The Build Review’s Associate Author Matt Ferrell discusses the Truth About Heat Pumps and Cold Weather. Heat pumps are versatile, efficient, and great for both heating and cooling … or are they? Whenever heat pumps are mentioned, critics bring up their ineffectiveness in cold weather, so is that still true? Or do more modern heat pumps continue to work effectively in cold climates? The arguments against the “heat pump all the things” attitude appears to have some truth (at least on the surface). Should you really be pumped for heat pumps or is it all a bunch of hot air?
YouTube Video Transcript:
Heat pumps are versatile, efficient, and great for both heating and cooling … or are they? Whenever heat pumps are mentioned, critics bring up their ineffectiveness in the cold, so is that still true? Or do more modern heat pumps continue to work effectively in cold climates? I’m currently building a new home that’s going to have a geothermal heat pump system for heating and air conditioning and I live in an area that can get pretty cold in the winter. Needless to say, I have a personal interest in this topic. The arguments against the “heat pump all the things” attitude appears to have some truth (at least on the surface). Should you really be pumped for heat pumps or is it all a bunch of hot air?
What’s a Heat Pump and Why You Should Want One
I’ve said in previous videos that we should heat pump all the things. Thankfully, heat pumps are finally starting to hit the mainstream. Today, worldwide sales of heat pumps are set to soar to record levels as the global energy crisis accelerates their adoption and governments incentivize their use. I remember when I was a kid my parents downplaying getting a heat pump for our house because “they don’t work well in the cold.” It’s been a common belief for a long time that doesn’t seem to want to go away. However, there are promising new models of heat pumps hitting the market with performance that challenges that notion. I’ll get to those details in a minute, but for context let’s briefly recap what a heat pump is and how they work.
A heat pump is really just a refined series of heat exchangers. When it’s hot out, it works similar to your average air conditioner. The indoor coil is filled with a working fluid cooler than the ambient temperature of your house. The hot indoor air passes over the cool-fluid-filled coil, allowing our working fluid to “steal” heat from the air and cool your house down. Stealing this heat slightly increases both the temperature and pressure of the fluid. This now warm and slightly pressurized working fluid is then sent through a compressor, which makes it a very hot and pressurized fluid. Next it’s pumped through an outdoor coil where it releases some of its heat back to the outside air, allowing the fluid to cool off and depressurize a little. Finally, the warm and slightly pressurized working fluid goes through an expansion valve, which allows the fluid to return to its original cool and depressurized state, ready to continue back to the indoor coil and do it all again. 1
But unlike your fridge or air conditioner, a heat pump has a reversing valve, allowing it to do the, uh, reverse: pumping heat into your home from outside as well.1 Bringing ambient heat inside even when it’s cold outside might seem counterintuitive. Despite the fact that those cold temps reduce a heat pump’s efficiency, it’s all just physics.2
During the entirety of either process, the heart of the system that we’re actually spending electrical energy on is the compressor, which doesn’t use much energy. The system is just moving preexisting heat around and putting physics to work by compressing a fluid to increase its temperature. It’s much more efficient than burning fuel for heat. In fact, most heat pumps have a Coefficient of Performance (COP) of 2.5,3 making them 3 to 5 times more efficient than the average 95%-efficient gas furnace. COP is the ratio between the heat energy you get out of the system versus the electrical energy you put in. This has the potential to save you approximately $300 or more annually.4 Utilizing local bodies of water for heat pumps, can produce 6x more heat energy than the electrical energy you put into the system. An efficiency close to 600% feels almost like a physics cheat code.5
And the benefits don’t stop there. Heat pumps require less professional maintenance than combustion systems, and have an average lifespan of 15 to 20 years.5 They’re safer than the competition, too, because they don’t burn anything onsite.6
The potential benefits of heat pumps are even more exciting when we look at the big picture. Heating alone accounted for almost half of all final energy consumption in 2021, making it the single largest energy consumer globally.7 Efficiency improvements can make a huge difference here.
