Yes, and it stopped being a real question about a decade ago. The useful question is narrower: at what outdoor temperature does your specific system stop keeping up, and what happens when it does.
The reputation comes from real equipment. Heat pumps sold in the 1980s and 90s were single-stage machines that lost most of their output by the time it hit 20°F, at which point electric strip heat took over and the bill tripled. People remember that. It was a fair complaint about a machine that no longer exists.
What changed is the compressor. Variable-speed inverter compressors can spin faster as it gets colder, partly offsetting the falling capacity, and vapor injection lets a unit extract useful heat from air that a 1990s machine would have given up on. A current cold-climate model holds most of its rated capacity at 5°F and still produces heat at -13°F.
Every heat pump produces less heat as it gets colder, because there is less heat outside to collect. Meanwhile your house needs more. Those two lines cross somewhere, and that crossing point is the whole ballgame.
Your balance point is the outdoor temperature where the heat pump's output equals your house's heat loss. Above it, the heat pump carries the house alone. Below it, something else has to make up the difference.
A well-designed system in a reasonably tight house lands its balance point somewhere between 5°F and 20°F. If your winter design temperature is 10°F and your balance point is 15°F, the gap is a handful of hours a year, not a season. If your balance point is 35°F, something is wrong with the sizing or the envelope, and you will feel it on the bill.
Electric strip heat runs at exactly 100% efficiency, which sounds fine until you compare it to the 300% the heat pump was managing a moment ago. Running strip heat costs roughly three times as much per unit of heat. Used for thirty hours a year it is invisible. Used for three hundred, it is the reason someone tells you heat pumps are expensive.
Three configuration mistakes cause most of that overrun, and none of them are the equipment's fault:
Cold-climate monitoring programs in Maine, Minnesota, and Vermont have tracked hundreds of installed systems through real winters. The pattern is consistent: the equipment performs close to its published curves, occupant satisfaction is high, and the households that saw disappointing bills almost always had an identifiable cause, undersized equipment, leaky ducts, or backup heat running when it should not have been.
Which is the honest summary of the whole question. The machine works below freezing. Whether your installation works below freezing depends on the load calculation, the ductwork, and the controls, and all three are decided before anyone turns it on.
