Air conditioners: The most economical way of heating? Myth or Truth?

There is often a lot of "gossip" about what is the most economical source of heating for a space, which, depending on who spreads it, shapes it according to its benefit. A typical example is the "telemarketing" category ads which advertise various devices that simply "work wonders", devices that disprove any theory of physics, most notably that of the Energy Conservation Authority.

How does an air conditioner work?

Trying not to get into particularly technical information that will make you tired we will try to explain the operation of the air conditioner as simply as possible.

The property of the materials on which the principle of operation of air conditioners is based is the same that cools the skin when sweat, or even more so alcohol, evaporates on it.

This property of the material is called Latent Heat and is the energy that is "hidden" in the material, and that is needed or given by it to change its phase, e.g. from liquid to gas, without changing its temperature. For example in the case of water, when it is ice and we gradually increase the temperature, when it reaches 0οC it does not become water, but it needs a little more energy to start turning into water.

For air conditioners instead of water another substance is used in their piping, the coolant (FREON), which is a substance with a very low boiling point, ie temperature at which it is converted from liquid to gas. During this conversion, it removes (removes) temperature from the environment and through a fan transfers this coolness to the space.

An air conditioner works much like a refrigerator. It can only reverse its function to produce heating instead of cooling. Have you noticed that when a refrigerator is running, a black element behind it heats up?

Air conditioners (like refrigerators) are air-to-air heat pumps that operate on a perpetual cooling cycle during which the refrigerant (now FREON R32) is compressed in the compressor (external machine) condensed and liquefied to produce heat. It is then expanded in the expansion valve and gasified in the evaporator (internal machine) producing cooling. The operation is completely reversed by the existence of a "valve" so that heating can be produced inside the machine.

Air conditioners are based on the concept of Latent Heat. They use a coolant (FREON R32), which inside the machine evaporates and cools it. It then enters a compressor where it increases its pressure and consequently its temperature and is driven out of the house where it loses heat with the help of an external fan. Finally, the refrigerant passes through the expansion valve where it becomes liquid again at low temperature, is led back inside and so on. (Eternal Cold Circle). During the heating operation, the air conditioner simply reverses its operation.

Consumption of an air conditioner is the sum of the consumption of the compressor, fans and all electrical and electronic components of the device and has nothing to do with the direct production of thermal energy by converting electricity through resistors.

Coolants are not consumed by the air conditioner nor do they lose their efficiency. The only case of their reduction is the existence of a leak which rapidly reduces their air conditioner efficiency.
Coolants at ambient temperature are gaseous and odorless so it is impossible for the general user to recognize their leakage except from the extremely reduced efficiency of the air conditioner.

How do radiators with heaters work?

It is the most conventional way of heating by directly converting electricity into heating with the use of conductors which have difficulty in passing current through them (ohmic resistance) resulting in heating (imagine something like friction). The efficiency of this method and based on the principle of conservation of energy is the absolute 1. That is, for every 1KW of electricity we consume we receive a 1KW of heating.

Caution! In this method, there is no "magic" for any type of heater, so do not believe anyone and any post - ad that will try to convince you that one radiator "burns less electricity than another".

What is the SCOP efficiency index for heating & the SEER efficiency index for cooling?

SCOP: It is the total efficiency of the device in heating, which is defined as the ratio of the total annual need for heating to the total annual energy consumed in heating.


Thermal Emission (KW)

Energy Consuption (KW)

To understand what exactly this means, in the case of heating with resistors for a space that has an annual need for heating of 1000 KW the reason is as follows: SCOP= 1000 KW / 1000 KW = 1 SCOP

Respectively we could understand that for a modern Inverter air conditioner which according to its technical characteristics, has an index SCOP = 5 (hot zone) that for every 1KW of electricity it consumes it can deliver 5KW of heating. That is: SCOP= 5 KW / 1 KW = 5 SCOP

This means that for the heating of the same space, comparing an air conditioner with a efficiency factor of SCOP = 5 with a conventional radiator with resistors, we will have one fifth (1/5) of consumption, ie we will have up to 80% savings.

SEER: It is the total efficiency of the appliance, defined as the ratio of the annual cooling need to the total annual cooling energy consumed.

In the case of cooling, the performance comparison can only be done between air conditioners, as there is no other relevant means.

What is the difference between an ON-OFF air conditioner and a modern Inverter engine?

The simple ON-OFF air conditioner starts by heating with its nominal power and when the temperature rises to the desired level it stops. When the temperature drops just below the desired level it starts again until it reaches its target again and so on,

As a result, the room temperature is not constant, but has a variation above and below the desired, as in the adjacent figure:

Continuous stops of the ON-OFF air conditioner strain the various components of the air conditioner (compressor, expansion valve, etc.) and increase the operating cost of the air conditioner, since the starting current is a multiple of the operating current.

In the case of Inverter air conditioners, on the other hand, they can change the compressor speed and therefore adjust their power at any time according to the needs of the space. That is, for the same assumption above, the air conditioner starts its operation at full power (many times more than its nominal) and as the room approaches the desired temperature it gradually reduces its power until it reaches the desired point where at this point continues and works at the lowest possible power so that you do not change the room temperature and do not have to restart. Then the Inverter air conditioner fluctuates its power at all times in such a way that the room temperature remains as stable as possible.

n Inverter air conditioner, therefore, provides us with a high level of comfort conditions, since it achieves in the best way what is required, which is to achieve the desired temperature in the room.

Continuous operation of the air conditioner at low speeds is much better than intermittent, for two main reasons:

  • strain the machine less than the continuous stops and starts of the conventional ON-OFF.
  • our air conditioner works much more efficiently and economically.

