How Do Air to Water Heat Pumps Work?
It sounds like complicated engineering, but the idea behind it is simple: an air-to-water heat pump works like a refrigerator, running in reverse.
Most people are happy to trust a heat pump once they understand roughly how it works — and the good news is that the underlying idea is genuinely simple. There's no flame, no combustion, and no fuel delivery to arrange. Instead, an air-to-water heat pump moves heat that already exists in the outside air into your hot water and heating system, using the same basic principle as a fridge, just working in the opposite direction.
The basic idea
A fridge takes heat out of its interior and dumps it into your kitchen — which is why the back of a fridge always feels warm to the touch. An air-to-water heat pump does the same job in reverse: it takes heat out of the air outside your home, even when that air feels cold, and delivers it into your water cylinder and heating system.
Step by step
Outside air is drawn in
A fan pulls ambient air in from outside, across the outdoor unit. It doesn't need to feel warm outside for this to work — there's usable heat energy in air right down to well below freezing.
Refrigerant absorbs the heat
That air passes over a coil containing refrigerant with a very low boiling point. The refrigerant absorbs the latent heat in the air and evaporates into a gas.
The gas is compressed
A compressor squeezes the refrigerant gas, which sharply raises its temperature — the same principle that makes a bicycle pump warm up as you use it.
Heat is transferred to your water
The now-hot gas passes through a heat exchanger, releasing its heat into the water circulating through your cylinder. The refrigerant condenses back to a liquid, and the cycle begins again.
Hot water, ready to use
That heat is now stored in your cylinder, ready for taps, showers, radiators or underfloor heating — exactly as if it had come from a boiler.
Why this makes heat pumps so efficient
Because the system is moving existing heat rather than generating new heat by burning fuel, a small amount of electricity can deliver a much larger amount of heat. Orca air-to-water heat pumps produce up to 5 times more heating energy than the electricity used to power them — an efficiency rate of 300–400% or more. Put simply, for every 1kWh of electricity that goes in, you get roughly 3–4kWh of heat out. No oil or gas boiler can match that — burning fuel is capped at close to 100% efficiency at best, because you can never get more energy out than the fuel itself contains.
Does this actually work in an Irish winter?
It's the question we get asked most, and it's a fair one — early heat pump models had a reputation for struggling in cold weather. Orca heat pumps operate independently down to −7°C, and as low as −15°C with the help of an integrated electric heater. Donegal, and Ireland generally, very rarely sees temperatures anywhere near that — so in practice, an Orca system just gets on with heating your water and home right through the winter without missing a beat.
For the full specification, guarantee terms and running-cost figures, see our Orca air-to-water heat pump page, or read how these efficiency figures translate into real running costs.