How Does Heat Pump Work in Cold Climate
Heat pumps are one of the most efficient methods for both heating and cooling homes in various climates. But can heat pump systems still operate in temperatures below 20 degrees Fahrenheit (about -6.7 degrees Celsius)?
Contrary to common belief, modern cold climate heat pumps can effectively provide heating for homes even when temperatures drop below -10 degrees Celsius (14 degrees Fahrenheit). Even at these low temperatures, the best cold climate heat pumps are still more energy-efficient compared to furnaces and boilers.
One only needs to ask the millions of homeowners on the Scandinavian Peninsula to understand this. The installation rate of heat pumps in Norway, Finland, and Sweden is faster than anywhere else in Europe.
You might think, “Scandinavians seem to do everything better than the rest of the world.” However, some states in the United States actually have adopted heat pumps at a faster rate than the countries listed above, even including some of the coldest climate regions.
Last year, in the state of Maine, 50 units per 1,000 households were sold, slightly higher than the leading European country, Norway. In contrast, other regions in the United States sold 23 units per 1,000 households.
Compelling evidence suggests that heat pumps can also save most homeowners a significant amount of money. Data from NREL’s ResStock model reveals how much money regular homeowners in different states can save by switching to heat pumps. For instance, in Maine, the average homeowner can save $718 per year.
In the cold and populous state of New York, the average homeowner can save $637 annually. Millions of homeowners in this state who use oil for heating can save $976 per year.
Pennsylvania: $935. Massachusetts: $838. Ohio: $676. You get the idea. In regions with many cold areas, using heat pumps is the most cost-effective way to heat homes while saving money in the process.
Three Myths About Cold Climate Heat Pumps
But why do many contractors and homeowners still believe that heat pumps are ineffective in cold climates? My theory is that three myths are to blame:
Capacity Myth: Heat pumps can’t generate enough heat to keep your home comfortable in cold weather.
Efficiency Myth: Heat pumps lose their efficiency advantage as temperatures drop.
Cost Myth: Heat pumps are too expensive to operate in cold weather due to lower efficiency.
It’s important to clarify that these are all myths. However, like many lies, they have roots in truth. Sometimes, heat pumps’ capacity might not match a home’s load, making them inefficient for certain climates and homes.
In the rest of this article, I aim to debunk these myths and delve into why some heat pumps work in cold climates while others do not.
How Do Heat Pumps Work in Winter?
Before we dive into dispelling these myths, it’s helpful to understand the basics of how heat pumps work in cold weather.
Unlike traditional heating methods like furnaces or electric baseboards, heat pumps don’t directly produce heat by burning fuel. Instead, they use a small amount of energy to run a compressor, effectively transferring heat from one place to another.
Even on cold days, the outside air contains some heat, albeit not apparent at first. Heat pumps absorb this heat and transfer it into your home.
This fundamental principle enables heat pumps to take one unit of energy (in the form of one watt of electricity) and pump out three or four units of heat (usually measured in British Thermal Units or BTUs). More technically, using a bit of energy to run the compressor, heat pumps can achieve a coefficient of performance (COP) greater than 1.
Key points to note are:
Even on cold days, the outside air contains energy.
Heat pumps bring this energy into your home.
The result is a highly efficient heating system.
With this understanding, let’s start debunking the myths.
Capacity Myth
The first myth to debunk is the “Capacity Myth,” which claims that heat pumps lack the capacity to provide sufficient warmth for homes on cold days.
Earlier, I mentioned two terms: load and capacity. To understand why the “Capacity Myth” is untrue, it’s helpful to grasp these two concepts.
A home’s heating load refers to the energy required to maintain the home at a comfortable temperature. The load changes with temperature fluctuations. On a sunny 70-degree day, the load is essentially zero. On colder days, this value becomes much higher. Your heating system has to work harder to keep your home comfortable.
The load also depends on unique characteristics of the home, such as the amount of insulation or the type of doors and windows. An 1850s house without insulation will require more energy than a brand-new house. The load is just a technical way of describing and measuring all of this.
Capacity refers to the amount of heat (or cooling, in the case of air conditioning) an HVAC system can provide. If the load is the leakage at the bottom of a bucket, then capacity is the faucet pouring in more water.
Unlike other HVAC systems, heat pumps don’t have a fixed capacity. For instance, a furnace might have a fixed capacity of 100,000 BTUs every day of the year, regardless of the weather, while a heat pump’s capacity might range between 40,000 and 60,000.
This makes sense when you think about it. I mentioned earlier that heat pumps effectively capture heat from outdoor air and transfer it indoors. The colder the temperature, the less energy is available to capture. As a result, capacity drops.
As long as capacity doesn’t fall below the load, heating will work fine. But if a contractor undersizes the system, your house might feel uncomfortably cold on cold days. In the example above, this might happen at around -7 degrees Celsius (19.4 degrees Fahrenheit).
