Air Conditioning as a Heat Pump: The Smart Heating System for Your Home

You open the patio door. Outside, the summer heat shimmers. In the living room, the air conditioning unit hums quietly away. Cool air flows through the room and perhaps you ask yourself: “Can it actually heat too?” The answer is: Yes, it can. And pretty well.

What many people do not know: Behind a modern air conditioning unit is a full-fledged heat pump, more precisely an air-to-air heat pump. In summer, it extracts heat from the room air and releases it outside. In winter, the whole thing simply runs in reverse. Then the system extracts heat from the outside air and brings it directly into the living space via the indoor unit.

The difference from the familiar air-to-water heat pump lies mainly in the structure. While classic systems distribute heat via radiators or underfloor heating, the air conditioning unit handles this through the heat exchanger installed inside.

These high-performance radiators are true space miracles: compactly built, but with a huge surface area. This means heating works efficiently even at low temperatures and without complex modifications to the existing heating system.

So anyone who already has an air conditioning unit can also use it sensibly in winter. And anyone who does not yet have one has the opportunity to make an affordable entry into heat pump technology. In this article, you will find out how air conditioning units work as a heating solution, what their advantages are and for whom the switch is particularly worthwhile.

Air conditioning unit as a heating heat pump – what is behind it

Everyone knows it: You switch on the air conditioning and the room becomes cool. But basically, an air conditioning unit works like a classic heat pump, except that instead of heating water, it heats the room air directly. This is why air conditioning units are also referred to as air-to-air heat pumps, since heat exchange on both sides, outside as well as inside, works via the air.

In cooling mode, the system extracts energy from the warm indoor air and releases it to the ambient air via the outdoor unit. In heating mode, the heat transport simply works in reverse.

Heat is extracted from the outside air even at low temperatures below 10 °C and blown directly into the room via the indoor unit. The technology behind it is mature and now works reliably even at sub-zero temperatures down to 20 °C.

The major difference from the air-to-water heat pump lies in heat distribution. While air-to-water systems have to be connected to existing radiators or underfloor heating, air conditioning units take on this task themselves. This happens with a permanently integrated heat exchanger in the indoor unit.

This basically works like a high-performance radiator, but is much more compact. Thanks to the fine fin structure, it achieves an enormous surface area in the smallest space. We made the effort and measured such a heat exchanger from a small heat pump.

The result: We arrived at seven square metres of surface area in a single unit. This means a relatively low flow temperature is enough to noticeably heat the room. That is exactly what makes air conditioning units not only efficient, but also particularly attractive for use in existing buildings.

Less technology, fewer errors: Heating more simply with air conditioning units

Another advantage: Air conditioning units are delivered as an industrially preconfigured complete system. The outdoor unit and indoor unit are perfectly matched to each other, the control technology is integrated and installation is comparatively simple.

This means that, unlike water-based systems with radiators, no buffer storage tank, no circulation pump and no complicated hydraulics are needed. Room-by-room heat load calculation, as required for air-to-water systems, is also eliminated. A rough estimate of the required heating output is absolutely sufficient.

Due to the low complexity, typical sources of error are avoided that can lead to efficiency losses with air-to-water heat pumps. For example, incorrectly sized radiators, uninsulated pipes in masonry or outdated hydraulics.

So you get a slim, powerful system that not only gives you cool rooms in summer, but also cosy warmth in winter.

6 advantages of heating with air conditioning units

1. You install the unit and heat without major conversions

Air conditioning units can in most cases be retrofitted quickly and easily. Compared with a classic heat pump, there is no need to intervene in the existing heating system, no new radiators and no removal of the old system. The unit is mounted on the wall, connected to the outdoor unit and electrically connected.

2. You avoid planning errors because everything fits together

A major plus is the coordinated system of indoor and outdoor unit. All components are industrially preconfigured to match each other, and the control system is integrated.

This significantly reduces the risk of planning or installation errors compared with an air-to-water heat pump, because incorrectly sized heating surfaces or unsuitable hydraulics do not play a role in air-to-air systems.

3. You do not lose heat on the way into the room

While with air-to-water heat pumps the heat first has to be transported through long pipework to the radiators, air conditioning units usually have only very short connecting lines between the indoor and outdoor unit.

This saves energy, because in old buildings many pipes run through walls or floors and are poorly insulated. Every metre of pipe means potential heat loss. With air conditioning units, this point is practically eliminated.

