Why it can happen and what you can realistically do about it.
Some homeowners notice more condensation or mould after installing a heat pump. This can be unexpected, as heat pumps are often seen as part of creating a more efficient and comfortable home. In most cases, the heat pump itself isn’t the direct cause — but the change in heating pattern can highlight or worsen existing issues in the property.
Heat pumps run at lower water temperatures than gas boilers and often run for longer periods. In homes with poor ventilation or high moisture levels, this can lead to more condensation forming on colder surfaces.
Radiators create some air circulation through convection. Underfloor heating produces gentler heat with less air movement. In some homes, this can mean moisture lingers in the air for longer.
Many older homes already have marginal ventilation, cold spots, or poor insulation. When the heating system changes, these issues can become more noticeable. Blocked trickle vents or inadequate loft insulation are common contributors.
Showers, cooking, drying clothes indoors, and even breathing all add moisture to the air. If this moisture isn’t ventilated properly, it can condense on colder surfaces — especially in homes that were previously heated intermittently.
Make sure trickle vents are open and extractor fans are working properly. Consider using a dehumidifier in problem areas during the first winter after installation.
Improving insulation in lofts, walls, or floors can help raise surface temperatures and reduce the chance of condensation forming.
Run bathroom and kitchen extractor fans during and after showers or cooking. Timer or humidity-controlled fans are often worth fitting if you don’t already have them.
If mould persists, it’s worth getting a damp and mould survey. Sometimes underlying issues like poor cavity wall insulation or rising damp need addressing.
Use our Heat Pump Estimator to better understand what to expect from a well-designed system.