H eat pumps , a type of reverse-refrigerator used for warming homes, are not the type of tech that gets most investors hot and bothered. They were, after all, invented in 1856. Harald Mix and Carl-Erik Lagercrantz, two Swedish financiers, see things differently.

The pair, whose investment group Vargas is behind Northvolt, a battery maker, and H 2 Green Steel, which uses green hydrogen to produce steel, sense there are big bucks in replacing Europe’s many oil and gas boilers with heat pumps. Earlier this year Aira, a company founded by Vargas, launched a new product that it hopes will entice more people to make the switch. It is not only profits that are at stake.