How will we keep warm in the winter?

Heating is probably the harder half of the comfort problem across most of the rich north, for two reasons that compound. It uses several times the energy cooling does, and the large majority of that energy comes from burning something on site, whereas cooling is already electric and so gets cleaner automatically as the grid does. The fix is therefore to do more heating the way we already do cooling, with a heat pump, which moves heat instead of making it and so delivers several times more heat energy than the electricity it consumes. Physics does not object to running the cycle backwards: there is plenty of heat in the air on a cold night, since our sense of cold is biology rather than thermodynamics.

Most of the post is about why we mostly do not, and the weighting matters more than the list. Up-front cost is real, but he concludes it is not the primary constraint for most buildings, because a heat pump bought for heat also delivers air conditioning, which more owners want or must replace anyway. It binds hard in particular categories: cold-climate homes with old pipe-and-radiator distribution, and tall city buildings that may have nowhere to put outdoor units and no ducts big enough for peak heat. He gives more weight to the softer barriers, that buying and installing the things is a mess, that contractors in his area often talk customers out of them, and that most heating systems are bought in a panic when the old one dies, when the cheapest thing that can be fitted before the pipes freeze always wins.

Two of the three barriers he labels hard are physical. A heat pump works harder the larger the lift, so its efficiency is worst exactly when heating demand is highest. In North America, where gas is cheap against electricity, that means the efficiency needed to beat a gas furnace on running cost in cold states is higher than the best equipment is rated to reach, which is why heat pumps are winning in the humid Southeast and in sun belt new-build while stalling north of the Mason-Dixon line. The same curve creates the peak problem, which he treats as the hardest of all: heat pumps cut total heating-season energy substantially but cut the winter peak far less, so at scale they could become the dominant driver of peak demand, straining everything from generating capacity to service transformers. What that costs is the part he says nobody really knows.

The third is the working fluid. The refrigerants that make the cycle work are potent greenhouse gases, they leak across a machine’s life, their phase-out is already agreed internationally, and unlike the last substitution there is no obvious drop-in successor, so a heat pump’s emissions are not purely a function of grid carbon. He defends them anyway, because nothing else scales: capture at building scale founders on moving CO2 out of billions of buildings, hydrogen can only be blended into gas networks in small proportions without extraordinary policy coordination, and renewable gas, which he expects to beat hydrogen but only in a supporting role, is capped by how many landfills, cows and pigs there are. Hence heat pumps, plural. Ground-source systems trade heat with the earth instead of the outdoor air, which shrinks the lift, makes them efficient year-round and largely removes the winter peak, at the price of digging or drilling. Thermal heat pumps run the same cycle on burning fuel rather than a motor, which keeps the cheaper energy source, works in deeper cold, leaves the grid untouched and can use a refrigerant with no warming potential, at the price of still burning gas. His closing position is that a partial answer available now beats a pure one later.