Air Conditioning for Cooling and Heating
Description of a split air conditioning system in an attic apartment for cooling in summer and supporting heating in winter.
An air conditioner like that is also a heat pump. For the calculation of its performance, see heat pump calculator. The performance factor of a split air conditioner is approximately 5 for heating and approximately 10 for cooling.
Description: A split air conditioner consists of two units: an indoor unit that blows cold or heat into the room, and an outdoor unit that extracts energy from the outside air. These are connected by tubes, so a hole usually has to be drilled in the wall to install them.
Unlike an air-to-water heat pump, which heats the water in the radiators and water pipes in the home, this is an air-to-air heat pump that can not only heat but also cool. Other options that have nothing to do with temperature but can also be very useful include dehumidification and air purification.
Environmental aspects: Electricity (except for coal-fired power) is almost always cleaner than heating oil, especially when using green electricity (from solar, wind, or water), as is the case here. The refrigerant in the system is a potential problem, but only if it leaks into the environment. This can happen through improper installation or damage. This system uses R-32, difluoromethane. This was the best refrigerant available for such devices at the time of installation, September 2025. Even better would be R-290, propane, which is already available for air-to-water heat pumps and will likely be used in smaller devices of this type in the future. In this case, R-290 is preferable.
Special situation: A 35-square-meter attic apartment on the second floor. In summer, temperatures can reach up to 35 degrees Celsius. In winter, the entire house is still heated by an oil-fired boiler, which will be replaced by an air-to-water heat pump in the next few years. Since the heat pump has lower flow temperatures for heating and the radiator in the living room of the attic apartment is rather small, it would have had to be replaced with a larger one during the heating system replacement. This radiator replacement is unnecessary if the future heat pump can be supported by the air conditioning system for heating.
Indoor unit of the split air conditioning system in the attic apartment.
Outdoor unit of the split air conditioner on the ground in front of the house.
Current reports on the use of split air conditioning systems:
• November 21, 2025: -3 degrees Celsius outside temperature, the split air conditioner easily heats the apartment on its own.
• At the end of September 2025, a Mitsubishi Electric MSZ-LN25VG2 was installed by AllgäuKlima. Shortly thereafter, autumn arrived, with temperatures below 10 degrees Celsius outside. The split air conditioner easily takes over heating on its own in such conditions, without the oil heater. This works well in autumn, but when it gets really cold in the winter, it's more difficult. Reports will follow.
The warmth from the air conditioner is very pleasant due to the warm wind. After switching it on, it takes a few minutes for the apartment to warm up, first of course directly under the unit, from there the heat spreads to the farthest corners of the apartment. At current electricity and heating oil prices, heating with the air conditioner costs about half as much as with the oil heater!
Dehumidification works well. When the windows are closed, as it's damp and cold outside, and wet laundry is hanging in the bathroom, the unit brings the humidity back down to below 60 percent within a few minutes. For technical reasons, dehumidification and heating cannot be done simultaneously.
Thermal image of the split air conditioner at the end of November. Outside it was snowing.
Here you can convert metric units into customary and imperial units and convert temperature units.
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