May 14, 2025 11:00:31 AM

HVAC Building Science Today's Homeowner The Evolution of Green Building 20th Anniversary

Is It Ever “Too Hot” for Heat Pumps?

Matt Power, Editor-In-Chief

2 min read

Is It Ever “Too Hot” for Heat Pumps?

3:34

Extreme temperatures put home cooling to the test, but don’t assume that heat pumps can’t hold their own.

I heard a project manager at a meeting in Las Vegas recently say the reason the company doesn’t install heat pumps is because the Vegas climate is just too hot. I had never heard this particular objection to the technology.

So, I started digging around.

After a lot of time reviewing various engineering articles and reports on heat pump performance, I found one of the best side-by-side research pieces on the topic by the Rocky Mountain Institute. In it, engineers compared the performance of three of the most common types of home HVAC systems:

“RMI modeled the performance of several cooling options for a Seattle home during the three-day heat wave in June 2021: an air-source heat pump (hereafter heat pump), a typical AC unit and a higher capacity AC unit.”

What they found was that not only were heat pumps able to handle high outdoor temperatures, they did so without allowing the house to fluctuate uncomfortable above the set point—all while using less energy than other technologies.

These three graphics summarize their findings nicely:

Too Little Too Late. When modeled with a typical 2-ton AC system, the home’s interior temperatures soared well above the set point. Energy consumption was less than the other equipment, but this system was insufficient to meet the extreme heat challenge.

Better, But Power Hungry. A more powerful 4-ton AC unit used twice the energy as the 2-ton unit but still struggled to keep the house comfortable as outdoor temperatures hit 108 degrees Fahrenheit.

Cool and Steady. The researchers also modeled a variable speed SEER 22 heat pump without the gas furnace. They found it was best able to maintain indoor set point, and used 18.6 percent, 15.5 percent, and 3.7 percent less energy than the high-capacity AC unit for June 26-28. The difference in energy use for each day can be attributed to the rising outdoor temperature. Outdoor, temps were recorded at 102°F, 104°F and 108°F degrees, rising each day over the study period.

Unlivable Interior? One of the more shocking revelations to come from this research is what happens to a home without any form of cooling. By the end of the third day, the modeled home had hit 100.4°F inside, only a few degrees below the outdoor, scorching environment.

This suggests that more research (and resilience) is needed, to prepare modern homes for the future shocks of longer periods of extreme heat. For example, we should all be looking harder at radiant barriers, cool roofing, masonry effect, natural ventilation, and other strategies for mitigating heat. Power outages are on the rise, and heat pumps are currently the strongest mechanical comfort machines, but the less we can rely on them to deal with climate extremes on their own, the better our long term resilience.

If you’re not clear about how heat pumps work, this article goes into great detail to explain the intricacies of how heat pumps work, most notably discussing the concept of “lift” (the difference between desired and ambient temperatures) and how the low pressure/high pressure balance works conceptually.

infinity-24-heat-pump-with-greenspeed-intelligence-25VNA4

Products such as this Carrier Infinity 24 25VNA4 Heat Pump not only can handle high heat, they do so more smoothly and efficiently than other options. Image credit: Carrier

Publisher’s Note: Green Builder's 20th Anniversary celebration is sponsored by: Carrier, Trex, and Mohawk.

May 14, 2025 11:00:31 AM · 2 min read

By Matt Power, Editor-In-Chief

Veteran journalist Matt Power has reported on innovation and sustainability in housing for nearly three decades. An award-winning writer, editor, and filmmaker, he has a long history of asking hard questions and adding depth and context as he unfolds complex issues.

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