Ten years ago a heat pump in Pennsylvania was unusual outside of houses with no gas service. Now we see them going into new construction across the state and replacing electric resistance heat in older homes.
They also generate more worried phone calls per unit installed than anything else we service, because much of their normal cold-weather behaviour looks like a malfunction to anyone used to a furnace.
What a heat pump is doing
A furnace burns fuel to create heat. A heat pump does not create heat at all — it moves it, running refrigeration in reverse to collect warmth from the outdoor air and release it indoors. Even air at 20°F contains usable heat energy.
Because it moves heat rather than making it, it can deliver more heat energy than the electrical energy it consumes. That is where the efficiency comes from. It is also why performance changes with outdoor temperature: the colder it is outside, the less heat there is to collect and the harder the system works for each unit of it.
Normal behaviour that alarms people
The air feels cool
This is the complaint we get most. A furnace delivers short bursts of air at maybe 120°F. A heat pump delivers a much larger volume of air at something closer to 95°F.
Ninety-five degrees is warmer than your house. It is also cooler than your skin, so standing under a register it feels like a draught. The house still reaches temperature; it does so gradually and steadily rather than in bursts. Nothing is wrong.
It runs for a very long time
Long, steady run cycles are how heat pumps are supposed to work, particularly variable-speed models that modulate rather than switching fully on and off. A heat pump that cycles on and off briefly in cold weather is more likely to have a problem than one that runs continuously.
It stops heating, the outdoor fan cuts out, and it steams
That is the defrost cycle. Moisture condenses and freezes on the outdoor coil as it pulls heat from the air, so periodically the system reverses briefly to melt that frost off. It lasts a few minutes, often produces visible steam, and during it the indoor air may feel cool — which is why many systems run backup heat to cover the gap.
Startling the first time you see it. Entirely normal.
Some frost on the outdoor unit
Expected between defrost cycles in cold, damp weather.
What is actually a fault
The unit is encased in ice
Light frost clears itself. A solid shell of ice over the coil, or ice built up around the fan and base, means defrost is not working — a defrost board, sensor or thermostat problem, a reversing valve that will not switch, or a refrigerant charge issue.
Do not chip at it. The coil fins and refrigerant tubing damage very easily and turn a control repair into a sealed-system repair. Switch the thermostat to emergency heat and call.
Auxiliary heat is on when it is not that cold
Nearly every Pennsylvania heat pump has backup heat — usually electric resistance strips, sometimes a gas furnace in a dual-fuel arrangement. It exists to help in genuinely cold weather.
If your thermostat shows auxiliary or emergency heat running at 40°F, the heat pump is not carrying its share. That is worth investigating, because resistance heat is expensive and the usual causes — low refrigerant charge, a failed outdoor fan, a stuck reversing valve, or a thermostat misconfigured after a replacement — are all fixable.
The clearest signal is your electricity bill. A winter bill that has jumped sharply with no change in habits usually means strip heat is doing work the heat pump should be doing.
It cools in summer but will not heat in winter
That specific pattern points at the reversing valve or its solenoid — the component that decides which way heat moves.
The honest version of the cold-weather question
People ask whether heat pumps work in Pennsylvania. The answer depends entirely on which heat pump.
An older single-stage unit loses capacity fairly steeply as the temperature falls and hands over to backup heat somewhere around freezing. Through a Pennsylvania January that means a lot of resistance heat and a painful bill. This is where the reputation came from, and for that equipment the reputation is fair.
Modern variable-speed cold-climate units are a different machine. They hold useful capacity well below freezing and lean on backup only during genuine cold snaps. In this climate they work, and for a house currently on electric baseboard they are usually a substantial improvement.
If your existing heat pump is struggling, the useful order of operations is to rule out a fault first. Low refrigerant charge produces exactly the same symptom as an undersized or outdated system, and it is a great deal cheaper to fix.
Looking after one through a Pennsylvania winter
- Keep roughly two feet clear around the outdoor unit, including through snow. It needs airflow all winter, unlike an air conditioner.
- Make sure it is not under a roofline that dumps snow or drips meltwater onto the coil — meltwater refreezing is a common cause of serious icing.
- Leave the thermostat alone. Deep setbacks backfire: recovering several degrees triggers expensive resistance heat. Heat pumps prefer a steady setting.
- Use emergency heat only as a stopgap when the heat pump is iced or broken. It switches the heat pump off entirely and runs the costly backup alone.
- Change filters. Airflow matters more on a heat pump than on a furnace, because it is working with smaller temperature differences.
If something looks wrong and you are not sure whether it counts as normal, call and describe it. We would rather talk you through a defrost cycle for free than have you sit in a cold house assuming it is supposed to be like that.