FAQ: How much more electricity will I use if I add a heat pump to my house?

If you are considering solar, the odds are good that you are also interested in being energy efficient in general. The most efficient way to heat a home is with a heat pump (aka “mini-split”), and the most efficient way to heat hot water is with a heat pump water heater.*

What exactly is a heat pump?

A heat pump is a mechanism that captures energy from one place, concentrates it, and delivers it as heat to another place. A window air-conditioner is a familiar type of heat pump, which captures energy from your indoor air and moves it to the outdoors. The result is a cooler indoor space and a (very slightly) warmer outdoors.

When people use the term “heat pump,” they are usually referring to a system that runs in the opposite direction: it captures energy from the outdoors and uses it to warm the indoors. “Cold-climate heat pumps” are versions specially designed to operate down to very low temperatures. Depending on the model, they can capture usable heat from the outdoors even when outdoor temperatures drop as low as -18°F.

Similarly, a heat pump water heater captures heat from the air in your basement and uses it to heat water for your shower and sinks.

The nature of the heat pump cycle means that heat pumps deliver useful heat far more efficiently than systems that generate new heat directly. This translates into energy savings and associated monetary savings.

If you start heating your home and/or water with heat pumps, this will reduce the amount of propane or heating oil you were using previously, while increasing the amount of electricity you are using. In almost all cases, what you spend on the electricity will be a good bit less than what you would be spending on fossil fuels. This is, of course, especially true if your electricity is generated with a PV Tracker.

So what will happen to your electrical usage if you go with heat pumps? According to Green Mountain Power, use of a cold climate heat pump of the following sizes will result in approximately the following change in electric usage and cost. Naturally, the exact electricity use will vary from home to home based on many factors.

Electric usage from a cold climate heat pump (Green Mountain Power)

Heat pump BTU ratingAvg. monthly bill increaseAvg. monthly kWh increaseAnnual bill increaseAnnual kWh increase
9,000$26163 kWh$3121,950 kWh
12,000$37231 kWh$4442,775 kWh
15,000$47294 kWh$5643,525 kWh
18,000$63394 kWh$7564,725 kWh

Source: Green Mountain Power presentation at Montshire Museum of Science, June 7, 2016.

As for a heat pump water heater, here’s what that looks like.

Electric usage from a heat pump water heater

# peopleGallons used per dayAverage electricity usage to heat waterCost @ GMP residential rates
119.5716 kWh/yr60 kWh/month$10 per month
235.81,315 kWh/yr110 kWh/month$18 per month
352.01,910 kWh/yr159 kWh/month$26 per month
468.22,505 kWh/yr209 kWh/month$34 per month
584.43,101 kWh/yr258 kWh/month$42 per month

Sources: Parker & Fairey, “Estimating Daily Domestic Hot-Water Use in North American Homes” ; 10 CFR 430, Table III.3 Medium-Usage Draw Patterns ; calculations based on energy guide label.

* True, a solar hot water system can be even more energy efficient, but I defer to Martin Holladay at Green Building Advisors that “solar thermal is dead.”

See more FAQs here, or quickly jump to electric use by household appliances or electric vehicles.

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