to purchase systems that are used substantially for cooling and only partially for heating, whether upfront incentives vs. pay-for-performance should be provided to homeowners, and whether ratepayer vs. utility shareholder funds should be used for heat pump incentive programs. There is direct relevance of the heat pump utilization question to policymaking for the Clean Heat Standard in Vermont.