4. You save yourself the buffer storage tank and hydraulic balancing

With air-to-water heat pumps, additional system components such as the buffer storage tank are required. The hydraulic balancing is also a must that costs time and money. You need neither of these with an air conditioning unit with heat pump function.

This not only saves effort during planning, but also reduces the costs for additional components and their maintenance.

5. You convert your house step by step

Air conditioning units make a gentle switch possible. So you do not have to convert the entire house to heat pump technology. You can deliberately use air conditioning units where the greatest heat demand arises, for example in the living room or work area.

Additional rooms can be added later. This flexibility is a particular advantage in existing buildings if you do not want to or cannot immediately opt for a central solution.

6. You can continue using your gas or oil heating

If the old heating system is not that old yet, switching to an air-to-water heat pump is usually not worthwhile. By using air conditioning units for heating, you can simply continue operating the existing heating system.

Even with a small air conditioning unit, gas or oil consumption can often already be reduced by more than half. This reduces CO₂ emissions and heating costs.

Which types of air conditioning units are suitable for heating

Not every air conditioning unit is automatically suitable for heating, but most modern units already have the heating function integrated. Basically, you have two options if you want to heat your home with heat pump technology via air conditioning units: split air conditioning units and compact air conditioning units.

Both work according to the principle of the air-to-air heat pump, but differ in design, installation and application area.

Split units: Powerful with high comfort

Split air conditioning units consist of two components. The indoor unit brings the warm air into the room and the outdoor unit extracts heat from the outside air, which is then transported indoors.

If you want to supply several rooms, you can either install several individual units or use a so-called multi-split system. In this setup, one outdoor unit supplies up to five indoor units at the same time.

This solution not only brings visual advantages, for example because you do not have to hang an outdoor unit on every house wall. It also makes it easier to comply with noise protection requirements. Depending on the floor plan, the outdoor unit can be positioned so that it causes as little disturbance as possible or none at all.

If you want to air-condition and heat your entire house, you can also completely do without a classic oil or gas heating system with several split units, provided that the heating output of the installed units matches the heat load of the house.

For the power supply, a normal alternating current connection is sufficient for individual units. Only with multi-split systems with higher output may a three-phase connection be necessary, which must be installed by an electrician.

Important: Split systems contain refrigerant that is only filled on site. Therefore, installation may only be carried out by a certified specialist company, meaning a refrigeration technician with the relevant approval. Without this step, the unit may not be put into operation.

Compact units: For apartments and individual rooms

If you want to heat a single room, for example the living room or a study, a compact unit is often a good alternative.

These monoblock units work according to the same principle as split systems, but do without a separate outdoor unit. Heat exchange with the outside air is handled via a supply air and exhaust air opening in the external wall.

The entire technology sits in the indoor unit, which is mounted directly on the external wall. Two core drillings are enough to ensure air and heat exchange. An outdoor unit is therefore not needed. This saves space and makes installation relatively simple.

You do not need a refrigeration technician and in many cases no new cable either, because a conventional socket is usually sufficient. And if you currently still heat with night storage heating, you can use both the space of the night storage heaters and their power connection. Another advantage is that compact air conditioning units consume only half to one third of the electricity of a night storage heater.

Wall-mounted air conditioning units are suitable not only for single-family homes, but also for condominiums. Especially when the homeowners’ association cannot or is not allowed to agree on a central solution because it does not want outdoor units outside or has concerns about noise pollution. Because they are installed indoors, they can also be used well in dense developments.

And in difficult conditions such as old single-pipe heating systems, where central systems often reach their limits, they offer a practical alternative with comparatively little effort.

What does a heat pump air conditioning system cost?

The good news first: Air conditioning units with heating function are significantly cheaper than classic heat pumps. For comparison: For an air-to-water heat pump including installation, you usually have to expect 25,000 to 35,000 euros in existing buildings.

Depending on the selected technology, unit output, room size and installation effort, modern air conditioning units with heat pump technology usually cost between 2,500 and 3,500 euros per room (including material and installation).

The decisive factors are the output required per room and whether you choose a split unit or a compact unit. With split systems, there are additional costs for installation by a refrigeration technician and possibly for the three-phase connection. Monoblock units are somewhat cheaper because they do not require an outdoor unit or refrigerant lines.

Especially in existing buildings, air conditioning units for heating are the cheapest solution. In addition, you can start gently with a single unit. Test it and then gradually work your way through the rest of the building.

What consumes more electricity: air conditioning unit or heat pump?

