January in a northern climate is when my inbox gets loud. The pattern repeats: a homeowner or facility manager has a heat pump that has been running since 2 a.m., the air from the vents feels lukewarm, and the thermostat keeps showing auxiliary heat. The conclusion is usually the same: this heat pump can’t handle real winter, and it needs to be replaced.
I see that from the other side of the counter. My job is quality and brand compliance for GREE’s commercial heating and cooling lines. I review units before they ship, and I read field reports when they come back. In my experience, most of those can’t-handle-winter verdicts are wrong. The machine is usually fine. The expectation is what needs replacing.
How does a heat pump work, really?
A furnace makes heat. A heat pump moves heat that is already in the outdoor air. Refrigerant absorbs that heat, the compressor compresses it to a higher temperature, and the indoor coil releases it into your space. Reverse the cycle and you get cooling. That one paragraph is the whole concept.
Winter makes the job harder in two directions at once. As outdoor temperature falls, there is less heat for the outdoor coil to collect. At the same time, your building is losing heat faster. So the heat pump’s output drops exactly when your heating load climbs. That is physics, not a manufacturing defect.
The industry has changed faster than most advice columns have. Older fixed-speed systems often gave up below about 40°F and switched over to backup heat. Inverter-driven compressors and enhanced vapor injection changed that. Some current systems—including GREE’s low-ambient heat pump line—keep producing heat down to -25°C, which was unthinkable a few years ago. What was best practice in 2020 may be outdated in 2025. Even so, no heat pump should be operated like a gas furnace. If you do, it will underperform.
Why the thermostat is the real suspect
Most heating complaints are not about the heat pump losing capacity. They are about the thermostat making decisions that defeat the heat pump.
Here is the pattern I see in service logs, winter after winter: someone sets the heat pump back by 6 or 7 degrees overnight, the way they used to do with a gas furnace. In the morning, the thermostat sees a large gap between room temperature and the setpoint. To close that gap quickly, it energizes auxiliary heat—usually electric resistance strips in the indoor unit. The strips run for a long time, the compressor barely gets used, and the energy bill climbs. The homeowner concludes the heat pump is weak. The system was never allowed to do its job.
A heat pump is most efficient when it runs steadily. Large setbacks do not save energy the way they do with a furnace. So the first rule is simple: pick a temperature and leave it alone, or use a small setback of about 2 degrees.
So when someone searches GREE thermostat how to use, I hope they find this: the important settings are in the installer menu, not in the phone app. System type, balance point, and auxiliary heat lockout matter far more than scheduling. Configure the system for heat pump operation and set the lockout so the backup heat only comes on when the outdoor temperature is genuinely too low for the compressor to keep up.
The same logic applies if you are using a universal thermostat. A Honeywell Home thermostat is a capable piece of equipment, but it has to know it is connected to a heat pump. That means putting it into heat pump mode and setting the O/B terminal to match the reversing valve. Configure it as a conventional furnace and the system can blow cool air in winter while the outdoor unit runs perfectly.
This is where I admit my own mistake. In late 2022, I approved a warranty repair for a heat pump that was running nonstop and blowing cool air. The service notes suggested a reversing valve failure, so I authorized the replacement part without asking for the thermostat configuration history first. The technician arrived, checked the thermostat, and found the real problem: it was configured as a conventional furnace. The compressor was fine. The valve was fine. I converted a setup error into an unnecessary repair. Now I do not approve compressor or valve work on a cold-weather complaint until someone has pulled the thermostat logs.
The 12,000 BTU trap
The second reason good equipment gets blamed is sizing. People choose systems by the number on the box, and they assume that number means the same thing in every condition.
Take the GREE Bora A4 Silver 12000 BTU as an example. It is a one-ton class split system, and 12,000 BTU per hour is its nominal capacity. Nominal is the key word. That figure comes from a specific rating condition, not from every possible outdoor temperature and building load.
In North America, air-source heat pump heating capacity is measured under AHRI Standard 210/240, typically at 47°F and 17°F outdoor conditions. When you compare models, compare them at those points. But even that does not tell you whether the unit is right for your building. That requires a load calculation—the Manual J method in residential practice, or a proper engineering heat-loss study for commercial space.
An undersized unit will run forever and still lose ground on the coldest nights. An oversized unit short-cycles, dehumidifies poorly, and wears out faster. The cure for both is correct sizing, not a bigger model number.
What misdiagnosis actually costs
Here is what those mistakes cost. Resistance heat converts electricity to heat at roughly one-to-one. A heat pump can deliver two or three times that amount per unit of electricity, depending on outdoor conditions. Every hour spent on backup heat instead of the compressor is efficiency lost. The bill is where it shows up.
Premature replacement is a larger cost. I have reviewed warranty cases where the recommended fix was a whole new outdoor unit, and the actual cause was thermostat configuration, a dirty filter, or low refrigerant charge. Replacing the unit fixed the symptom only because it came with a fresh setup. That is an expensive way to solve a settings problem.
There is also self-inflicted winter damage. The week after heavy snow, we see heat pump coils with the fins flattened. The culprit is often a shovel or an electric snow blower used to clear snow off the unit. Crushed fins restrict airflow, pressures climb, and the system runs as if it is failing. The unit was not defective. It was damaged by a tool that belongs on the driveway, not at the condenser. Clear a path around the unit, and brush the cabinet gently if needed, but do not aim a snow blower at the coil.
Before you replace anything, check these five things
Here is the short list I use when a heat pump complaint reaches my desk:
- Use the thermostat in a way that respects heat pumps. Keep setbacks small or use a schedule designed for heat pumps.
- If your system has a GREE thermostat, go through the installer settings and set balance point and auxiliary heat lockout. If you have a Honeywell Home thermostat, confirm it is configured for heat pump operation with the correct O/B setting.
- Compare the building heating load to the unit’s actual heating capacity at low outdoor temperature—not to the 12,000 BTU label.
- Check the basics: clean filter, clear outdoor coil, unobstructed airflow. Keep the snow blower away from the unit.
- If someone recommends a replacement, ask to see thermostat history and supply-air temperature readings first. If they have not checked those, the diagnosis is incomplete.
Quality people do not promise that nothing will ever break. Refrigerant leaks, failed capacitors, and bad fan motors all happen. But the majority of winter heat pump complaints I review are not hardware failures. They are failures of expectation, configuration, and sizing. That is good news, because those can be fixed for far less than the cost of a new system.
Before you blame the cold, check how the system is being controlled. In most cases, the heat pump wasn’t broken. It was just never given a fair chance.
