Heating Buildings Leaves a Huge Carbon Footprint, But There’s a Fix For It

by |January 15, 2019

As winter weather sets in, the heat kicks on in New York City’s approximately one million buildings. Most of these buildings’ furnaces or boilers run on fossil fuels such as natural gas and oil; as a result, heating and hot water account for about 42 percent of the city’s total greenhouse gas emissions.

Vijay Modi, a professor in the Department of Mechanical Engineering at Columbia University and an Earth Institute faculty member, and his research group are studying how to decarbonize heating. His solution? Heat pumps that run on electricity—because as more and more electricity is sourced from renewable energy, “it is much easier and affordable to make electricity green than to make a green fuel.”

“Policy makers have recognized the value of heat pumps,“ he said, “And they are part of the New York State governor’s energy efficiency goals—that by 2030, we should have 25 percent of the heating from heat pumps.”

Electrified heating is important for the rest of the nation, too. To avert the catastrophic impacts of climate change, we must reduce our carbon emissions to zero as soon as possible. According to a 2018 report by the Rocky Mountain Institute,  reaching “deep decarbonization” goals of reducing greenhouse gas emissions 75 percent or more will entail, among other measures, eliminating most of the emissions produced by the burning of natural gas, oil or propane in American homes and businesses for heating and hot water.

What is a heat pump?

Modi describes heat pumps, which have been in use since the 1940s, as air conditioners with internal hardware and controls that enable them to operate in reverse.

A popular type of heat pump has an outdoor unit containing a compressor and condenser that works with an indoor unit (although heat pumps can also be contained in one unit). In hot weather, a heat pump operates like an air conditioner, pulling heat from air inside the home and transferring it outside, cooling the home.

In cool months, it pulls heat from the outside air and transfers it inside; counterintuitively, even when the weather is cold, the outside air contains enough heat to warm your home. While most heat pumps transfer heat from the air, there are geothermal and water source pumps that transfer heat from the ground or a nearby water source; others act as water heaters.

Heat pumps are more energy efficient than furnaces and boilers since instead of generating heat, they simply move heat from one place to another, and they can both heat and cool the home. They provide the most efficient heating and cooling available, producing two to four units of heat for each unit of energy used—a gas furnace produces a little less than one unit of heat per unit of energy.

Compared to furnaces and baseboard heating, heat pumps can reduce energy use by 50 percent. And according to a Natural Resources Defense Council (NRDC) study, over its lifetime, a new air-source heat pump can reduce greenhouse gas emissions by 46 to 54 percent compared to natural gas alternatives.

How to transition to heat pumps

Decarbonizing heating in New York City is challenging because of the city’s density, huge demand for energy, aging infrastructure, variety of building types, and space constraints. Modi’s Quadracci Sustainable Engineering Lab is researching how it might be done, studying the benefits of electrifying heating, and addressing potential issues that could arise.

When natural gas became cheaper than oil, many buildings in New York City converted from oil to gas. But since upfront costs to replace an existing natural gas system with an all heat pump solution are high, Modi doubts most people would opt to do this. Instead, to be cost-effective, retrofits could install heat pumps to be used the majority of the time, alongside existing heating systems.

He explained that buildings with a furnace that heats up air and distributes it could also incorporate a heat pump into its loop to heat the air. Little retrofitting would be required. A big high-rise building would present more of a challenge because it would require an industrial size heat pump, which would be difficult to retrofit.

Heat pumps might also more easily be adopted when buildings need to add or replace air conditioning or natural gas systems, upgrade their electrical systems, or do gut renovations. And new construction could easily rely entirely on electric heat pumps.

Concerns about heat pumps

There are concerns about what might happen if more and more electricity is needed for heating in the winter. System-wide electricity demand currently peaks in the summer with the use of air conditioning; Modi maintains we have the capacity to grow heat pump use until we reach a comparable winter peak. Getting there and beyond, wind resources could provide a solution. “We have very good off-shore wind resources right here in New York City,” said Modi. “It is a very good match for the heating, as we get stronger winds in the winter that would allow an increasing amount of heat to come from wind power.”

Heat pumps could replace air conditioners. Photo: Thomas Hawk

Another issue is that the electrical wiring of many buildings may not be able to accommodate the extra electricity needed by heat pumps, which run on 220/240 volts. Modi suggested that window unit air conditioners that run on 220/240 volts could be replaced by heat pumps (which also cool). “For most of your heating, when it’s above freezing, you may be fine,” he said. And in New York City, at least, “that may be what 60 percent of the heating need is. In addition you would be reducing emissions too.”

