Active vs passive cooling on heat pumpsCompressor cooling vs natural cooling — how they differ
Heat pumps can cool a home in two ways: active cooling, which runs the compressor, and passive cooling, which does not. They suit different systems and deliver different results. This page compares them and explains which Vaillant systems support each.
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Active cooling
Active cooling runs the heat pump compressor in reverse to actively chill the water sent to your indoor units. It delivers stronger, more controllable cooling and works on air-source systems such as the aroTHERM. It uses more electricity than passive cooling because the compressor is running.
Passive cooling
Passive cooling moves heat from the home into a cool heat sink — typically the ground, via a ground-source heat pump’s buried collector or borehole — without running the compressor for cooling. It is very cheap to run, but the cooling effect is gentler and depends on having a suitable ground loop.
Vaillant offers an official passive cooling module for flexoTHERM and flexoCOMPACT ground-source systems.
A side-by-side summary. The right choice depends on your heat pump type and what is already installed.
| Aspect | Active cooling | Passive cooling |
|---|---|---|
| Compressor | Runs for cooling | Not used for cooling |
| Typical heat pump | Air-source (aroTHERM) and others | Ground-source (flexoTHERM) |
| Cooling strength | Stronger, more controllable | Gentler |
| Running cost | Low — but higher than passive | Very low |
| Main requirement | Cooling resistor + activation | Suitable ground loop |
Frequently asked questions
Which is better?
Neither is universally better. Active cooling gives stronger cooling and suits air-source heat pumps; passive cooling is cheaper to run but needs a ground loop and gives gentler cooling.
Which does an aroTHERM use?
The aroTHERM range is air-source and uses active cooling. Enabling it needs the cooling resistor fitted and cooling activated by an installer.
Do both need a coding resistor?
The cooling resistor sold here authorises active cooling on compatible aroTHERM and VWL units. Passive cooling on ground-source systems uses Vaillant’s separate passive cooling module — check your model’s documentation.