Heat Sources for Heat Pumps

What Are Heat Sources in Heat Pump Systems?

A heat source is the place where a heat pump gets its energy from. Instead of creating heat by burning fuel, a heat pump takes existing heat from the environment and moves it into a building.

This environmental heat can come from:

  • Outdoor Air
  • The Ground
  • Water Sources
  • Waste Heat from Technical Systems

The heat source is always outside the building and acts as the starting point of the heating process.

Why Heat Sources Matter

The heat source determines where the heat pump collects energy before sending it into your heating system.

It influences:

  • How much heat is available
  • How stable the temperature is throughout the year
  • How the system behaves in different seasons

The heat source affects how the system interacts with the environment, not how the heat pump works internally.

The basic working principle stays the same,  only the place where the heat is taken from changes.

How Heat Sources Are Classified

Heat pumps can be grouped in many ways. One of the most important ways is by heat source type.

This classification simply answers one question:

i.e. “Where does the heat come from?”

It does not describe:

  • How the heat pump is built
  • How it is installed
  • How efficient it is
  • What type of building it is used in

Those topics are covered on separate pages.

Main Heat Source Types for Heat Pumps

Air as a Heat Source

Air-source systems take heat from the outdoor air. Even cold air contains usable thermal energy.

This is the most common heat source because outdoor air is available almost everywhere.

LEARN MORE: Air Heat Source

Ground as a Heat Source

Ground-source systems collect heat stored in soil and rock layers below the surface.

The ground temperature stays relatively stable throughout the year, which provides consistent heat supply.

LEARN MORE: Ground Heat Source

Water as a Heat Source

Water-source systems use water bodies such as groundwater, lakes, or rivers as energy sources.

Water can store large amounts of heat and often offers stable operating conditions.

LEAR MORE: Water Heat Source

Waste Heat as a Heat Source

Waste heat systems recover unused heat from industrial processes, ventilation systems, or technical infrastructure.

Instead of letting this heat escape, it is reused for heating purposes.

LEARN MORE: Waste Heat Sources

Heat Source vs Heat Pump Technology

Heat source describes where the heat comes from. Heat pump technology describes how the heat is transferred.

No matter which heat source is used, all heat pumps rely on the same physical working principle. Changing the heat source changes the energy supply location — not the core heat pump technology.

If you want to understand how heat pumps work internally, see:

Heat Pump Technology

Heat Sources and Heat Pump Types

Heat pump systems are often described using multiple characteristics at the same time. These include:

  • Heat source type
  • System design (for example split or monoblock)
  • Temperature range
  • Application area

Heat source pages explain only the origin of environmental heat. Combined system classifications are covered on the heat pump types pages.

Heat Pump Types Overview

How Heat Sources Fit Into the Heating System

From a system perspective:

  • The heat source is outside the building
  • The heat pump collects and upgrades heat
  • Distribution systems deliver heat inside the building

This separation allows the same heat pump technology to work with different heat sources without changing how the system fundamentally operates.

Heat sources define where a heat pump collects its energy from. Common heat sources include outdoor air, the ground, water, and recovered waste heat. The heat source affects how the system interacts with the environment but does not change how the heat pump works internally. Understanding heat sources helps explain how heat pumps use environmental energy for heating and cooling.

Based on your location, space availability, and building type, different heat pumps are available based on heat sources.

Air (Ambient Air Source)

Air source heat pumps extract thermal energy from outdoor air and transfer it into the building heating system. They require no ground works and are suitable for most residential installations.

Ground (Vertical Boreholes)

Ground source heat pumps use geothermal energy from deep boreholes. Underground temperatures remain stable throughout the year, providing consistent heat supply.

Ground (Direct Evaporation)

Direct evaporation systems collect heat directly from the soil using buried refrigerant loops. This method enables efficient heat absorption without a separate brine circuit.

Flat Collector (Ground)

Flat collectors use shallow ground layers as a heat source. Horizontal pipe loops are installed below the surface to absorb stored solar and environmental heat from the soil.

The collector area must remain open and unsealed so the ground can regenerate heat naturally through sunlight and moisture.

Water (Groundwater)

Groundwater heat pumps use underground water layers as a stable heat source. Thermal energy is extracted via a production well and returned to the aquifer through a reinjection well.

Because groundwater temperatures remain relatively constant year-round, this heat source provides highly stable operating conditions.