While heat pump uptake in Europe is uneven, the common thread between the clusters is that heat pumps are on the rise everywhere. 

Despite assertions that suggest the opposite, heat pumps are common in colder climates. Europe’s heat pump powerhouses are northern European countries where temperatures are frequently below 0℃. 

The most prevalent type of heat pump in Europe is air-to-air, dominating heat pump powerhouse and surger countries. Air-to-air heat pumps are cheaper and easier to install than air-to-water heat pumps but they are not always used for space heating. In heat pump cooler countries, primarily in southern Europe, air-to-air heat pumps are used as air conditioning units to provide space cooling. 

On the other hand, this review shows that the transition to air-to-water heat pumps might be a harder journey. While it might be anecdotal, all countries in the heat pump latecomer category rely primarily on air-to-water heat pumps. This is not to say that it is wrong for those countries to depend on air-to-water heat pumps. It is also unclear from the data whether the countries installing air-to-air heat pumps are using them for heating rather than cooling purposes. 

Preference for air-to-water heat pumps is also a matter of tradition and policy decisions. In the UK for example, most households already have radiators and want to continue heating their homes in this way. Additionally, the UK’s flagship Boiler Upgrade Scheme policy only offers grants for air-to-water and ground-source heat pumps, not air-to-air heat pumps. The prevalence of air-to-air heat pumps in Scandinavian countries where they are used for heating purposes shows that they should not be discounted as an alternative way to heat homes and accelerate the rollout of heat pumps.