Key takeaways
- Cold-climate heat pumps are built to keep heating below freezing.
- Efficiency and output drop as it gets colder, and backup heat fills the gap.
- Dual fuel pairs a heat pump with a furnace and switches between them by outdoor temperature.
- Duct leaks, air leaks and insulation affect results as much as the unit does.
What happens to a heat pump as it gets colder
A heat pump pulls heat from outdoor air, and there is less of it to pull when the temperature falls. Two things change at once. The unit produces less heat, and it uses more electricity for each unit of heat it delivers. At the same time, your house loses heat faster, so it needs more.
The outdoor temperature where the heat pump's output exactly matches the house's heat loss is the balance point. Above it, the heat pump carries the load alone. Below it, something else has to supply the rest, or the heat pump runs constantly and the house slowly cools.
That is not a flaw. It is how the equipment is designed, and a good contractor plans around it.
Cold-climate heat pumps
Older heat pumps had a poor reputation in cold places because they lost output quickly and leaned on electric resistance strips, which are an expensive way to make heat. Newer cold-climate models are different. They typically use variable-speed compressors and improved refrigerant circuits that let them keep heating at much lower outdoor temperatures.
If you are comparing models, look at the manufacturer's low-temperature performance data, not only the efficiency rating, which is measured under milder conditions. Ask a contractor how a unit performs at the cold end of Southwest Ohio winters.
Sizing matters. A unit sized from a load calculation for your actual house will outperform one chosen by rule of thumb. Oversizing does not improve winter performance and can cause short cycling in spring and fall.
Backup heat and emergency heat
Most ducted heat pumps include backup heat for the coldest hours. It is usually electric resistance strips in the air handler, or a gas furnace in a dual-fuel setup. The thermostat or control brings it on when the heat pump cannot keep up, or during a defrost cycle so cold air does not blow from the vents.
You may also see an emergency heat setting. It shuts off the heat pump and runs only the backup heat. Use it if the outdoor unit fails or is buried in ice and you are waiting on service, not as a regular setting.
If the backup heat seems to run all the time in moderate weather, something is off. Common causes include a thermostat setting, a low refrigerant charge, a dirty coil or a failing component, and that is a call for a professional. A heat pump service visit can sort out which it is.
Dual fuel for the coldest days
A dual-fuel system pairs a heat pump with a gas furnace. Above a set outdoor temperature, the heat pump does the heating. Below it, the furnace takes over. Many Southwest Ohio homes already have natural gas and a furnace, so adding a heat pump to a furnace in good shape is a common upgrade.
The switchover temperature is set by your contractor and depends on the equipment, local energy rates and how your house performs. It can be changed later if the first setting is not right. The system needs a compatible thermostat or control, and the furnace should be inspected each year for safe venting and a sound heat exchanger. Gas heating problems, including any suspicion of carbon monoxide, need a professional right away.
Is your house ready for a heat pump
Many homes in the region are older, with plaster walls, original windows and ducts running through unheated basements or attics. Those houses lose more heat, and leaky ducts waste a lot of what the system produces.
Before choosing equipment, have someone check the ductwork, the insulation levels and the air leaks. Sealing and insulating ducts, and air sealing the attic and rim joists, can lower the load enough that a smaller heat pump does the job. If the house has no ducts or the existing ducts are poor, a ductless mini-split can heat the rooms you use most. See ductwork for what is involved in repairs and sealing, or contact us to talk through your house.
Frequently asked questions
At what temperature does a heat pump stop working?
There is no single temperature. Output and efficiency fall gradually as it gets colder, and each model has its own limits. Cold-climate models keep heating well below freezing, and backup heat covers anything beyond that.
Do I need to keep my furnace if I add a heat pump?
Not always. Some homes run a heat pump with electric backup, and others keep a good furnace for dual fuel. The right choice depends on the house, the furnace's condition and your energy rates.
Is it normal for my heat pump to blow cooler air than a furnace?
Yes. A heat pump delivers warm air at a lower temperature than a gas furnace, but it runs longer to make up for it. The air should still feel warm, not cool, at the vents.
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