Both air conditioning units and classic heat pumps are among the most efficient heating systems. They turn every kilowatt hour of electricity into several kilowatt hours of heat, provided they are used correctly.

Air conditioning units release heat into the room via their indoor units and thus avoid long pipe routes. Compared with classic air-to-water heat pumps, this reduces heat losses and improves efficiency (especially in old buildings). In addition, air-to-air systems work without a circulation pump, buffer storage tank or heating circuit distribution. This reduces heat losses and additionally saves electricity.

Both systems can work efficiently. Air conditioning units often have a small efficiency advantage in existing buildings for the reasons described above.

What are the disadvantages of cooling with a heat pump?

Many people first think of cold air in the room when they hear air conditioning, but rarely of the how. And this is exactly where the most common criticism lies: moving air and noise. During cooling, air is actively blown into the room through the indoor unit.

Sensitive people find the airflow unpleasant, especially if the unit is poorly positioned. Modern units can certainly be deliberately adjusted, but a certain air movement remains noticeable.

In addition: The fans make noise, not very loud, but still audible. Especially in quiet rooms or at night, this can be disturbing for sensitive people. Visually, you also have to come to terms with the indoor unit in the room. It is compact, but still visible. So anyone who prefers “invisible” heating and cooling will not always be happy with an air conditioning unit.

Nevertheless: Anyone who plans carefully, relies on quality and positions the unit sensibly will cope well with most of these points and, in return, gets a flexible system that works reliably in summer and winter.

When is use particularly worthwhile?

• Replacing night storage heaters: Three times more efficient

If you still heat with electricity, for example via night storage units, air conditioning units are a good alternative, as you do not have to install heating pipes and radiators. Switching to an air conditioning unit is also a real leap in efficiency. Modern compact systems work around two to three times more efficiently. Split units are even better.

Instead of converting electricity directly into heat, they extract heat from the ambient air. In many cases, the existing electrical installation can even continue to be used, saving effort and money.

• In apartments with individual gas heating or single-pipe systems

A central heat pump often reaches its limits in older apartment buildings, especially with single-pipe heating systems or decentralised gas boilers. Here, air conditioning units can be a pragmatic solution.

They can be installed apartment by apartment, independently of the overall system and therefore also as a possible alternative for homeowners’ associations. This also applies when there is limited space in the basement or when permits for outdoor units are lacking.

• Affordable entry into heat pump technology

Anyone who does not want to decide immediately on a central solution, also because the gas or oil heating system still works well, can start with a single air conditioning unit. You simply try the technology first in the main living spaces such as the living room or office, gain experience and retrofit more if needed. This is exactly what makes air conditioning units with heating function so attractive in existing buildings.

• Combination with other heat pumps makes sense

Air conditioning units initially only cover the space heating demand. For hot water, a domestic hot water heat pump can be a suitable supplement. In many cases, such solutions can be combined in a way that is eligible for subsidies, especially in renovations of existing buildings.

Heat pump air conditioning conclusion: Start flexibly into the future with air conditioning units

You do not have to switch everything over at once. Air conditioning units allow you to move away from oil and gas step by step, and without a major construction site in the house.

The units are compact, efficient and quick to install. You can start small, for example in the living room or home office, and expand later. Depending on what suits your house, everyday life and budget.

Especially in existing buildings, where underfloor heating, new radiators or insulation measures often cause high costs, air conditioning units are a cost-effective entry-level solution into heat pump technology. And because they not only heat but also cool, they offer additional comfort in summer.

If you also want to switch hot water production to a heat pump, you can sensibly combine air conditioning units with a domestic hot water heat pump.

Bottom line, you get a proven system that brings you more independence, less CO₂ and lower heating costs. A modern air conditioning unit is more than just comfort: It is a pragmatic step toward an energy-efficient future.

Image sources:

1. Featured image: Air conditioning as a heat pump (Adobe Stock)
2. Indoor unit and outdoor unit of a split air conditioning system (Adobe Stock)
3. Indoor unit of a split air conditioning system (Adobe Stock)
4. Outdoor unit of a split air conditioning system (Adobe Stock)
5. Multi-split systems can supply heat to up to five indoor units (Carsten Herbert)
6. Split system on the wall below the ceiling (Adobe Stock)
7. Compact air conditioning units below the window (1- NNOVA S. r. l.)
8. Compact air conditioning systems outside two ventilation openings (Innova S. r. l.)