The short answer: if you want to cool your home in summer and heat a few rooms in spring and autumn, a split air conditioner is enough. If you are installing the main heating system of the home, will use underfloor heating or radiators, and want hot water from the same unit, the right choice is an air-to-water heat pump. The two actually work on the same principle; a split air conditioner is an air-to-air heat pump that gives its heat directly to the room air. The difference shows in how the heat is distributed around the home, how the unit behaves in cold weather, and in hot water.
Same cycle, different carrier
An air conditioner and a heat pump both carry heat taken from the outdoor air into the home, and they do it with the same refrigeration cycle: a compressor, two heat exchangers and an expansion valve. In an air conditioner, the heat is carried into the room by the air passing over the indoor unit's coil; each room gets its heat from its own indoor unit. In an air-to-water heat pump, the heat first goes into water, and the water is distributed to underfloor heating pipes, radiators, fan coils and the hot water tank. We explained the steps of the cycle in our article what is a heat pump, and the differences between air-to-air and air-to-water types in our article on types of heat pumps.
Comfort: warm air or a warm floor?
An air conditioner heats a room by blowing warm air. Warm air rises; the area near the ceiling warms up while the floor level can stay cool. While the indoor unit runs there is air movement and fan noise in the room. Fast heating is the air conditioner's strength, but when it is used as the main heater through a long winter, the draught and the feeling of dry air can become uncomfortable.
With underfloor heating, heat spreads from the whole floor at a low temperature and largely by radiation. The floor surface usually stays below 29 °C; the room warms more evenly from floor to ceiling, with no draught and no indoor unit noise. Radiators, depending on the water temperature, offer similar quiet and steady warmth.
Another difference shows during defrost. In cold, humid weather the coil of the outdoor unit ices up, and the unit defrosts for a short time. With an air conditioner, no heat reaches the room during this time and the indoor fan usually stops. In a water system, the heat stored in the floor, the radiators or the water in the tank makes these few minutes unnoticeable.
Domestic hot water
An air conditioner does not produce hot water. A household that heats its home with air conditioners still needs a combi boiler, an electric water heater or a solar system for bathroom and kitchen water. An air-to-water heat pump also prepares domestic hot water. The HİDRA indoor unit with tank brings heating, cooling and hot water together in one cabinet, with an 80–140 litre tank depending on its class. If there is a solar collector on the roof, the collector circuit is connected through the second pump in the unit; when the sun is not enough, the heat pump takes over. The HİD / HİT wall-mounted indoor unit does the same job with an external cylinder.
Capacity in cold weather
The capacity of any unit that takes heat from the air falls as the outdoor temperature drops, because the compressor has to lift the heat from a colder source to the same temperature. The heating capacity of residential air conditioners is usually given for +7 °C outdoor air; the capacity at −10 °C and the operating limit vary widely from model to model. Before deciding to heat a home with air conditioners, you need to look for these values in the catalogue.
With a heat pump, capacity is selected for the region's winter design temperature. That is why we divided the AD series by climate:
- Vaha: For coastal climates with mild winters; rated capacity at +2 °C outdoor air, R32 refrigerant.
- Poyraz: For transitional climates such as the Marmara region; 55 °C water at −7 °C outdoor air, R290 refrigerant.
- Boran: For long, harsh winters; 65 °C water at −25 °C outdoor air with a vapour injection compressor.
- Ayaz: For Eastern Anatolia and high altitude; 75 °C water at −30 °C outdoor air with an R290 + R134a cascade circuit.
The figures of the Poyraz 12 show why the design point matters: it delivers 15 kW of heating at +7 °C outdoor air and 12 kW at −7 °C. A system selected on the figure for a mild day falls short on the coldest days. You can compare the series side by side on our heat pump models page.
Cooling in summer
Cooling is easy for an air conditioner: the cold coil both cools the room air and removes its moisture. An air-to-water heat pump cools too, but the cold water needs a carrier to reach the room. Fan coils use water at around 7 °C, and like an air conditioner they dry the air. Underfloor cooling is quiet and draught-free, but limited: if the floor surface drops below the dew point of the room air, condensation forms on it. So the floor is fed with warmer water, the capacity stays low and the air is not dehumidified. In a humid coastal summer, underfloor cooling on its own is often not enough.
The number of outdoor units is another difference. A home in which every room is cooled by its own air conditioner ends up with several outdoor units on its facade. In a heat pump system, a single outdoor unit serves the whole home, and indoors a wall-mounted or tank-type indoor unit sits in a technical space.
How running costs work
Both units use electricity, and both give out more heat than they use. The main factor in efficiency is how far the cycle lifts the heat: the smaller the difference between the outdoor air and the temperature at which the heat is delivered, the higher the COP. To heat a room through a small indoor unit coil, an air conditioner condenses the refrigerant at a fairly high temperature. Underfloor heating, thanks to its large surface, makes do with water at 30–35 °C; this is the range in which a heat pump works most efficiently. In a radiator system that needs 55–65 °C water, this advantage shrinks.
The second factor is the operating pattern. A heat pump selected for the building's heat loss runs through the winter at low speed and for long, uninterrupted periods thanks to its inverter compressor; it does not keep stopping and starting. An exact comparison on the bill, however, depends on climate, insulation, the heating system and hours of use. We explained the assumptions behind this calculation in our article on heat pump electricity consumption.
Combining the two: HİDREM
Many homes have no fan coil system. Cooling with water needs fan coils and well-insulated pipes; adding this infrastructure to an existing building is often difficult. The HİDREM indoor unit with refrigerant cooling was developed for this situation: in winter it feeds the underfloor heating or radiators through the water circuit, and in summer it sends the refrigerant directly to wall-mounted air conditioner indoor units. The comfort of a water system for heating and the convenience of an air conditioner for cooling come together in one unit.
HİDREM has one more benefit in summer. A split air conditioner throws the heat it takes from the room into the outdoor air through its outdoor unit; HİDREM instead directs this heat into the domestic water in its tank. While cooling runs, hot water is prepared as well, with no extra energy used for it. The unit is made in five classes from 8 to 16 kW, its tank holds 80–140 litres, and it pairs with Poyraz, Vaha or Boran outdoor units.
Which one, and when?
- A split air conditioner is enough: If the main heating in winter comes from another system, a combi boiler for example, and what you need is cooling in summer and heating a few rooms in spring and autumn.
- An air-to-water heat pump: If you are installing the main heating of the home, have underfloor heating or radiators, and want hot water from the same system. The climate decides the series; the building's heat loss decides the capacity.
- An older building with radiators: Switching without replacing the radiators needs a high water temperature; the Boran series delivers 65 °C water and Ayaz 75 °C.
- A home without fan coils: HİDREM, to heat with water and cool with wall-mounted air conditioner indoor units.
- A cooling-led holiday home on the coast: The Vaha series; up to three indoor units can be connected to one outdoor unit.
For a quotation
Write to us with the province your home is in, its floor area and insulation, the existing heating system (underfloor heating, radiators or air conditioners only) and your hot water needs; we will work out together which series and indoor unit fit. For the details of capacity and indoor unit selection, see our guide to choosing a heat pump.