The above operating mode is responsible for the very low consumption of Inverter air conditioners compared to conventional ON-OFF type.

Air conditioners can only be compared in terms of efficiency to other heat sources, because there is simply no other way to compare them in terms of cooling and efficiency for this function.

What does A +++, which we are looking for in the energy labels of an air conditioner, mean in simple words?

The energy category of each air conditioner is defined, depending on the SEER and SCOP prices according to the following table:

Energy Category

SEER in Cooling

SCOP in Heating


8,50 ≤ SEER

5,10 ≤ SCOP


6,10 ≤ SEER < 8,50

4,60 ≤ SCOP < 5,10


5,60 ≤ SEER < 6,10

4,00 ≤ SCOP < 4,60


5,10 ≤ SEER < 5,60

3,40 ≤ SCOP < 4,00


4,60 ≤ SEER < 5,10

3,10 ≤ SCOP < 3,40


4,10 ≤ SEER < 4,60

2,80 ≤ SCOP < 3,10


3,60 ≤ SEER < 4,10

2,50 ≤ SCOP < 2,80


3,10 ≤ SEER < 3,60

2,20 ≤ SCOP < 2,50


2,60 ≤ SEER < 3,10

1,90 ≤ SCOP < 2,20


SERR ≤ 2,60

SCOP ≤ 1,90

In order for an air conditioner to be allowed to be imported into the European Union, the SEER factor must be greater than 3.60 and the SCOP greater than 3.40

So does the air conditioner have the lowest energy consumption compared to other conventional heating devices?

Comparison with other heat sources:

So suppose we have the following data:

  • A house of 50 sq.m. with moderate insulation and need for heating 7000 KWh for heating a winter period.
  • That 1KWh in an alternative Electricity provider costs together with all taxes and other charges 0.15 € / KWh.
  • But to be fair we must also compare with the most common means of heating in Greece (unfortunately), Oil. Suppose that the price of oil today (01/04/2021) is 1 € / liter and that every liter when burned produces, with perhaps a very optimistic efficiency of 90%, 10KW (1Lt = 10KW, so 1 € = 10KWh heating ).
  • In the case of natural gas, which is available only in Athens and Thessaloniki, we found that the average cost of one KWh amounts to all other charges of € 0.055.
  • In the case of the heat pump, the same applies to the air conditioner with a different SCOP.

So let's start the calculations:

Air Conditioner: In order for an Inverter to give us 7000 KWh with an efficiency factor of 5, it will need to consume 7000 KWh: 5 = 1400 KWh of electricity. So 1400 KWh x 0.15 € = 210 €. So the cost is about 210 €.

Oil: You will need 700 Liters of oil, because each liter of oil gives us 10 Kwh (as we said we assume 90% efficiency). So the cost is about 700 euros with the current oil prices (1 € per liter).

Natural gas: Its current price is 0.055 € / KWh. For 7000 KWh, the cost is about 385 euros since 7000KWh x 0.055 € = 385 €.

Heat pumps: In order for a medium temperature pump to give us 7000 KWh (even with a efficiency factor of SCOP = 3.5), it will need to consume 7000 KWh: 3.5 = 2000 KWh of electricity. So 2000 KWh x 0.15 € = 300 €. So the cost is about 300 €.

* In this case, as in oil and gas, the losses of piping, transmission and circuit that are changed depending on the installation are not calculated.

Electric Bodies - Radiators: In the case of all those conventional electrical bodies that as we said its efficiency is the absolute 1 we will need to heat the house 7000KWh so 7000Kwh x 0.15 € the cost will be about 1050 €.

In all of the above, if it is taken into account that the spit wall type air conditioner lacks circuit losses as well as that each room is autonomous with its own digital thermostat, which means that it will consume exactly the energy needed to heat each room and nothing more, then you understand that in real situations the final economy may be even higher.

Pollution: Here perhaps a special mention should be made of a more general advantage of electricity and that is that of environmental pollution. How much electricity is polluted depends solely on the method of production and not on how it is consumed. Unfortunately in Greece its production is done with fuels such as lignite, oil, natural gas that burden the environment in the area where it is produced. Ideally, however, it was produced mainly by LTD then we would have a highly ecological medium.

After all, is air conditioning the most efficient and economical in consumption through space heating?

If we wanted to give a quick and simple answer then… Yes! It's true… air conditioners, and especially split type wall air conditioners, are the most economical we can choose for space heating.

Can I use the air conditioner only as a dehumidifier?

Almost all air conditioners today have a dehumidification function, ie they can also function as dehumidifiers. But here, too, attention is needed:

Air conditioners when operating as dehumidifiers:

  • They reduce the room temperature.

Air conditioners, because they have the compressor outdoors, do not produce this minimum total heating (equal to the consumption) produced by an autonomous dehumidifier, thus reducing the room temperature. This may be desirable and enjoyable in the summer but probably not in the winter. In addition, the dehumidification function to operate efficiently requires a room temperature above 18oC so if you use the dehumidification function of your air conditioner in winter, when the temperature starts to drop it will stop and the dehumidification will work. It is also considered quite energy-intensive in case another heating source is used for the room to simultaneously produce cooling for the air conditioner. Simply put, the dehumidification function of your air conditioner should only be used in summer.

  • The dehumidification function of the air conditioner has no humidity adjustment (humidifier).

In a classic and autonomous dehumidifier there is a choice of the desired percentage of humidity in the atmosphere. Air conditioners do not have this setting (only some very expensive and only in the cooling mode) so the dehumidification function works without adjustment with the result that many times we exceed the normal levels.

The air conditioners when they produce cooling at the same time remove the humidity of the room through the liquefaction that takes place in the cooling element of the internal machine. This is why air conditioners produce water that is drained through a pipe.