Heating things up accounts for the single largest share of our energy consumption and greenhouse gas emissions.

By things, we mean a whole laundry list of key ingredients in our lives, including (but not limited to) actual laundry:

It warms and cools our homes.

It cooks our food.

It cleans and dries our clothes, both at home and at the dry cleaners.

But heat goes far beyond our daily routines.

Heat is at the core of so many things most of us probably don’t think of but that we all rely on like cement, steel, glass, greenhouse heating and chemicals.

Oil, natural gas and coal provide nearly 90% of the heat consumed in a range of sectors worldwide, including electricity, buildings and manufacturing, according to the International Energy Agency. This accounts for roughly half of the world’s energy consumption and 40% of global carbon emissions (see below for chart ).

These numbers don’t get the attention that, say, transportation or electricity does, because heat’s impact is spread out across most sectors of the economy—but it should.

When we talk about heat, we mean anywhere from 20 degrees Celsius—68 in Fahrenheit—that we humble laypeople are most familiar with when heating our homes, to thousands of degrees Celsius, the toasty temperature needed to make things like cement and glass.

Source: The Energy Progress Report 2021• Report by the International Energy Agency and several other intergovernmental groups.

The big picture of the energy transition is clear: The world must electrify as much of the economy as possible, including cars and buildings.

The center of that electrification will, in turn, likely be wind and solar energy, which are rapidly becoming the cheapest electricity options around the world.

But stubborn and expensive exceptions exist to that paradigm—and many of them are hot.

Let’s look at two big exceptions: 1) the potential of and limits to electrifying building heating, ventilation and cooling systems and 2) the massive amounts of extremely high heat needed for industrial manufacturing processes.

Electricity-powered heat pumps are getting more attention these days as a sustainable way to transition away from direct natural gas heating.

In Europe, heat pumps are considered a key way the Continent can kick its Russian natural gas habit, much of which goes to heating homes and other buildings.

Despite their one-sided names, heat pumps are two-in-one devices that both heat and cool buildings.

They are becoming an increasingly ideal solution for new buildings with prices dropping and subsidies growing.

In the U.S., for example, heat pump sales for new single-family homes top 40%, and sales are nearly 50% for new multi-family buildings, according to the IEA.

But using electricity to heat new buildings is missing the main problem.

Roughly 80% of the predicted buildings needed for 2050 have already been built, according to consultancy McKinsey.

Retrofitting existing buildings, including replacing fossil fuel boilers with heat pumps, is one of the biggest challenges of the clean energy transition, per an IEA expert.

“Many countries face substantial upfront costs when it comes to energy retrofitting of buildings, as well as lack of information and skills to perform retrofits in effective and cost-effective ways,” said Ksenia Petrichenko, an energy efficiency analyst at the IEA. “Most buildings built several decades ago are not up to the standards we need right now to comply with our net-zero goals.”

Buildings account for 47% of heating demand, largely for space and water heating, according to the IEA.

The biggest end-use demand for heat—50%—comes from industrial processes, that is, the making of all of life’s mundane but essential foundations: cement, steel and more.

At a certain point (or, more accurately, by a certain temperature), electricity can’t cut it from a pure physics perspective.

“The higher temperature you go, the harder it is to decarbonize,” said Tony Pan, co-founder and CEO of Modern Electron, a startup whose technology turns wasted energy from home natural gas furnaces and hot water tanks into electricity.

Source: Rhodium Group analysis of U.S. Energy Information Administration data.

Oil, natural gas and coal continue to dominate heat generation for understandable reasons: They’re good at their stated purposes from a physics perspective—and they’re affordable.

“If I’m doing anything that needs temperatures of 1,500 to 2,000 [degrees] Celsius—like steel and glass—it’s really, really hard to try to find anything that’s even close to cost competitive to natural gas,” said Eric Toone, co-leader of the investment team for Breakthrough Energy Ventures. “How else am I going to generate that heat, especially that quality of heat?”

To more cleanly heat buildings, solutions include repurposing existing infrastructure and more aggressively incentivizing heat pumps.

To more cleanly use heat in industrial manufacturing, numerous startups are trying to crack that code. Keep reading for a glimpse.

Editor’s note: Breakthrough Energy Ventures is affiliated with the broader Breakthrough Energy network, which supports Cipher.