At that point, your house doesn’t instantly turn into a refrigerator. No, the backup heat strip kicks in, essentially turning your heat pump into a space heater. This method isn’t as efficient as the compressor, but since backup heat is used for less than 1% of the year on average, it doesn’t significantly impact operating costs.
In home energy, very few things are black and white. In a leaky house, a low-capacity heat pump won’t cut it. And if you live in a place that regularly drops below -22 Fahrenheit (about -30 Celsius), even a good heat pump might not handle all the heating load; this is where the best cold climate heat pumps shine.
But for the vast majority of Americans, heat pumps can deliver 100% capacity, keeping their homes comfortable year-round. Most complaints about heat pumps not working in cold weather stem from user errors (often by installers), not underlying technology.
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Efficiency Myth
I previously mentioned the wonder of heat pumps converting one unit of energy into three or four units of heat. However, this ratio (known as the coefficient of performance or COP) isn’t a fixed number.
The colder it is outside, the harder it is for a heat pump to efficiently extract heat from the air and transfer it into your home. So, as temperature drops, COP drops.
But a common misunderstanding—the “Efficiency Myth”—is that COP drops below 1 at around 30 or 40 degrees Fahrenheit (about -1 to 4 degrees Celsius). If true, this would mean you need 1 unit of energy to produce only 0.8 units of heat. At that point, running resistive heaters or gas furnaces might make more sense, as these systems can convert 80-100% of their energy into heat.
However, this isn’t the case. Modern cold climate heat pumps, compared to their predecessors, can achieve COPs above 1 even in extremely cold temperatures. Many of them achieve COPs between 2 and 3 at temperatures around 30 or 40 degrees Fahrenheit.
The graph below shows the COP of a Mitsubishi cold climate heat pump during a series of tests conducted in Alaska. As you can see, the COP generally remains above 1 until around -10 degrees Fahrenheit (about -23 degrees Celsius).
In other words, the efficiency of this heat pump is higher than any other system until the temperature reaches -10 degrees Fahrenheit.
So, until the temperature drops to -10 degrees Fahrenheit, this heat pump’s efficiency is better than any other competing system. How many hours per year do temperatures in your region drop below -10 degrees Fahrenheit?
Conclusion: Even in extremely cold weather, today’s heat pumps are the most energy-efficient way to heat homes.
Cost Myth
Most people are not concerned with BTUs and COPs. They want to know how much something costs in dollars.
This is where all these comparisons become a bit tricky. Energy prices in the United States vary widely depending on where you live. In Connecticut, electricity costs a little over 20 cents per kilowatt-hour. In Louisiana, the same electrons cost 10 cents per kilowatt-hour.
Natural gas follows a similar range. In Florida, residential natural gas costs around $2 per unit. In Idaho, it’s 65 cents per unit. Furthermore, every climate and home is different. Everyone needs a different amount of energy to stay warm in the winter.
Estimating the cost for each household in the U.S. using different fuels and equipment requires supercomputers that handle millions of data points. Fortunately, these exist.
In 2017, the National Renewable Energy Laboratory (NREL) embarked on a quest to find the best energy efficiency opportunities for every single-family home in the U.S. After about a year of data collection, they plugged this data into algorithms. One of the most powerful computers in the nation spent around 9 months doing all the calculations.
This monumental effort allowed researchers to understand how much money regular homeowners could save each year by switching to more efficient heating equipment. So, what did they find?
For the vast majority of the country, heat pumps are the most cost-effective way to heat homes.
The most relevant point here is that even in cold climates, heat pumps can save people hundreds or even thousands of dollars annually, effectively dispelling the myth that heat pumps are too expensive to use in cold climates.
Similarly, here are some savings that typical homeowners in cold climate states can expect:
The only places where people might not save money by switching to heat pumps are:
If they are transitioning from a gas furnace and natural gas is significantly cheaper.
If natural gas is much cheaper than electricity in their area.
However, if you spend a substantial amount on heating your home each year, whether you’re in Florida or Maine, heat pumps are likely to save you money. If you currently use standard electric, oil, or propane systems for heating, it’s almost certain that you’ll save money.
Over time, these savings are expected to increase. Many energy analysts anticipate that as governments begin to price carbon pollution and utilities build more cheap renewable power, natural gas prices will rise, and electricity prices will fall. Meanwhile, heat pumps’ efficiency continues to improve, reaching theoretical maximum efficiency.
This means that not only can today’s heat pumps work in cold climates, but they will work even better in the future.
Frequently Asked Questions
Can heat pumps work below 20 degrees Fahrenheit?
Yes, even when temperatures drop below -10 degrees Fahrenheit, modern cold climate heat pumps can effectively provide heating for homes. At these temperatures, the best cold climate heat pumps are still more energy-efficient than furnaces and boilers.
At what temperature do heat pumps stop working?
The best cold climate heat pumps can operate effectively at temperatures around -10 degrees Fahrenheit. Many of these heat pumps come with backup heating elements that kick in at temperatures below this point to maintain indoor warmth.
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