One of the greatest advantages of heating with an air-conditioning system is that, under the right conditions, it can generate a significant amount of heat using relatively little electricity. A state-of-the-art inverter unit can therefore be a cost-effective alternative to traditional heating solutions in many homes, either alongside them or even in their place.
However, high efficiency alone does not guarantee a low winter electricity bill. Even if you have chosen the right appliance and it has been installed correctly, a few less obvious mistakes in how you use it can increase your consumption month by month without you realising it.
We have already discussed this in a previous article the most common faults with air-conditioning systems, such as incorrect sizing, incorrect temperature settings, inadequate air distribution and a lack of maintenance. This time, we’ll be looking at seven further faults with air-conditioning and heating systems that prevent them from being as energy-efficient as they could be.
Why might your air conditioning use more energy than you expected?
When choosing an air-conditioning unit for heating, technical specifications such as the COP or the SCOP. However, whilst these help to compare the efficiency of appliances under standardised conditions, actual winter energy consumption depends on many more factors than this.
For example, it matters whether the outside temperature, the building’s thermal insulation, the desired indoor temperature, and the unit’s current load, the air flow, the frequency of defrost cycles, and how we use the air conditioning on a day-to-day basis.
This is why two appliances of the same type may consume quite different amounts of electricity in two different homes. As in our article on the energy consumption of air conditioners As we have also explained in detail, it is not worth making assumptions about your expected electricity bill based solely on the rated power or a single piece of catalogue data.
7 air-conditioning and heating faults that few people think about
Mistake 1 – You rely solely on the temperature shown on the air-conditioning display
When setting the heating function on the air conditioner, you should check where the unit measures the set temperature of 22 °C. The indoor unit’s temperature sensor is located inside the unit itself, and as warm air rises, the temperature is higher near the ceiling than at the level of the sofa or desk.
Consequently, It may be the case that, according to the device, the room is warm enough, whilst the person in the room feels it is cool. In such cases, we set the air conditioning to a higher temperature, which leads to higher energy consumption. The vertical temperature difference can be particularly significant in rooms with high ceilings.
It is therefore worth checking the actual temperature using a separate room thermometer. With some air-conditioning units, operation can be controlled on the basis of a thermometer built into the remote control or a separate sensor, which allows for more precise comfort control in certain situations.
Mistake 2 – You set the temperature to drop too much overnight
It seems logical to assume that if we turn the heating down significantly overnight or whilst we’re away for a few hours, we’ll save more money. However, with air-conditioning-based heating, it’s not always that simple.
The air conditioning can heat the air up relatively quickly, but in a cold flat, the temperature of the walls and floor also drops. If we ask the unit to raise the temperature significantly in the morning, the air conditioner will have to run at high power for a longer period of time.
This does not mean that you should not turn the heating down at all, but it is worth experimenting with a slight reduction. The correct setting varies from building to building. A well-insulated house with a high thermal mass behaves quite differently from a building that cools down quickly. Therefore, rather than following a universal rule, it is worth monitoring actual energy consumption and comfort levels.
Mistake 3 – Expecting a single air-conditioning unit to heat the whole flat automatically
It is a common misconception to think that if a heater’s output is, on paper, sufficient for a given square metre, it will be able to heat the whole flat evenly. However, heat does not travel in square metres.
The air-conditioning unit in the living room will only supply an adequate amount of warm air to the adjoining bedroom and bathroom if there is a clear path for the air to travel through. A door that is half-open can significantly restrict air circulation.
If, at this point, we simply turn the temperature up further, the result will be that the living room becomes too hot, whilst the room further away will still not be particularly comfortable. Therefore When designing an appropriate climate control and heating system, it is necessary to take into account both the heating requirements of each room and the actual flow of air. From this point of view, the positioning of the air-conditioning unit in the flat is at least as important as the unit’s performance itself.
Mistake 4 – You’re blocking the flow of warm air with furniture or curtains
If there is a tall cupboard, a thick curtain or some other room divider „in front” of the indoor unit, blocking the airflow, the airflow will not be able to reach the further corners of the room properly. It is therefore worth checking where the air might be heading next.
Mistake 5 – You mistake the defrosting process for a fault and interfere with the operation
One of the most striking – and, at first glance, rather alarming – aspects of using an air-conditioner in winter is the defrost cycle. When operating in heating mode, frost or ice may form on the heat exchanger of the outdoor unit. Modern air-conditioning systems therefore automatically defrost the outdoor heat exchanger from time to time.
In such cases, the user may find that The supply of warm air stops for a few minutes. It is a fault if we regularly switch it off and restart it at this point or switch the appliance to a different operating mode because we think something has gone wrong. Doing so may actually disrupt the automatic defrosting process.
It is a different matter if the outdoor unit remains covered in a thick layer of ice for a prolonged period, if defrost cycles are unusually frequent or prolonged, or if you find that the unit is no longer able to heat as effectively as before. In such cases, it is advisable to have the system checked by a specialist.
Mistake 6 – You don’t pay attention to where the water from the outdoor unit goes
During defrosting, the ice that has built up on the outdoor heat exchanger melts. A clearly visible amount of water can be produced during each cycle, and this water needs to drain away somewhere. In sub-zero temperatures, this water may freeze again later.
If drainage beneath the outdoor unit is inadequate, gradually ice may form. This could cause a problem in the vicinity of the fan or the heat exchanger, and it also matters where the water flows to. If it freezes on the pavement, it can create a slippery surface that poses a risk of accidents.
