Most cold-climate heat pumps can run at total capacity until the outdoor temperature gets to about 5 F or below. It will still heat your home at those lower temperatures, but not necessarily keep it as warm as you may typically like. That's where backup heat sources come in.
Most standard heat pumps will function at 100% efficiency until the outside temperature reaches about 40° F. However, when the temperature dips below this, most heat pumps are not able to maintain efficiency. They become much less effective at temperatures between 20° F to 30° F.
For this reason, heat pumps start to lose efficiency at around 40 degrees F and become less efficient than furnaces at around 25 degrees F. Heat pumps continue to be effective at cooling the indoors, even at high temperatures. In the South, it rarely gets below 25 degrees.
Many can run at 100 percent efficiency down to 0°F and at decreased efficiency down into the negatives. As a result, these can work in many cold climates for much of the year with needing any supplemental heat. Mid-level mini splits run at 100 percent efficiency down to 20°F and typically require a base pan heater.
Yes, heat pumps will run for hours and hours in cold weather. If your unit is sized exactly right it will run 24/7 at your design temperature (aka almost the coldest day of the year).
A heat pump is designed to maintain a steady temperature, working gradually and efficiently. Avoid large temperature set backs. If you can't resist adjusting your thermostat, try not to lower the set point by more than 2ᵒC or so in colder weather to minimize significant fluctuations.
Since mini-splits use heat pump technology, they're a viable home comfort option in both cold and hot climates. So the answer is 'no,' you don't have to turn off your mini-split when the weather turns cold.
To maximize heat pump cooling efficiency in the summer, you should never set your heat pump temperature higher than 80 degrees Fahrenheit, which is sufficient on the hottest days of 100-degree weather.
According to Power Save AC, most mini splits can keep functioning even in freezing or extremely hot weather. Still, many operate efficiently only until the outdoor temperatures fall below -15°F (-20°C to -26°C) or rise above 115 degrees Fahrenheit (46°C).
This heating method works incredibly efficiently until the outdoor temperature reaches about 35 degrees. At this point, the heat pump has difficulty extracting enough heat from outside to keep up with the thermostat setting. This is when many people assume it's time for switching their heat pump to emergency heat.
Based on our research, the best cold climate heat pump is Mitsubishi's Hyper-Heating, or H2i. Listed as Mitsubishi's M-Series or P-Series for home installation, these heat pumps maintain their full heating capacity down to 5F, and can produce useful heat down to -13F.
If you aren't getting enough heat from your heat pump, you should check the outdoor unit first and foremost. Is the outside of the unit casing covered in ice? If so, you may have a broken defrost cycle. As the outdoor unit leeches heat from the air, it creates condensation that then freezes on the outside of the unit.
Some heat pumps lose efficiency when outdoor temperatures dip below 32°F, but they won't completely stop working. Like other heating systems, a heat pump's efficiency depends on your thermostat settings. If you want to keep your home toasty during sub-zero temperatures, you'll lose performance capabilities.
Simply put, it means you should never set your thermostat for a temperature more than 20 degrees cooler than the outside air. Why not? Most air conditioning systems can only handle a 20-degree difference between the outside and inside air temperatures.
It's normal for your heat pump to run fairly constantly in the winter time. With low temperatures, your pump will be working nonstop for hours to ensure your home stays warm. But if your heat pump is working overtime in the spring or summer when temperatures are milder, you may have an issue!
What temperature does a heat pump quit working? As long as your house is properly air-sealed and insulated, an air-source heat pump can perform well beyond temperatures of -13 degrees Fahrenheit! Some newer models can handle temps as low as -22 degrees.
During heat waves, experts, including utility companies, recommend keeping your thermostat no more than 20 degrees cooler than the outdoor temperature. For instance, if it's 100 degrees outside, aim to set your thermostat to at least 80 degrees.
Heat pumps do not operate as efficiently when temperatures drop to between 25 and 40 degrees Fahrenheit for most systems. A heat pump works best when the temperature is above 40. Once outdoor temperatures drop to 40 degrees, heat pumps start losing efficiency, and they consume more energy to do their jobs.
A mini split heat pump can “ice up” or “ice over.” It's when water on the coil freezes. Then, it can't draw in heat and circulate it inside your home. The result is a system running in the winter but delivering cold air instead of warmth. The two main culprits here are a dirty coil or a refrigerant leak.
While in heating mode, a heat pump uses outdoor refrigerant coils to siphon the available thermal energy from the air. As it does this, it also draws water vapor, which condenses along with the coil. If the temperature outdoors is below the dew point and the freezing point, the water will freeze on the coil.
Modern mini-split systems often use inverter-driven compressors, which are highly energy efficient and allow for more precise temperature control. This feature is particularly beneficial when the system is left to run continuously, as it can significantly improve the unit's overall efficiency.
Rebate-eligible heat pumps can reach over 400% efficiency in mild temperatures and can maintain well over 200% efficiency even into negative temperatures. This is why turning off a heat pump in frigid temperatures and opting to use a fossil fuel boiler or furnace instead is a mistake.
Your auxiliary heat, or secondary heat source, should come on when your heat pump is struggling to heat your home effectively. The thermostat will trigger auxiliary heat when: The outside temperature is below 40 degrees or a set aux heat trigger temperature. The heat pump is in defrost mode.
Air-source heat pumps are generally more efficient when there's only a slight temperature difference between outside and inside air. That means they may become ineffective when outside temperatures fall to and below -5°C, where the atmosphere's temperature is at or below the freezing point.