A real-world, data-driven analysis of the effect of indoor and outdoor temperatures on heat pump efficiency

Matt Traverso

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Published in

The New Climate.

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8 min read

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2 days ago

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Everyone understands that lowering the indoor temperature should save on heating bills, but did you know that the potential savings may be more than five times higher with a heat pump than with traditional equipment like a furnace, stove, or boiler?

Heat Pumps (HPs) are Air Conditioners that also heat. HPs generally have lower emissions and costs compared to traditional heating equipment like furnaces, stoves, and boilers (Figure 1), but they work best in mild weather.

The technology is fairly new and doesn’t behave the same as traditional home heating methods. I like to use the dawn of the microwave as an analogy: microwaves reheat food faster and easier than traditional methods but are terrible at making toast.

Just as early adopters had to learn the best applications for a microwave, we need to revisit the traditional heating maxims to optimize HP performance.

One common statement is that reducing indoor temperature by 1°F (0.6°C) reduces a home heating bill by 1%. This isn’t much. Most people would probably prefer a warmer temperature on a given day over a few extra pennies.

However, this general rule doesn’t apply to HPs because they are more sensitive to indoor temperatures than traditional heating equipment. This article demonstrates how lowering the thermostat can radically reduce HP costs and increase a HP’s functional range.

Disclaimer

Before I begin, I wanted to acknowledge that many commentators have nearly identical HPs that cool faster and in much lower outdoor temps than mine. Others indicate worse performance.

Home heating is a complex system that is influenced by home size, building material, ductwork, air handling, and insulation. For example, my HP seems to be limited by the diameter of my ducts vs. home size but upgrading would be onerous.