For this reason, when an air-conditioning unit is used regularly for heating, the positioning of the outdoor unit and its drainage must be considered with winter in mind right from the installation stage.
Mistake 7 – You try to work out how much electricity the air conditioning uses just from your electricity bill
„My air conditioner uses a lot of electricity” – this is something you often hear, although in reality there are no specific figures on exactly how much electricity the appliance itself has used. In winter, we use more lighting, and the electric water heater and many other appliances may operate differently. There is therefore little point in comparing a mild November with a particularly cold January.
Some smart air conditioning systems also display estimated consumption data in their own app. A properly configured separate electricity meter can provide an even more accurate picture.
One of the best tips for air conditioning and heating isn’t actually a tip at all: measure before you jump to conclusions.
If, for example, you want to find out whether the night-time temperature reduction actually reduces your energy consumption, change only this one setting at a time, then monitor the results over several days, ideally when the outside temperature is similar.
Heating and air conditioning settings: a practical starting point for winter
There is no one-size-fits-all setting that works in the same way in every building and under every climate. The optimal strategy may differ between a well-insulated, newly built house and an old flat with significant heat loss.
| Setting or criterion | A good starting point | What should you pay attention to? |
| Operating mode | HEAT / heating | For winter heating, it is advisable to select the direct heating mode |
| Temperature | approx. 21–23 °C | Check the actual room temperature as well |
| Fan | AUTO or an appropriate medium setting | Insufficient air flow can impair heat distribution |
| Lamella | downwards, towards the interior of the room | If possible, avoid spraying directly onto people |
| Overnight collection | moderate | Avoid letting the temperature drop too much if you’ll need to turn the heating back on within a few hours |
| Interior doors | in accordance with the heating concept | Don’t automatically expect a single air-conditioner to heat several closed rooms |
| Outdoor unit | free air flow and adequate drainage | In winter, you need to watch out for snow, ice and meltwater |
However, these should be treated as a starting point. Setting the truly optimal heating and air-conditioning settings always depends on the building, the appliance, the weather outside and the occupants’ comfort requirements.
Air conditioning and heating tips: a 5-minute winter checklist
If you feel that your air-conditioning is using more energy than expected, you don’t necessarily need to assume there’s a complicated fault straight away. It’s worth taking a few minutes to check the following:
- Is there a free flow of air in front of the indoor unit?
- Is the temperature around the sofa, bed or desk really the same as that detected by the air-conditioning?
- Are you trying to heat too many separate rooms with just one indoor unit?
- Is the air duct of the outdoor unit clear?
- Can the water produced during defrosting drain away?
- Are the defrost cycles running smoothly?
- Do you have any figures on the air conditioner’s actual electricity consumption?
These simple air-conditioning and heating tips are more helpful than just fiddling about with the temperature and different settings at random.
When is high fuel consumption not caused by a setting error?
It is important not to try to solve every problem through user settings. If the system does not work properly even when used correctly, it may be that the device itself needs checking.
It is worth consulting a specialist if the air conditioner has been running at maximum capacity almost continuously for a long time but is still unable to reach the desired room temperature.
It may also be a warning sign, if the outdoor unit remains covered in ice for a prolonged period, if you notice unusually frequent or very long defrost cycles, or if you hear any unusual noises.
This may be due to incorrect sizing, installation problems, a lack of maintenance or a technical fault; however, it is also possible that the building itself is losing so much heat that the air-conditioning system can only compensate for this by consuming a significant amount of energy.
In such cases, rather than trying out one new air-conditioning „trick” after another, it is worth having the entire system checked by a professional.
Frequently asked questions about the economical use of air-conditioning for heating
What temperature should you set the air conditioning to when using the heating?
In many homes, a setting of between 21 and 23 °C ensures a pleasant level of comfort, but there is no single ideal temperature that suits everyone. What matters more is the actual temperature in the living area than the exact figure shown on the air-conditioning display.
Is it worth switching off the air conditioning at night?
Not necessarily. For short periods, it may often be more practical to reduce the temperature slightly rather than switch the system off completely.
Is it normal for the air conditioning to switch off from time to time whilst the heating is on?
Yes. In cold, damp weather, the appliance may occasionally carry out an automatic defrost cycle. When this happens, the flow of warm air may stop for a few minutes. This is not necessarily a fault in itself.
However, if the appliance fails to return to heating mode for an unusually long period, or if the problem is accompanied by any other fault, it is advisable to have it checked.
Is it normal for water to run from the outdoor unit in winter?
Yes. During heating operation, particularly during the defrost cycle, water may naturally form at the outdoor unit.
The problem arises when water drainage is not properly managed and ice forms when the temperature drops below freezing.
Can one air-conditioning unit heat several rooms?
In certain open-plan flats, a well-positioned air-conditioning unit can effectively regulate the temperature in several interconnected spaces. In the case of separate, enclosed rooms, however, the distribution of warm air is much less reliable.
Cost-effective space heating does not depend on a single „secret” setting
Heating with an air-conditioning system can indeed be an energy-efficient and cost-effective solution, but only if the unit, the building and usage patterns are considered together.
It is not enough simply to buy an air-conditioning unit with a suitable SCOP value. It also matters where the temperature is sensed, how the warm air circulates within the home, and what temperature changes we programme.
If you are currently planning to install an air-conditioning unit that can also be used for heating, you can prevent many future problems by ensuring it is correctly sized and positioned. SMARTAIR’s experts will assist you from selecting the unit to planning the installation, ensuring that your air-conditioning system operates efficiently even in winter.