What exactly is a heat pump?

A heat pump is a heating system that takes usable heat from outdoor air, the ground, or water and transfers it into a building. In a heating project, the term normally refers to the full heating solution, not just the outdoor unit: source, machine, controls, and connection to the building’s emitters.

The key point is functional. A boiler produces heat by combustion on site. A heat pump works by moving heat that is already present in the environment, using a thermodynamic cycle powered by electricity.

In practice, the term usually covers three linked parts:

• the heat source: air, ground, or water;
• the heat pump unit itself: the machine that upgrades that heat to a usable temperature;
• the distribution side: for example underfloor heating, radiators, or sometimes domestic hot water production, depending on the configuration.

That is why a heat pump should be understood as a system choice, not only as a piece of equipment. In a renovation, it often means a change in how the building is heated overall. In a new project, it may be part of the base heating concept from the start.

If your project concerns a specific family of systems, the next useful term is often air-to-water heat pump, which is one of the most common variants in residential heating.

The term matters when heat-pump technology is part of the building’s actual heating strategy: replacing a boiler, defining a central system, or checking whether a project falls under a subsidy programme. It matters less when the device is only a local comfort appliance or a dedicated hot-water product.

In a heating project, “heat pump” usually applies in four situations.

First, it applies when the system is intended to provide the building’s main space heating. That is the clearest use of the term: the heat pump is the central generator that serves the dwelling or the building.

Second, it often applies when the same installation also covers domestic hot water. That does not change the basic meaning, but it does change the project definition. A heat pump for heating only and a heat pump for heating plus hot water are not always read in exactly the same way in technical documents or programme rules.

Third, the term matters when you are checking subsidy logic. Here, the wording becomes important because programmes may assess the project according to the exact role of the system: what it replaces, what part of the building it serves, and whether it is the main heating installation or only an auxiliary device. Those conditions can depend on the programme, canton, building type, and project state, so they should be checked case by case on the heating subsidies route rather than assumed.

Fourth, the term matters when comparing technologies during system selection. If one option is a true heat pump-based heating system and another is only a partial or local solution, the comparison is not neutral. The investment, integration, and expected use are different.

By contrast, the term is less precise when people use it loosely for any electrically powered heating product. That shortcut is exactly where many project errors begin.

A nearby term often causes confusion: thermodynamic water heater. It also uses heat-pump technology, but its role is narrower. A standard heat pump in a heating project is discussed as a space-heating system, sometimes combined with domestic hot water; a thermodynamic water heater is primarily discussed as a hot-water device.

The distinction matters because the same underlying principle does not mean the same project function.

This is a good example of how glossary terms work in real projects. Two devices can both rely on heat-pump technology and still belong to different decision categories.

If your question is mainly about hot water rather than space heating, the more accurate entry is thermodynamic water heater. If your question is about replacing the main heat generator of the building, “heat pump” remains the correct umbrella term.

The most common mistake is to label any electrically powered or thermodynamic appliance a “heat pump” for the purpose of a heating renovation. That shortcut creates bad comparisons and grant misunderstandings. The right question is not “does it use similar technology?” but “what exactly does it heat, and at project level?”

Two mix-ups appear again and again.

The first is confusion with reversible air conditioning or air-to-air units. These systems may use the same thermodynamic principle, but they are not automatically equivalent to a full central heating system for the building. In some projects, that difference changes both the technical discussion and the way support schemes read the measure.

The second is confusion with direct electric heating. Both run on electricity, but they do not follow the same logic. One is simply an electric heating method; the other is a system designed to transfer environmental heat into the building. Treating them as the same category usually leads to poor system comparisons.

Use this quick filter before calling a project a true heat-pump heating project:

• What is the system’s main job?

Whole-building space heating, or only hot water or room-by-room comfort?

• What heat source does it use?

Outdoor air, ground, or water usually points to a heat-pump logic.

• How does it deliver heat indoors?

Into a building heating system, or only through local air delivery?

• Is it the main generator or just an add-on?

Grant and project definitions often depend on that distinction.

• Are the programme rules written for this exact system type?

If support is part of the decision, verify the wording against the relevant programme conditions.

That last step is especially important. In heating, a close-enough label is often not close enough for a project file. If you need the next decision layer, compare system families in the guide to choosing a heat pump and then verify the applicable support conditions on the subsidies route.