Most heat pumps won’t pump any heat once the outside temperature is between 10 degrees Fahrenheit and -20F, depending on the heat pump model.
Many heat pumps stop being 100% effective when the temperature drops to between 50 degrees Fahrenheit and 5F, again, depending on the unit tested.
They begin to lose effectiveness when the outdoor temperature is too low for them to absorb enough heat in the cold outside air.
- At What Temperature Does a Heat Pump Stop Working?
- Standard Heat Pumps vs Mini Split Heat Pumps
- What is a Cold Climate Heat Pump?
- Standard Heat Pumps in Cold Weather
- Mini Split Heat Pumps in Cold Weather
- The Best Heat Pumps That Work Below Freezing
- Heat Pump Efficiency vs Temperature
At What Temperature Does a Heat Pump Stop Working?
Between 10 degrees Fahrenheit and -20F.
For a heat pump in cold weather, it isn’t a Working vs Not Working issue.
It is a spectrum.
Some heat pumps begin to lose heating effectiveness in outside air of about 50F. For others, the decline doesn’t happen until the temperature is below freezing.
Heat pumps that work below freezing tend to be mini split heat pumps that are very efficient – those with a high HSPF rating, which is the heating seasonal performance ratio. The HSPF ratio measures how efficiently the heat pump uses electricity to circulate refrigerant, bringing in heat from outside and releasing it indoors.
Standard Heat Pumps vs Mini Split Heat Pumps
All mini split heat pumps work in very cold weather. Only a few standard split system heat pumps work in temperatures below freezing.
The key difference is whether they are inverter-type heat pumps. All mini splits use inverter-driven variable capacity compressors to cycle refrigerant.
Only the top-of-the-line standard heat pumps are inverter driven. This technology is discussed in detail below.
Heat Pump Effectiveness in Low Temperatures
Standard Heat Pumps
|Outdoor Temperature||Heating Capacity (Non-inverter)||Heating Capacity (Inverter)|
|47F||85% – 100%||Up to 120%|
|17F||20% – 35%||50% – 72%|
|5F||0% – 20%||33% – 45%|
|-15F||0%||0% – 20%|
Mini Split Heat Pumps
|Outdoor Temperature||Heating Capacity (Inverter)|
|17F||75% – 100%|
|5F||58% – 100%|
|-15F||24% – 75%|
Why 47F, 17F, 5F and -15F? These temperatures are used in the industry for testing the ability of heat pumps to pump heat in cold weather.
When considering a standard heat pump vs a mini split heat pump in cold weather, let’s look at two American Standard heat pumps – one of each type.
#1: American Standard AccuComfort Platinum 18 4-ton heat pump is a standard split system heat pump for a ducted HVAC system. It does have an inverter-driven compressor.
It provides a maximum of 48,000 BTUs of heat, but:
- 87% or 41,000 BTUs of heat at 47F
- 61% or 28,780 BTUs of heat at 5F
It isn’t rated for use below 5 degrees Fahrenheit.
#2: American Standard / Mitsubishi M-21 H2i Series is also a 48,000 BTU ductless mini split heat pump, also with an inverter-type compressor.
- This heat pump provides 100% of heating capacity at 5 degrees Fahrenheit. In other words, it doesn’t lose any of its ability to capture and transfer heat.
What’s the point? This example shows that “stops working” is a relative idea. Both of the examples are heat pumps that work below freezing. But “work” is a relative term. The mini split “works” much better.
When considering a unit, you have to know that the heat pump is designed for cold climates.
And then you have to get the specific data from the manufacturer or from the Air Source Heat Pump /Northeast Energy Efficiency Partnership or NEEP website to find out how effective it is in cold climates.
What is a Cold Climate Heat Pump?
They are heat pumps that work below freezing. They will supply some or all of their capacity based on design and efficiency.
They are also called cold climate air source heat pumps, or ccASHPs. The term “air source” means that they draw heat out of the air outside, not the ground or a water source as geothermal / ground source heat pumps do.
The US Department of Energy says that “Cold climate ASHPs can reduce household energy consumption by up to 40%, with homeowners currently utilizing electric resistance (e.g., baseboard heat) or fuel oil to heat their homes likely to see the most cost savings.”
Standard Heat Pumps in Cold Weather
Standard heat pumps or split system heat pumps that use an air handler and ductwork indoors are less efficient as a whole and don’t provide the same level of heating in very cold temperatures.
One of the ways they make up for this is through the use of electric heat strips installed in the air handler. These heat strips range in capacity from 5kW to 20kW.
When the standard heat pump begins to lose efficiency and effectiveness, the electric heaters start. And they provide extra heat to make up for the shortcomings of the heat pump.
- 5 kW = 17,050 BTUs
- 10 kW = 34,100 BTUs
- 15 kW = 51,150 BTU
- 20 kW = 68,200 BTU
Mini Split Heat Pumps in Cold Weather
Mini split heat pumps do not rely on electric backup heating strips.
They are much more efficient than standard split systems and can pull heat from outside air at much lower temperatures. Typically, mini split heat pumps become ineffective somewhere between 15F to -15F, a much lower range than standard split system heat pumps.
Here are a few examples from popular brands. Data is supplied by NEEP Product Database of more than 38,700 of heat pumps.
