Alexis Abramson’s first love was the study of heat—how to use it, conserve it and eliminate waste.

“Everyone connects with heat in some way,” says Abramson, dean of Columbia University’s Climate School. “Yet heat is sort of the black sheep of the energy family.” We need heat for obvious reasons, and yet when we use other forms of energy like electricity, we often want to minimize waste—which means we don’t want it converting to heat unnecessarily.

In addition to serving as the Climate School dean, Abramson is also an energy efficiency expert, specializing in building upgrades and retrofits. Under the Obama Administration, Abramson was the chief scientist in the Buildings Technologies Office, and so experienced firsthand all aspects of the research, development and deployment around energy-efficient buildings.

Before coming to Columbia, Abramson was the dean of engineering at Dartmouth College, and prior to that an engineering professor at Case Western Reserve University, where she also led their energy institute. In the following Q&A, Abramson discusses how she first became interested in energy efficiency, how heat pumps work, and how homeowners can take some simple steps to minimize their carbon footprint and energy bills. (Click here for an animated primer on energy efficiency at home.)

What piqued your interest in energy efficiency?

I always really loved the clarity and logic of math and science. I decided to study mechanical engineering as an undergraduate, and I really connected with the concept of heat. We learned the underlying science about heat transfer and thermodynamics, two subjects I grew to love. Everybody needs heat, right? We’re always adjusting our environment to stay comfortable, whether heating or cooling our homes, or preparing meals.  

That put me on a path toward conducting research on heat, manipulating thermal properties and materials and trying to see if we could use waste heat and convert it back into electricity—an area called thermoelectrics. After several years of slow progress, I decided I wanted to focus on more practical applications, and that took me into buildings and building efficiency—something we still struggle with tremendously.

Can you talk a little bit about energy and buildings? Why is retrofitting buildings so important?

There arethree major reasons to make buildings cleaner and greener: to save money, to contribute to the reduction of emissions, and for resilience. Residential solar, for example, provides clean electricity directly to your home. If your power goes out, so long as your solar system is set up properly, then you have access to electricity when maybe your neighbors don’t.

There is also a push to electrify everything in buildings, so that once the grid is 100% green, or close to it, everything we’re running in our house by electricity is green and clean. You wouldn’t even need solar panels on your roof at that point, if your goal is to minimize carbon, because you would be able to get 100% of green electricity from the grid.

I think it’s important to think about how we want to prepare our homes for the future and for a greener, cleaner world.

Let’s pivot to some steps homeowners can take to reduce carbon emissions. Solar seems to be atop the list.

Solar panels are worth the investment in virtually all parts of the U.S. If I can pay up front to put solar on my roof, that electricity is essentially free to me, and the payback time is less than 12 years for most homes. And solar panels usually last 20 to 25 years, so for eight or more years, the electricity really is free. The issue is oftentimes the rather large upfront capital costs, but in many parts of the country, there is green financing or clean energy programs available so more people can access the technology.

Another topic that crops up a lot when talking about energy efficiency: heat pumps. What are they and how do they work?

Heat pumps are my favorite topic. “Heat pump” is sort of a general category for heating and cooling and, as it sounds, a heat pump moves heat from one place to another. Your air conditioning system is a heat pump, and so is your refrigerator. What your refrigerator is doing, essentially, is taking the heat from the inside and pushing it out the back of the refrigerator into your kitchen. Same thing with an air conditioner—that’s why you need an outside unit, because you need to move heat from inside the house to the outside.

Heat pumps run on refrigerants. These refrigerants absorb and release heat as they cycle through different pressures and temperatures. For example, if 30-degree Fahrenheit air flows over a refrigerant that’s 10 degrees F, the refrigerant absorbs that heat. It’s a clever application of thermodynamics.

Can they work in really cold climates?

Absolutely. Even at -10 degrees F, you can design a system with refrigerants that operate below that temperature to extract heat. It’s a little more complicated, but manufacturers are making major improvements with cold-climate heat pumps. There are different setups—central ducted systems or ductless mini-splits, which are common in Europe. I have mini-splits in my own home. They allow for zoned heating and cooling and connect to a single outdoor condenser unit.

How about the reverse? If you want to cool your home instead of warm it?

It’s the same principle. You can take heat pumps used for cooling and run them essentially the opposite way and use them for heating. You take the heat from the cold outside air and push it to the inside of your house. For example, if your indoor air is 80 degrees F and the refrigerant is 50 degrees F, that refrigerant absorbs the heat and expels it outside. You’re just reversing the flow of heat.

What about hydropower—can individuals use that?

Hydropower makes the most sense if you live in a rural area and near a river that’s constantly running. Otherwise, it’s generally not cost-effective for homes. But at the utility scale, it plays a big role—think of massive projects like Hydro-Québec.

What’s a cost-effective improvement every homeowner should consider?

Insulation. Most homes in the U.S. are poorly insulated. People often upgrade their HVAC systems without realizing a well-insulated home needs less heating and cooling power in the first place.

Better insulating your house can be relatively simple or very complex. But something as simple as going to a hardware store, getting some pink insulation and rolling it out into attics and crawl spaces can make a big difference.

The biggest cost of energy in most parts of the country is heating—not cooling, contrary to popular belief. Most of the heat escapes through the roof of your house. Stopping that heat loss is one way to cut your energy bills.

How much money can you save by implementing these changes?

Some basic changes can really save you money. Studies have shown around 30% on average on your energy bills, though it’s highly variable. Some homes might save as little as 10%, others as much as 70%. In the winter, those saving can be substantial.

But some upgrades are quite expensive.

Yes, the upfront costs of installing solar panels, heat pumps or new windows can be quite high. But many states and localities have rebate programs or green financing programs. Utilities often have green financing programs too. For example, they might pay the upfront cost of a heat pump and let you repay it over time through your utility bill—kind of like a car loan.

New York City, for instance, offers rebates for switching to induction stoves. And power purchase agreements (PPAs) for solar let homeowners pay nothing upfront and lock in lower electricity rates. And then after 12 years or so, homeowners own the solar panels and then electricity is free.

And then there’s the Inflation Reduction Act, passed during the Biden administration. While some elements are being rolled back, it still offers lots of rebates and tax credits for energy-efficient home improvements. It’s especially geared toward lower-income households, helping ensure equitable access to clean energy technologies.