Heat pumps could be key to fighting climate change, but how? We answer your burning questions.

Instead of converting 100,000 homes a year, as its climate plan dictates, Massachusetts last year switched just 461 households from fossil fuels to heat pumps.Ryan Huddle

Massachusetts has sworn to get 1 million homes and other buildings off fossil fuel by the end of the decade, a target made even more urgent by recent revelations that the climate is in worse condition than previously thought. But, as we reported earlier this week, the state is way behind.

Instead of converting 100,000 a year, as its climate plan dictates, last year just 461 households switched from fossil fuels to heat pumps.

There are a lot of reasons why heat pumps have been slow to take off in the state, including high costs, lack of confidence by consumers, ignorance of the technology among many heating contractors, and a failure by the state’s energy efficiency program, Mass Save, to embrace full home electrification.

As our inboxes will attest — you, the readers, have questions. Lots of them. Here are the ones we heard the most frequently.

How does a heat pump work?

Heat pumps are devices run by electricity that can move thermal energy from a cooler space to a warmer one. Even when it’s cold outside, air contains energy. The heat pump sucks that energy in and uses it to warm a chilly house in the winter, or cool it in the summer.

One easy way to think of it is to imagine a highly efficient and quiet air conditioner that can work in both directions.

There are a few different kinds of heat pumps, including air source heat pumps that move energy from a device outside a building to one that’s inside, or a ground-source (or geothermal) heat pump, which draws energy from the soil or groundwater and pulls it into a building.

But one thing is clear: These are not the same thing as the inefficient electrical resistance heaters of the mid-1900s.

If we switch to electrifying our homes, but the grid is still powered by oil and gas-fired power plants, won’t we still be contributing to emissions?

Yes, but less than you otherwise would.

On the one hand, heat pumps are super efficient, which means your overall energy demands will be lower.

On the other, as long as electricity is still being generated by fossil fuel-fired power plants, we’ve still got a major emissions problem on our hands. That’s why shifting buildings and vehicles to electricity is only part of the massive undertaking the state is working on as it strives for net-zero carbon emissions by 2050.

Renewable energy currently makes up about a quarter of the state’s total electricity generation, according to the Energy Information Administration, largely driven by small-scale solar panel systems.

The climate legislation passed earlier this year requires that utilities procure an additional 2,400 megawatts of wind power, bringing the total planned state procurement to 5,600 megawatts. For reference, the Vineyard Wind project will have an 800 megawatt capacity — enough to power more than 400,000 homes. Construction is expected to start later this year.

At the same time, the state is working toward ambitious expansions of solar and hydro power.

How much will the electrical grid need to expand for a shift from fossil fuels to electricity for cars and buildings?

To put it briefly — a lot. A study by the economic and regulatory research company The Brattle Group found that by 2050, as people switch to electricity for heating and cooling and for their vehicles, electricity demand could well be twice the current level. That analysis was based on an earlier goal of 80 percent emissions reductions by 2050, rather than the current goal of net-zero emissions.

And it’s not just the electricity demand that will need to grow. So, too, will the transmission system. A 2020 study by Princeton University found that across the country, in order to meet the increased electricity demands that come from meeting a net-zero emission goal, the grid will have to expand its transmission system by 60 percent by 2030, and may need to triple it by 2050.

The $1 trillion national infrastructure bill that was passed earlier this month by the US Senate includes $73 billion to modernize the electricity grid nationwide.

If people are hesitant to fully convert to electricity now, are they still helping the climate by installing a heat pump but keeping a backup system?

Yes. According to Harvey Michaels, a lecturer in Energy Management Innovation at MIT and a research director of Energy Management Practice and Innovation, homeowners who install a heat pump but still use a backup system will reduce their on-site carbon emissions for heat by 50 percent to 80 percent.

And for various reasons — whether it is concerns about a heat pump’s ability to adequately warm a home, or the high costs of installing heat pumps — sometimes people prefer to start small as they make the switch. After dipping their toes in, experts say they expect more homeowners to eventually get rid of their backup systems entirely.

There is a downside, though. As Jeremy Koo, an associate at the technical and strategic consulting company Cadmus told us, keeping fossil fuel equipment in your house can cut down on your ability to cut emissions and also “has implications for the infrastructure that’s in place to continue supporting fossil fuel delivery.”

I’d like to get a heat pump — what’s the first step I should take?

According to the experts at the Northeast Energy Efficiency Partnerships (NEEP) and Mass Save — the state’s utility-run energy efficiency program — a free energy assessment from Mass Save is a great first step. They will send an auditor to help highlight changes you can make to your home to help it run more efficiently, which may include sealing up drafty leaks and adding insulation — both things that can help cut down on heating and cooling costs.

Another thing to keep in mind is your home’s electrical panel. If you might want to get heat pumps now, and an electrical vehicle five or 10 years down the line, planning for that added demand now can save you from having to do pricey electrical work multiple times.

You can find more helpful advice in this story by the Globe’s Janelle Nanos:

Where can I find contractors who can help?

The Massachusetts Clean Energy Center has a list of air-source heat pump installers that could be a good starting point.

You can also take a look at NEEP’s air-source heat pump buying guide for advice, and a checklist of important questions to ask a contractor. “If your contractor says ‘heat pumps don’t really work in cold climates’ or ‘every heat pump needs a backup system,’ find someone else,” the guide says. “Remember, the lowest bid isn’t always the best value, and a high price doesn’t guarantee competence or quality.”