The outlook for the future

According to Forbes, “The global economy of the future is going to be driven by electricity and heated/cooled by electricity—not just powered by it.“

The Rocky Mountain Institute cited several factors that could help speed this transition and make heat pumps more cost-effective. As heat pumps catch on and manufacturers achieve economies of scale, prices will fall. Smart technology that can help shift the time of energy consumption could, for example, enable heat pumps to preheat a home in the early afternoon when electric rates might be lower and help integrate more renewable energy into the grid. Carbon pricing could entice more people to install heat pumps.

Even with our current electric grid in New York State, however, the electrification of heating reduces greenhouse gas emissions. And with a grid increasingly run on renewables, heating emissions could foreseeably be eliminated altogether.

“It may very well be that in the next 20 years, we will figure out how to make all electricity green and cheap all the time. Then we’d use heat pumps all the time,” said Modi. “But the pathway to doing that is tricky—as we make this transition, it has to be cost-effective.”

For new home construction, the NRDC study determined that in California, installing electric heat pumps instead of natural gas systems could save homeowners $1,500 upfront, and hundreds of dollars each year in operating costs. But since the initial costs to install or retrofit heat pumps may discourage some people from making the switch, utilities, governments, and manufacturers need to promote heat pump technology and make it more affordable. Financial incentives are key. “We are giving very big incentives to buy an electric car,” said Modi. “But dollar for dollar, it would be much better to do it for heating…because the emissions reduction would be very significant for the same amount of money.”

Some states are initiating programs to provide incentives for installing heat pumps, such as California, Maine, Massachusetts, Vermont, and others, including New York.


NYSERDA offers incentives to install heat pumps in multifamily and single family homes. Photo: Sagie

The Rocky Mountain Institute has made additional recommendations to utilities and policy makers to facilitate long-term electrification:

  • Make transitioning to heat pumps a priority in buildings that currently use propane and oil for heat and hot water, because they account for more than 20 percent of space and water heating emissions.
  • Stop installing natural gas systems in new construction since that infrastructure will eventually be obsolete as society decarbonizes.
  • To manage increased demand for electricity and existing electrified heating, create initiatives that include new rates, energy efficiency and that encourage consumers to move their energy use to off peak hours.
  • Update energy efficiency standards and goals to include emissions reductions across both electricity and gas so that utilities are not penalized for not reducing electricity demand.

Modi’s lab is examining how electrified heating would impact the whole energy system in the context of decarbonization. The researchers are studying electric vehicles, where they will be adopted, the installation of solar panels and home battery packs, how all this impacts the siting of wind, solar and transmission, and the overall implications for home owners and providers. Based on his research so far, he urged, “We should go full-steam ahead to install renewables and more off-shore wind in New York State. It’s expensive in the beginning, but as one installs more, those costs come down. Getting to 50 to 60 percent [emissions reduction], which is our short-term goal, is possible, is relatively affordable, and the technology for doing it is there.”

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ZnhM HAubreyRickkim Libera Recent comment authors
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Very interesting read! Those living in NYC, including myself, need to learn to lower our carbon footprint.

Kim Lee
Kim Lee

Great article. Its is so important that we keep educating ourself, and others, on how to use out resources most efficient, and lower our carbon footprint.

kim Libera
kim Libera

As an earth scientist/mathematician, I’m not one to warm up to the global alarmism perpetrated by Al Gore & all the fraudulent statistical methods. That being said in tackling the problem of micro-climates (topic in micrometeorology) the concept of the city heat island is a challenging one. I have seen only a handful of places tackle the issue with such things as solar roofs or parking lots, garden roofs, plants on the pilasters of bridge structures. This is all well in good because any vegetation absorbs co2. However, by the laws of thermodynamics we know that any energy production process… Read more »


It’s still electricity and making electricity pollutes. Heat pumps are very inefficient as soon as it gets below freezing they don’t work so good. Below zero not at all


Yes and in that case you can have a hybrid system which incorporates a thermostat that detects outdoor temperatures and at 34 degrees manages a heating method switch essentially which turns on the furnace to pull natural gas or propane. In Wisconsin, hybrid systems save a ton of money and energy because you use either/or depending on which is most efficient in the current conditions. And like New York, climate conditions can change drastically, sometimes multiple times in the same season. The only downside is expensive initial investment. After that, it’s great.


We tend to mix economics with energy efficiencies and carbon goals. Burning gas cannot meet carbon goals. Any functional heat pump is more efficient than burning gas. Problematically in southern Wisconsin my cost of electric is 7x more than gas (per equivalent btu). It is therefore economically more expensive to use electric despite having a well insulated house (ACH 1.0) with a hpwh. Half of my natural gas bill is line connect the other half is 97% furnace. There isn’t much more I can realistically do to reduce heat loss, economically what is needed is a carbon tax or preferably… Read more »


Geothermal heat pumps will operate in the coldest climates, the only problem is they need open space to install heart exchangers, or alternatively they need to be installed before building.