Heat pumps and winter condensation: how to manage it to avoid problems

When winter is just around the corner and the cold starts to set in, your heat pump becomes your best ally in keeping indoor spaces comfortable and welcoming.

However, during the winter period you may notice the outdoor unit dripping water from underneath and wonder whether this is normal or a sign of a malfunction.

If you find yourself in this situation, there’s no need to worry: it is a very common phenomenon. In this guide, you will discover why heat pump condensation in winter is often perfectly normal, how to distinguish potential issues, and how to correctly manage the drainage of the water produced, ensuring your system always delivers optimal performance.

The heat pump is leaking water: condensation or a fault?

The first thought when faced with a heat pump leaking water in winter is that something is wrong. In reality, in most cases what you are seeing is NOT a leak, but simply condensation.

Winter condensation in a heat pump is a completely expected by-product of how the system operates, especially during colder periods. In any case, knowing how to distinguish between condensate drainage and a real leak is useful, so you can take action when needed and maintain maximum system efficiency.

In the following sections, you will learn how to understand when water discharge is normal and when, instead, you should be concerned.

Why does a heat pump produce condensation in winter?

To heat your home during the colder months, the heat pump extracts thermal energy from the outdoor air. In doing so, the air—rich in moisture—comes into contact with the cold coil of the outdoor unit.

This causes an effect very similar to what happens when you take a cold bottle of water out of the fridge: the moisture in the air turns into tiny droplets on the cold surface. This explains why heat pump condensation appears as water collecting underneath the unit.

There is therefore no reason to worry: seeing water beneath the unit means everything is working as it should.

From ice to water: the defrost cycle

When outdoor temperatures drop below zero, the condensation generated by the heat pump can freeze on the outdoor unit’s coil. Over time, a layer of frost (or even solid ice) can form on parts of the unit, hindering proper heat exchange.

The defrost cycle was designed precisely to prevent this issue: it is an automatic process in more advanced HVAC systems that melts the ice and restores the unit to optimal operating conditions.

How does defrost work?

Let’s take a closer look at how the defrost cycle works in the two main types of heat pumps:

• Compression heat pumps: to defrost, these units “reverse” the thermodynamic cycle for a few minutes, directing heat to the iced coil and melting the frost. During this phase, efficiency may temporarily decrease and you might notice a slight reduction in heat output.
• Absorption heat pumps (such as those by Robur): here, defrosting takes place without reversing the cycle, avoiding thermal imbalances and maintaining optimal indoor comfort.

In modern heat pumps, a defrost valve is always present: a key component that regulates the cycle and ensures uniform and safe defrosting.

Remember: the water you find beneath the unit, especially after a very cold night, is often the result of frost melting during the defrost cycle. It is therefore a sign that the system is operating correctly.

How to properly manage and drain condensate water

Although it is normal to see water under the heat pump in winter, it is important to ensure that the heat pump condensate drain is correctly installed and compliant with regulations.

Here is what you can do:

• Install dedicated channels and drain pipes to direct the water towards soakaways or drainage areas.
• If necessary, use specific collection kits designed to handle large volumes of condensate.
• Check that the water path is not obstructed by ice, leaves, mud, or other debris.
• Avoid direct discharge onto pavements or roads: under certain conditions this could create dangerous ice patches.
• Condensate water is clean (it does not contain harmful chemical agents), so it can be sustainably discharged into the ground or designated collection points, always in compliance with local regulations.

In any case, the most advisable option is to rely on an experienced installer, especially during the initial installation phase, who will be able to recommend the best way to manage condensate.

Condensation vs leakage: how to recognise a real system issue

Of course, not all “water leaks” are the same. If you suspect that your heat pump is leaking water from underneath but are unsure whether it is condensation, here is a simple test to clarify any doubts:

1. Switch off the heat pump for 30–60 minutes.
2. Check the outdoor unit and the area underneath: if the water stops accumulating, it is almost certainly operational condensation.
3. If the water continues even when the unit is switched off, there may be a fault (damaged pipes, faulty fittings, internal pump issues, etc.).

Other potential warning signs include:

• The presence of water even when the system has been off for many hours.
• Unusual noises, a burning smell, or alarms displayed on the unit.

In these cases, it is best to contact a qualified technician immediately.

Prevention and maintenance for optimal operation

Careful maintenance of the outdoor unit and the heat pump condensate drain helps prevent anomalies and extends the lifespan of the system.

Here are some useful tips:

• Periodically check that channels and drain pipes are free from blockages (ice, leaves, mud).
• Regularly clean the outdoor unit of dust, debris, and weather-related buildup.
• During very cold winter periods, make sure that the condensate drain does not freeze (if it does, prompt action is required to avoid system shutdown).
• Rely only on qualified personnel for scheduled maintenance checks: regular inspections can prevent costly failures or issues caused by accidental ice buildup.

By following these recommendations, you can ensure a healthy, warm indoor environment and long-term system efficiency.

What about heat pump condensation in summer?

Not only in winter! Even during the warmer months, a heat pump can produce condensation. What’s the difference?
During cooling operation, condensation forms inside the indoor unit, while the outdoor unit remains warm. It is the same physical phenomenon that occurs on the glass of a cold drink on a hot, humid day: moisture from the indoor air settles on cold surfaces.

So, if you find water near the indoor unit in summer, there is no cause for concern.
Summer condensation in a heat pump is another normal manifestation of system operation, this time related to cooling rather than heating.

How much water can a heat pump produce through condensation?

One of the most frequently asked questions concerns the amount of water produced by a heat pump. The short answer: it depends.

The main factors are:

• Outdoor temperature: the colder it is, the harder the heat pump works, and the more condensate is produced.
• Relative air humidity: more humid air generates more condensate than dry air.

Indicatively, a heat pump operating in winter conditions can produce:

• From a few litres to more than 10–15 litres of water per day, in situations with very cold and humid air.

This value may increase for large-capacity units or under climatic conditions particularly favourable to the phenomenon.

In summary

If you notice that your heat pump is leaking water in winter, it is most likely simple condensation produced by normal operation and the defrost cycle.
By correctly managing the heat pump condensate drain, carrying out regular maintenance, and taking a few simple precautions, you can enjoy comfort and energy savings with complete peace of mind.

Still have questions about your heat pump?

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