Heat Pump Challenges
So, what’s the catch? Despite the minimal operational costs for heat pumps, the upfront installation costs can be hefty.5 According to a study from Poland, one of the fastest growing heat pump market’s, the total cost of ownership for an air-to-water heat pump was estimated at €8,000, or roughly $8,530.8 Compared to the cost of coal stoves at about €1,500 ($1,600), or gas boilers at around €3,000 ($3,200), that’s quite a lot. The higher cost of heat pumps is mostly tied to the installation process, which in some cases can be complicated or disruptive.8 I’m specifically talking about ground source (or geothermal) heat pump systems. It’s the most efficient type of system you can get, but they sometimes require large areas of land to install the underground coils horizontally.9
I’m going through the process of getting a geothermal system installed in my new home and they drilled a vertical well. While space wasn’t an issue by going vertical, there’s still geographical studies that have to be done to figure out the placement and get proper permitting. Thankfully, the existing topographical maps of my property that were done a couple of decades ago were enough.
That brings us to the potential Achilles’ Heel of heat pumps: they don’t work as well in cold weather when you need them most. When the ambient temperature drops to 5 C (about 40 F) or lower, it can mess with the working fluids’ ability to absorb and release heat by affecting its phase change or thermal properties. Basically, it stops working as well. In response, the overall thermal efficiency of the heat pump decreases and electrical power consumption may increase as the pump works harder to achieve heating conditions.1 And at very low temperatures, frost can accumulate over the exterior coil, which further reduces efficiency. This can be overcome if you incorporate a small electric heater into the system, but that comes with additional upfront costs, increased electricity usage, and other complications.
But is that still true with newer heat pump tech? Are heat pumps still worth it?
The Bright Heat Pump Future
In short, yes … but let’s start by busting the big heat pump myth: that heat pumps struggle to pump heat on cold days.
There’s actually plenty of heat pumps already on the market that tackle colder temperatures with style. For instance, Northeast Energy Efficiency Partnerships (NEEP) maintains a database of models that you can buy right now that all perform well in the cold weather typical of the northeastern United States.10 But how did heat pumps overcome their greatest weakness?
The most exciting improvements use innovative compressor tech. Most compressors can only run at 100%, which can cause undue strain running at max power. Since that style of compressor can’t modulate its output for a given thermostat setting, it’s wasting electrical energy switching on and off repeatedly. Imagine you have your thermostat set to 72 F, the system is going to be switching on and off again and again to maintain that temperature. But a variable speed compressor could run at 30% speed to achieve the same temp, which increases the efficiency of the entire heat pump system. If you need more heat, then the pump can just move the working fluid through the system faster.11
Mitsubishi is currently working on an inverter that allows for a process called “flash injection.” This reroutes hot fluid back to an indoor coil to boost heating. Meanwhile, the cold fluid is routed toward the compressor, which helps it cool down. This is especially useful during cold weather, when the compressor has to work extra hard to maintain high-performance heat exchange.12 The efficiency does dip a little in flash-injection mode and it may still have to run the occasional defrost cycle. Even with these additional power-draws, cold climate heat pumps (CCHPs), like this one, still perform more efficiently than an electric-resistance heater or fuel-fired system. 13 The efficiency gain may drop, but it doesn’t stop.
Then there’s a lot of smaller engineering tweaks. CCHPs typically use fluids that have a lower boiling point than their traditional heat pump counterparts. This allows them to continue flowing through the system at low ambient temperatures and draw more heat energy from cold air even when it’s freezing outside.14 Some CCHPs also utilize reduced ambient airflow rates, increased compressor capacity, or other improvements to the configuration of the compression cycle.13 However, there are some negatives to some of these CCHP fluids because they can have a negative impact on the environment if released. Similar to electric motors or other tech I’ve previously covered, there’s all sorts of little optimization tweaks you can make to tailor a device to your needs, so it should be no surprise that there’s a lot of companies working to optimize heat pumps right now.
Here in the US, that’s partially due to the Department of Energy’s Residential Cold Climate Heat Pump Challenge. Launched in 2021, this program encourages companies to develop, test, and commercialize heat pumps to perform beyond current best-in-class products in 5 F to -15 F (or -15 to -26 C) weather.15 These companies have kept their innovative techniques close to the chest, but their progress has been verified by Oak Ridge National Laboratory and they seem to be on track for the challenge’s end goal of 2024.
