Who's Afraid of a Polar Vortex?

A Case Study on Twelve New York State Homes

As more New York State homeowners and contractors switch to heat pumps, more information is becoming available about their cold weather performance. The winter of 2025–2026 brought three intense cold snaps to New York State with extremely low temperatures. During that period, the cold-climate air source heat pumps at twelve single-family homes from across the State were studied. Each home used its heat pump as the primary heating system during the cold snaps, and indoor temperatures held at or near the thermostat setpoints at every home.

Study Summary

• 12 single-family homes across 10 regions of the State
• All three Department of Energy climate zones in New York State represented
• No fossil fuel backup heating was used during the study
• Whole-home systems sized to 100%–150% of the Manual J^[1] calculated heating load
• 2025–2026 winter heating season, including three polar vortex weather events

Comfortable Indoor Temperatures During Extreme Cold

Contractors size heating systems, heat pumps included, to meet a “design temperature.” The design temperature is essentially the coldest outdoor temperature a home is likely to experience in a given winter, and a properly sized system should be able to maintain a comfortable temperature inside the house even in those conditions. During the study period, temperatures dipped below each system’s design temperature three times. Across the 12 sites, the lowest outdoor air temperatures recorded were between -19.5°F and 7.7°F, which was anywhere from 0.3°F to 13.2°F below the coldest temperature each system was designed to meet.

Despite the extreme cold outside, indoor temperatures stayed comfortable. The study recorded no unintentional temperature drops due to the outdoor conditions alone. The significant indoor temperature swings observed in the study were the result of a participant’s thermostat setting or an unrelated equipment issue. For example, some participants set their thermostat to a lower overnight temperature, one participant left the thermostat at 55°F while traveling away from home during the study period, and one participant’s circuit board unexpectedly failed. 

Meanwhile, in Lisbon, NY, the homeowner set the thermostat to 65°F and their heat pump kept the indoor temperature at a comfortable 66.9°F while it was a -19.5°F air temperature outside. 

Homeowner Testimonial

A participant from Rochester enjoyed the quiet operation and steady temperatures from her heat pump, and she even turned her skeptical father into a believer in heat pumps.

Reliability & Resilience 

During the study, only three homeowners needed to make special comfort modifications for the cold snaps. Two of them used plug-in electric space heaters in particularly drafty rooms. In both of these cases, the homeowners knew there was insufficient insulation in those rooms and the need for supplemental heat was not due to a system failure. In the third case, a participant cited simply using warmer clothes and extra blankets on the coldest days of the study period for added comfort. 

In a Rochester home, the system was accidentally turned off for three hours during a cold weather event. During that time, the indoor temperature dropped to 60°F but returned back to its 68°F setpoint in about one hour after turning the system back on. 

It is also important to note that three homes lost power during the study period, but service was restored before their indoor comfort was affected. 

Confidence Grew as the Winter Got Colder 

At the end of the study, average confidence in heat pumps rose from 4.75 to 4.83 (out of 5), and system performance during the cold snaps actually raised confidence and trust rather than eroding it. Additionally, when comparing their heat pumps to their previous heating systems (seven switched from natural gas, four switched from oil, and one switched from electric resistance heat), the participants rated their heat pumps higher on comfort, noise, and utility bills. They also named specific problems that their old systems couldn’t solve, such as cold rooms over the garage and disruptively loud furnaces, and every participant who completed a final interview gave a 5 out of 5 rating for their likelihood to recommend a cold-climate air source heat pump to others. 

About the Homes 

Homeowners across the State volunteered to participate in the study, showing that heat pumps can handle our winters from the North Country to New York City. 

• Katonah (Westchester) [PDF]: A large 2000s home switched from an oil furnace to two ducted heat pump systems. The house stayed within 2°F of the thermostat setting during the polar vortexes, and the homeowners estimate their heating costs dropped by about half.
• Ithaca [PDF]: A 1900 home was weatherized and switched from gas to a zoned mix of ducted and ductless heat pumps. The homeowner was eager to go electric and reported steady, even heat in every room.
• Amherst [PDF]: A 1950 home replaced an aging gas furnace with a ducted heat pump. They re-used their existing ductwork, and the new system held the house at the owners comfort setting in the mid-60s (Farenheit) all winter.
• Rochester [PDF]: A 1920s home replaced their loud gas furnace with a ducted heat pump. It was Rochester’s coldest winter in 11 years, but still the heat pump kept indoor temperatures within a 3°F range of the thermostat setting.
• Lisbon (North Country) [PDF]: A small ranch built in 2009 replaced an oil furnace with a ducted heat pump system. When outdoor temperatures dropped to -19.5°F, the house stayed at a comfortable 67°F inside, and the home’s solar panels helped keep bills reasonable.
• Port Ewen (Hudson Valley): A 1960s home replaced a broken boiler with six single-zone heat pumps. Each unit has its own outdoor compressor, so the main living space and a short-term rental unit in the same house can be heated independently.
• Potsdam [PDF]: A new tiny home for an elderly relative is heated by one ductless mini-split. It stayed near 70°F inside, even when the North Country’s outdoor temperatures dropped to -19.5°F.
• Rochester: A house from the 1870s installed a ducted unit for the first floor and ductless heads for the second floor where there were no existing ducts. While the homeowners experienced temperature dips, they were due to unexpected equipment issues, not the extreme cold.
• Bronx [PDF]: A 1940s home replaced a gas boiler and radiators with a ductless multi-zone system, which was paid for in full by their utility rebate program. Indoor temperatures matched the thermostat setting all winter, and the owner said they didn’t worry about the house while away on vacation.
• Binghamton [PDF]: A home from the early 1900s installed a ducted multi-zone heat pump. The system held indoor temperatures at 70°F throughout each of the polar vortex events and the homeowner is happy with the bills.
• Tonawanda (Western NYS) [PDF]: A 1950s home re-used existing ducts and added a mini-split head in an upstairs bedroom to replace a gas furnace. The new system kept the house between 60°F and 70°F all winter, and the owner switched to a steady thermostat setting after receiving advice from his contractor.

Footnotes

1. Hank Rutkowski, Manual J Residential Load Calculation, 8th ed., ANSI/ACCA 2 Manual J – 2016 (Arlington, VA: Air Conditioning Contractors of America, 2016).