In this table, the Fujitsu and Daikin heat pumps are mini split system heat pumps. For comparison, the Lennox is a standard split system heat pump. All use inverter-driven technology and are 2-ton heat pumps with rated capacity of around 24,000 BTU.
Notice that the Fujitsu and Daikin heat pumps can deliver more heat than they are rated for at 47F. That is because of their super-high efficiency levels.
Can a Heat Pump Work in Cold Weather?
Fujitsu Halcyon 24RLXFZ:
|Outdoor Temperature||Heating Capacity|
Daikin MXL Aurora:
|Outdoor Temperature||Heating Capacity|
|Outdoor Temperature||Heating Capacity|
The Fujitsu heat pump stops working somewhere below -15F. The Daikin heat pump stops working before it gets that cold – it isn’t rated to work in temperatures below 5F. Nor is the Lennox heat pump.
Note that the Lennox heat pump can produce more heat at 17F than at 47F. That seems “impossible” until you look at the amount of electricity used at those two outdoor temperatures. The electrical draw is 1.64 kW when tested at 47F. And it is 2.18 kW at 17F, or 33% higher. So, the unit is less energy efficient at 17F. Now, that makes sense.
The Best Heat Pumps That Work Below Freezing
It won’t surprise you at this point that the best heat pumps for cold climates are those with an inverter-driven refrigerant system. This has been confirmed by many studies including one completed in 2018 by the Minnesota Center for Energy and Environment.
Instead of turning on or off, as in a single-stage heat pump, or running at low or high in a 2-stage heat pump, they vary from 25% to 100% of capacity. They run at just enough capacity to deliver the needed heat without wasting energy.
Some standard split system heat pumps and all mini split heat pumps use inverter-driven technology. Liam McCabe of Consumer Reports gives more details on the value of this technology. “The key feature in a cold-climate heat pump is a variable speed compressor, powered by an inverter. This kind of compressor…enables a single heat pump to work efficiently and effectively in the deepest freeze of winter [and] the most oppressive summer afternoon.”
After a detailed and lengthy analysis of inverter-driven heat pumps, the Office of Energy Efficiency & Renewable Energy of the DOE concluded that “All [inverter-driven] heat pumps were seen to provide useful heating at subzero (Fahrenheit) temperatures…” though results varied significantly by brand and outdoor temperatures.
Heat Pump Efficiency vs Temperature
Efficiency is reduced as the temperature drops. The drop is more severe in cold weather for standard split system heat pumps, especially those that do not have an inverter-style compressor.
COP in a heat pump is the Coefficient of Performance. It measures how much heating the heat pump provides from the amount of electricity it uses. COP is the heating output divided by the energy input, or:
COP = Heating BTUs / Energy Used
COP is a key measurement of heat pump efficiency.
A COP of 3.0 means that the heat pump delivers 3 times more heat energy than the energy it took to gather that much heat by cycling refrigerant from the outdoor component to the indoor unit.
Or, you could say that you get the same amount of heat for 33.3% or one-third of the electricity used.
COP goes down as the outside temperature drops. Here are averages for all heat pumps. Some mini splits outperform this chart.
Ambient Temperature and COP
|70F||3.9 – 4.8|
|60F||3.9 – 4.8|
|50F||3.7 – 4.4|
|40F||2.8 – 3.7|
|30F||2.6 – 3.3|
|20F||2.0 – 2.8|
|10F||1.6 – 2.5|
|0F||1.0 – 2.3|
|-10F||.5 – 2.2|
|-20F||0 – 1.3|
For an example, consider the Daikin Aurora heat pump listed above.
Here is the COP range at different temperatures depending on the rate at which the converter compressor is running.
Daikin MXL Aurora
|Outdoor Temperature||Heating COP Min. / Max.|
|47F||3.4 to 5.14|
|17F||2.55 to 3.88|
|5F||2.17 to 3.31|
COP varies at any temperature because of the variable capacity compressors these units are fitted with. The highest COP – the most efficient operation – is at the lowest compressor speed.
Do heat pumps work below 20 degrees?
Yes, most will gather some heat. How much they will heat depends on the type of system, its compressor type and the design of the individual heat pump.
As noted, standard heat pumps often have backup or auxiliary heating strips in the air handler to supply additional heat when needed. In most standard split systems, the backup heating will be required when outdoor temperature is below 20F.
The heat pumps that work the best below 20 degrees are efficient inverter-driven heat pumps. Some can produce 100% of their rated capacity at that temperature.
Does it make sense to choose a heat pump in cold weather climates?
Yes. A heat pump can be a good choice for freezing winters if it is designed for them. There are quite a few heat pumps that work below freezing – many are mini split heat pump systems, but there are a few standard heat pumps known as cold climate air source heat pumps.
At what temperature does a heat pump stop working?
It varies by model, but it’s around 0 degrees Fahrenheit for most. This graph, for example, shows that Rheem’s most efficient 2-ton standard heat pump puts out less than 5000 BTU of heat at -10F.
But the Fujitsu Halcyon heat pump discussed above can pump roughly half of its rated capacity at 15 degrees below zero Fahrenheit.
What are the best heat pumps for cold climates?
Inverter driven heat pumps. Especially mini split heat pumps with inverter-type compressors.