For example, Texas-based Lennox was reportedly the first company to develop a prototype to meet the CCHP Challenge, and they did it about a year ahead of schedule! They’re even going to make the jump to commercialisation next year. 16
Then there’s Trane in North Carolina, who announced their CCHP prototype had passed DOE scrutiny last November. Trane’s prototype is especially durable, performing in temperatures as low as -23 F (that’s -30.5 C!) exceeding the DOE temperature requirement. 17
The Florida-based company Carrier celebrated its prototype passing this test in November of last year, and claims their CCHP is designed to communicate with the grid so it can be told to moderate its energy use during peak hours. It uses environmentally-conscious working fluids to boot. Like Lennox, they’re expecting commercialization next year. 18
Finally, Johnson Controls in Wisconsin has built an air-source heat pump prototype for locations with temperatures below -20 F (-29 C). Designed with AHRI Standard 1380 certifications in mind, this is another CCHP that can smartly curtail its energy consumption when during peak hours.19 It’s worth noting that, in addition to their CCHP challenge entry, Johnson Controls already has two heat pumps on the market that meet those previously mentioned NEEP standards. 19
So, the cold isn’t really a problem anymore outside of the most extreme circumstances. This leads us to the second biggest hurdle: that pricey initial investment. Even if a heat pump pays for itself over time, not everyone can afford the start-up costs. Luckily, help is on the way. There are rebates here in the U.S. for heat pump installation packaged as part of the Inflation Reduction Act (IRA). Also, according to the White House, households can claim a tax credit for 30% of the cost of buying and installing a heat pump, up to $2,000! This includes any electric system upgrades needed to make the home heat-pump-ready. 20
These incentives aren’t limited to the federal level, as 15 states and 100 cities are offering low- and moderate-income households with point-of-sale rebates up to $8,000. And if your home needs upgrades in order to integrate a new heat pump? You might qualify for an additional $4,000 dollar rebate on those! 20
And it’s not just the United States. France, 21 Germany, 22 and almost 30 other countries already have heat pump rebates in place. As the war in Ukraine continues to increase gas prices around the world, more countries are considering similar forms of financial aid. 23 These rebates may not always cover the entire cost, but they make heat pumps viable for those who may not be able to afford one otherwise.
As a final added benefit, it’s estimated that by 2030 a surge in heat pump demand could require over 1.3 million workers to install all those pumps, nearly triple the current amount. 24 That’s potentially a lot of skilled, green jobs that we could add to the global economy.
Heat pumps are getting more popular every day, and it’s easy to see why. The issues that used to hold them back are dropping like the winter temperature as more innovators and home owners are investing in heat pump technology. If you’ve hesitated to get a heat pump in the past because you live in a cold climate, now’s the time to give heat pumps another look. There’s plenty of modern models on the market right now that can handle the coldest winters the Midwest or New England can throw at them.
As heat pump technology continues to improve at a rapid rate, complications like the disruptive installation process and sustainability concerns are actively being addressed. And with increasingly widespread government discounts from multiple sources, that high initial investment should be much easier to handle, so you and your family can just get around to enjoying the savings from the super efficient heat pumps.
It’s not often that we get an emerging piece of tech that actually makes serious strides toward decarbonization, saves you a significant amount of money, has very few drawbacks … and is already on the market. No matter your motivation to get one, whether that’s decarbonization or just saving money on energy costs, heat pumps aren’t just hot air.
- Heat Pumps Sustainability Workshop ↩︎
- Energy Star – How Does a Heat Pump Work? ↩︎
- COP and SPF For Heat Pumps Explained ↩︎
- Global Energy Crisis is Driving a Surge in Heat Pumps ↩︎
- Heat Pumps in 2023: what, how and why? ↩︎
- A Heat Pump Might Be Right for Your Home. Here’s Everything to Know ↩︎
- IEA Heating Fuels and Technologies ↩︎
- PV Magazine: The Economic Case for Heat Humps In Poland ↩︎
- Ground Source Heat Pump Installation ↩︎
- NEEP Heat Pump List ↩︎
- Variable Speed Refrigeration and Air Conditioning Compressors ↩︎
- Mitsubishi Inverter Heat Pump Technology Explained ↩︎
- Can Heat Pumps Actually Work in Cold Climates? ↩︎
- Do Heat Pumps Work In Cold Weather Climates? ↩︎
- DOE Residential Cold Climate Heat Pump Challenge ↩︎
- Lennox rises to cold climate heat pump challenge ↩︎
- Trane passes heat pump challenge ↩︎
- Air-source heat pump for harsh, cold climates ↩︎
- US manufacturer develops heat pump for cold climates ↩︎
- Clean Energy For All ↩︎
- Bloomberg: Heat Pump Incentives ↩︎
- Germany’s new rebate program for residential heat pumps has come into effect ↩︎
- IEA: The Future of Heat Pumps] ↩︎
- Heat Pumps On Fire Globally — As In, Getting Much More Popular ↩︎