The whole truth

Heat pumps aren’t great in the cold.

In politics, flipping half-truths like flapjacks is part of the job description. Self-preservation is the name of the game and such is reflected in the rhetoric we see from politicians today.

For example, let’s say a presidential administration touts “the lowest inflation in decades” on the re-election campaign trail. While this might be factually accurate, what if the inflation figure was for the past year alone? The administration can claim success, despite the reality that inflation over the past four years set a record.

At the other end of the corporate-government complex, industry is guilty of similar tactics. Company executives often bend over backwards to paint an overly rosy picture of their financial health. They might attribute 20% YoY revenue growth to robust market demand, strategic innovations, and other corporate jargon. However, the whole truth might be that there was a one-time accounting adjustment that artificially inflated revenue figures. Without this context, investors are led to believe that the company's core operations are far more successful than they actually are. Executives didn’t leave that information out, but they weren’t particularly forthcoming with it either.

These generalized examples illustrate how half-truths can be wielded to create misleading narratives. By presenting selective pieces of information, companies and politicians can craft messages that obscure reality.

Unfortunately, politicians and companies consistently spew half-truths on energy. This can only go so far because the energy business is the ultimate reality business. The media should, theoretically, help us wade through the never-ending stream of BS. However, the mainstream media repeats half-truths without thinking like Ron Burgundy reads a teleprompter.

Damn it! Who typed a question mark on the teleprompter?

When you tell the public half-truths, is it any wonder that people are turning to alternative channels for more thoughtful information?

Welcome to an alternative channel to learn the whole truth about residential heat pumps!!

While heat pumps are improving and already incredibly useful, they’re far from perfect. But when one looks at them with carbon blinders, every downside is minimized into oblivion. My intention here isn’t to bash a useful technology, it’s to answer the question of the day in heat pump land — “do they work in the cold?”

When compared to residential heating alternatives, the key distinction with heat pumps is that they transfer heat rather than create it. Furnaces and boilers create heat by burning fuel (propane, natural gas, or oil), heat pumps use electricity to transfer heat via a refrigeration cycle. You can pretty much anticipate all of the pros/cons of heat pumps by understanding this basic operating distinction.

The efficiency of a heat pump is expressed as a coefficient of performance (COP). The COP of many heat pumps is in the 3-4 range, meaning that for every 1 kW of electricity input, you output 3-4 kW of heat equivalent. Because of this, heat pumps have developed a reputation for being tremendously efficient. Rightfully so, it’s pretty nuts that you can get 4 kW of heat output from 1 kW of electricity input. Engineering is cool.

Since burning natural gas for heat has a ~90-95% efficiency, you’ll typically hear that heat pumps are 3x more efficient than fossil-fueled furnaces.

However, comparing these two efficiencies is an apples-to-oranges comparison. As any good engineer knows, deciding where to draw boundaries is critically important in determining the efficiency of a system. If we compare the efficiency of burning natural gas in a furnace to that of burning it in a power plant to create electricity for a heat pump, the calculus changes. After considering transmission & distribution line losses, the conversion efficiency of a combined-cycle gas power plant is about 50%. That means that every 1 unit of natural gas used in the power plant will create 1.5-2 units of heat. Still 1.5-2x more efficient than a furnace, but less so than typically advertised.

Since the vast majority of residential heat pumps transfer heat from ambient air outside the home (instead of the ground), it stands to reason that their effectiveness decreases as the outside temperature decreases. It’s still possible to transfer heat into a home when it’s freezing outside, but it’s not as easy compared to when it’s 50°F.

The figure below gives you a sense of how capacity and efficiency (COP) change for an air source heat pump (ASHP) at different temperatures. The heating requirement (BTU/hr) and ASHP capacity lines intersect at the “balance point” where the heat pump can no longer keep up with demand.

Source

The typical balance point where a cold climate heat pump can meet heating demand without additional heat sources is often cited around 25°F.

What’s the most common supplemental heat? Electric resistance heat.

As temperatures approach 15°F or lower, the 3-4 COP mentioned previously will be reduced by ~50% to 1.5-2. At the same time, electric resistance supplemental heat will come on with a COP of 1.0. So if a house uses a heat pump for heating, electricity demand will skyrocket as temperatures plummet. If heat pumps are deployed in mass and you don’t have a grid that can handle this, you risk inducing very dangerous blackouts. So you best be careful if you’re a cold climate like New England mandating renewable generation on the grid while simultaneously spending $450mm on heat pump deployment.

Even though performance drops in the cold, you might hear heat pump peddlers say “deniers will tell you that heat pumps don’t work in the cold, but some of the coldest countries in Europe have the highest rate of adoption.”

Yes, Norway, Sweden, and Finland have some of the highest rates of heat pump adoption. However, these Nordic countries benefit from substantial hydropower that keeps their electricity costs low. The lower fuel cost lessens the pain of the lower performance. Additionally, home sizes tend to be half the size of our bigger-is-better American homes.

Lastly, let’s talk about the experience aspect of heat pumps. Capacity and COP are cool and all, but what does it feel like?

People typically perceive the quality of heat from heat pumps as less consistent and less warm compared to natural gas furnaces. Heat pumps provide a milder, more gradual heat that can be less satisfying in colder climates. They also blow air at lower temperatures than natural gas furnaces, which can deliver a quick, intense burst of heat, making spaces feel warmer faster. You can use a heat pump in the cold, just like you can take a road trip with an EV. However, just because you can doesn’t make it a great experience.

I asked

Robert Bryce

about his opinion on heat pumps and I’ll let his response take the point home:

I believe my exact line was “heat pumps suck.” I stand by that statement. I have direct experience. I have lived in a house with a heat pump and have one in my backyard office here in Austin. The issues:

1. They don’t work well in very cold weather. This is a well-known problem. I use a heat dish for heat because it is more effective.

2. The heat pump machinery is noisy. At least the ones that I have used for full-house units were. Some of the smaller condenser units aren’t as loud but I’m averse to noise.

3. The quality of the heat just isn’t as pleasing as forced-air gas or radiant heat from a hot water system.

Next time you hear how great heat pumps are in the cold, now you know the whole truth.

Heat pumps are most effective in temperate climates with access to cheap and reliable electricity. They work almost everywhere, but they’re not great everywhere. You’re smart enough to figure out if it would work for your personal situation.

Heat pumps will continue to improve and I’m all for them, but is a little realism too much of an ask?

Thanks for reading! Your feedback is always welcomed!