Air-to-air vs air-to-water heat pump

Technically they are family: an outdoor unit extracts heat from outside air, even in frost, and a refrigerant carries that heat indoors. The difference is what happens inside. With air-to-air, an indoor unit releases the heat directly into that one room with a fan. Colloquially such a system is simply called an airco; Vereniging Eigen Huis (Dutch) explains that every fixed AC unit with a heating mode is in fact an air-to-air heat pump.

With air-to-water, the heat goes into a water circuit: your radiators, your underfloor heating and a storage tank for hot tap water. That way the system takes over the role of your gas boiler, partly (hybrid) or entirely (all-electric). Which is exactly why the two are hard to compare on price alone: they solve a different question.

The overview below sums up the practical differences. Watch the rows on tap water and coverage in particular: they decide whether a system can truly replace your boiler or stays alongside it.

For an air-to-water heat pump, hybrid or all-electric, you can apply for the Dutch ISDE subsidy. For an air-to-air heat pump you cannot: RVO (Dutch) explains that under European rules this type falls into the air conditioning category and is mostly used for cooling, which increases energy use rather than reducing it. That missing subsidy makes the price gap between the two routes smaller than the bare purchase prices suggest.

We deliberately leave out amounts: they change per year and are published by RVO and in your quote. When you calculate an air-to-water system, look at the whole picture: unit, installation work, possibly a storage tank, minus subsidy, set against what you save on gas.

If summer cooling matters as much as winter heating, the air-to-air heat pump plays a home game. Cooling is its original profession: the same indoor unit that blows warm air in January cools a bedroom or office noticeably within minutes in July.

An air-to-water system can sometimes cool too, but gently: through the underfloor heating the floor gets a few degrees cooler, which feels pleasant on hot days but does not replace an AC unit. People who want both regularly end up with a combination: air-to-water for heating and tap water, and a separate AC unit for the attic or bedroom.

If you want to make your whole home sustainable and eventually get off gas, air-to-water is the route. The follow-up choice, hybrid next to your boiler or straight to all-electric, mainly depends on your insulation and heat delivery; that trade-off is covered in hybrid vs all-electric and the insulation requirements in insulation and heat pumps.

If it concerns one room, an apartment without space for heating system changes, an attic office or a home where cooling weighs heavily, an air-to-air system can be the smarter and cheaper choice, even though we do not supply those ourselves. We install air-to-water heat pumps, and we will say so honestly when your question fits an AC specialist better. Put your situation to us or read on first on our heat pump page.