Heating by moving heat

Materials, refrigerant, electricity, insulation, climate and service life.

It does not manufacture heat: it moves it

The cycle that makes delivering more than it consumes possible

A heat pump compresses and expands a refrigerant fluid in a closed circuit, taking advantage of the fact that this refrigerant changes state — from liquid to gas and back to liquid — at different temperatures depending on the pressure it is subjected to. In the evaporator, the low-pressure refrigerant boils at a temperature lower than that of the outdoor air, ground or water, absorbing heat from that environment even if it is cold in absolute terms — air at zero degrees still contains plenty of usable thermal energy. The compressor then raises that gas's pressure and temperature, and in the condenser the now-hot refrigerant releases that heat indoors and condenses back into a liquid. An expansion valve reduces its pressure again and the cycle repeats. In summer cooling mode, a reversing valve flips the entire direction of the cycle, and the same unit extracts heat from indoors and expels it outdoors.

Why it can deliver more energy than it consumes

The compressor is the only part of the cycle that needs electricity; its job is to compress the refrigerant, not to create the heat that ends up being delivered. That heat comes mostly from the outdoor environment it was extracted from. That is why a heat pump's so-called coefficient of performance (COP) — the ratio between useful heat delivered and electricity consumed — can be substantially greater than one, something no electric-resistance heater can ever achieve, because that heater does convert all its electricity directly into heat, without extracting anything additional from the environment. Real-world performance varies with the temperature difference the unit has to bridge: the smaller the gap between the outdoor temperature and the flow temperature the indoor heating system demands, the higher the performance achieved, and vice versa.

Manufacturing it also carries a physical and environmental cost

Building a heat pump requires steel and copper for the compressor and heat exchangers, aluminum for the coil fins, electronic control components, structural plastics, and a refrigerant charge that must be manufactured, transported and, at the end of the unit's service life, properly recovered. Some refrigerants historically used in this type of equipment have a very high global warming potential if they escape into the atmosphere through a leak or poor handling when the unit is decommissioned, so choosing lower-impact refrigerants, installing the unit correctly to minimize leak risk, servicing it periodically, and recovering the refrigerant at end of life are decisions that matter as much as the cycle's own energy efficiency. The outdoor unit also generates audible noise and needs clear physical space; a geothermal installation that draws heat from the subsoil, more efficient in many climates, adds the further cost of drilling wells or digging trenches.

The building and the heat-distribution system matter as much as the machine

A heat pump installed in a poorly insulated home has to work against a constant leak of heat to the outside, forcing the unit to be oversized and reducing its effective performance. The indoor heat-distribution system also strongly shapes the real outcome: traditional radiators, historically designed to work with very hot water from a boiler, force the heat pump to bridge a larger temperature gap and therefore perform worse than with underfloor heating or with low-temperature emitters specifically designed to work well with this type of unit — though high-temperature heat pump solutions also exist, specifically designed to replace boilers without changing the existing radiator installation. In extreme outdoor cold, some systems incorporate auxiliary electric-resistance backup for the most demanding peak loads, depending on how each specific unit is sized.

What to check before installing

  • The building comes first: seal air leaks and improve insulation before sizing any unit; a home with thermal leaks forces the heat pump to be oversized and penalizes its performance.
  • Compare real seasonal performance (SCOP), not just the COP measured under laboratory conditions at a single temperature.
  • Check the heat-distribution system: underfloor heating or low-temperature emitters perform better than radiators designed for very hot water, though high-temperature units exist that are specifically designed to replace boilers without touching the existing radiators.
  • Ask about the refrigerant: choose options with lower global warming potential and demand an installation that minimizes leak risk.
  • Factor in the outdoor unit's noise and the physical space it needs; a geothermal installation adds the cost of drilling wells or trenches.
  • "300% efficient" with no further context is not an annual promise: it depends on the climate, the flow temperature the system demands, and the unit's maintenance.

A simple rule

Do not compare only the purchase price: compare the total cost over the service life — unit, installation, electricity consumed, maintenance and refrigerant — against the alternative you are replacing.

The numbers, with their source

Three to five times more efficient than a gas boiler

According to the International Energy Agency (IEA), heat pumps available on the market today are between three and five times more energy efficient than a conventional gas boiler. A typical household heat pump has a coefficient of performance (COP) of around 4: for every unit of electricity the compressor consumes, it delivers roughly four units of useful heat indoors, because most of that heat comes from the outdoor environment it is extracted from, not from the electricity consumed.

Source: IEA — The Future of Heat Pumps, executive summary.

The refrigerant's global warming potential matters if it leaks

The R-410A refrigerant, historically widely used in this type of equipment, has a global warming potential (GWP) of 2,088; the R-32 refrigerant, increasingly common as an alternative, has a GWP of 675, about three times lower. Comparative studies also show that replacing R-410A with R-32 can improve the cycle's capacity and performance by 9% to 10%. The United States banned the installation of new R-410A equipment starting in 2025.

Source: technical comparisons published on ScienceDirect on R-32 and R-410A in heat-pump cycles.

What this table is missing

A laboratory COP measured at a single temperature is not the same as the real seasonal performance (SCOP) a specific unit will achieve in a given climate, home and heat-distribution system: that specific figure only comes from a local simulation or measurement, not a generic catalog number.

Sources

  • The IEA analyses this technology's role in The Future of Heat Pumps and keeps updated data in Heat Pumps — Energy System.
  • The US Department of Energy explains the fundamentals of seasonal performance in its technical guide to heat pumps.
  • Comparative studies published on ScienceDirect document the performance and global warming potential of alternative refrigerants such as R-32 versus R-410A.