Energy
Heat pumps and the electrification of heating
A technology that delivers several units of heat per unit of electricity, and a set of practical obstacles that have very little to do with the physics.
Space and water heating account for a large share of energy use in cold and temperate countries. Heat pumps are the main route to decarbonising it, and the arithmetic is genuinely favourable.
Why they beat combustion
A gas boiler converts chemical energy to heat with efficiency approaching but never exceeding one hundred percent.
A heat pump does not create heat. It moves heat from outside to inside using a refrigeration cycle, and the electricity powers the movement rather than supplying the energy.
Which means it can deliver more heat energy than the electrical energy it consumes. The ratio, the coefficient of performance, is typically between two and four depending on conditions.
Delivering three units of heat per unit of electricity is not a violation of anything. It is what a refrigerator does, run in the other direction.
Why efficiency falls in cold weather
The COP depends on the temperature difference the pump works across.
Extracting heat from air at ten degrees and delivering it at thirty-five is easy. Extracting from minus ten and delivering at fifty-five is much harder.
Which produces the two design rules that determine whether an installation performs well.
Lower flow temperature is better. A system designed to run at thirty-five to forty-five degrees is dramatically more efficient than one running at seventy, which is what many older radiator systems were sized for.
This is why heat pump retrofits frequently involve larger radiators or underfloor heating: not because the pump cannot produce heat, but because low-temperature emitters let it produce heat efficiently.
Cold climate performance has improved substantially. Modern units using variable-speed compressors and enhanced vapour injection maintain useful output well below freezing, and field data from cold regions confirms it.
The older claim that heat pumps do not work in cold climates is out of date, and it persists partly because early installations were genuinely poor.
The types
Air source. Extracts heat from outside air. Cheapest to install, most common, efficiency varies with outdoor temperature.
Ground source. Extracts from the ground via buried loops or boreholes, where temperature is stable year-round.
Higher and more consistent efficiency, substantially higher installation cost because of the groundworks.
Water source, using a river, lake or aquifer where available.
Air-to-air, which delivers heat as warm air rather than to a water system — effectively a reversible air conditioner, and the dominant form in several countries.
That last point is worth noting: in much of the world heat pumps are already ubiquitous and are simply called air conditioning.
What actually goes wrong
Almost never the technology.
Poor design. Undersized emitters, incorrect heat loss calculations, and systems set to run at high flow temperatures because that is how the installer has always done it.
Oversizing. A unit larger than the load cycles on and off, which reduces efficiency and shortens compressor life. Correct sizing requires a proper heat loss survey, which is skipped more often than it should be.
Controls. Heat pumps work best running continuously at low output, modulating to match demand — the opposite of a boiler's intermittent bursts.
Users who set them to switch on and off in blocks, as they did with a boiler, get poor efficiency and conclude the technology is at fault.
Installer skill. The binding constraint in most markets. Training and certification have not kept pace with demand.
The economics
Determined mainly by the ratio of electricity price to gas price.
A heat pump delivering three units of heat per unit of electricity beats a gas boiler on running cost only if electricity costs less than roughly three times the gas price per unit of energy.
In several markets, electricity carries policy levies that gas does not, which pushes the ratio unfavourably and undermines the case despite the physics being sound.
Rebalancing those levies is the single largest policy lever available, and it costs nothing to build.
Installation cost is the other half, and it is substantially higher than a boiler replacement — which is why subsidy programmes exist and why their design matters.
The grid consequence
Widespread electrification of heating shifts the annual peak in cold countries from summer cooling to winter heating, and raises it.
Heat demand is weather-correlated and coincident across a whole region, which is exactly the hardest kind of load to serve.
Which is why thermal storage — hot water tanks, or building fabric used as a heat store — matters more here than elsewhere. Shifting heating demand by a few hours is cheap and substantially reduces peak requirements.
Insulation does the same job by reducing demand outright, and remains the cheapest intervention available in most housing stock.
