PHAM NEWS | MARCH 2025 32 Ventilation & Heat Recovery


Combatting mould and condensation


Managing condensation in homes requires a multi-faceted approach, with the right balance of heating and ventilation. Nicola Rivers, indoor climate specialist at Zehnder, highlights the key issues that need to be addressed.


I


t is essential that we insulate our homes to keep heat in, correct? It has become the building mandate for years now.


But how often are we thinking about the effect this has on the air inside the house? By sealing our properties up


tight without also considering effective ventilation in parallel, we are essentially creating airtight boxes to live in. As a result, the property is not able to breathe, and stale air and excess moisture gets trapped inside causing an ideal environment for mould and condensation outbreaks. No building is immune


without expert help to keep the air inside refreshed. So, we need to ask what practical steps professionals in this sector can take to help homeowners combat the issue.


Condensation issues Excess humidity build-up in a property, combined with a lack of adequate airflow to ventilate that moisture effectively, causes condensation to form on cold surfaces, turning water vapour into liquid. Routine activities such as boiling a kettle, cooking, bathing, showering, and even breathing can produce significant amounts of water vapour – up to 24 pints per day for the average family – and without means to remove it, it becomes too heavy to stay in the air and settles on cold spots, often on windows or sills. These damp conditions provide


the perfect environment for mould and mildew to develop,


Plumbing and heating engineers are well placed to be on the lookout for tell-tale signs that the workings of a home are not in balance


which can have a serious impact on the building’s structural integrity and the health of those inside. Persistent condensation on


walls and ceilings in colder weather can damage interior finishes and the prolonged moisture accumulation can then lead to the decay of building materials. Over time, this deterioration can weaken structural components, resulting in costly repairs and jeopardising the safety of the house. Condensation-induced


Nicola Rivers Indoor climate specialist at Zehnder Group UK


moisture also undermines the effectiveness of insulation materials, reducing their thermal performance and in turn defeating the point of insulating for thermal efficiency. This constant battle between warm indoor air and cold external surfaces leads to increased energy demands for heating, driving up energy costs and putting strain on building systems. But most alarmingly, the


conditions allow for toxic black mould to take over, which poses a serious health risk to humans, especially those with low immune systems or the vulnerable like children or the elderly. The spores released into the air can lead to a variety of respiratory problems and allergic reactions among occupants.


Balancing act Managing condensation in homes requires a multi-faceted approach and the right balance of heating and ventilation. Upgraded insulation must be considered in partnership with an effective ventilation system to help regulate indoor humidity levels and promote a healthy indoor environment, minimising the conditions conducive to condensation. Plumbing and heating


engineers are well placed to be on the lookout for tell-tale signs that the workings of a home are not in balance and be armed with the knowledge to make recommendations to optimise heating and airflow accordingly. Inspections and maintenance appointments are essential to identify and rectify potential


t Damp conditions provide the perfect environment for mould and mildew to develop if a room is not properly ventilated


p The Zehnder Unity CV2.1HT runs constantly and features an integrated humidity sensor to provide a boost when required


issues before they escalate, safeguarding the structural integrity of the building. Check the radiators – all


radiators should be clear of obstructions and working properly, providing optimum heat output. If the system is free of air after bleeding, it might need flushing to get rid of any sludge that has accumulated and affect performance. But also, be on the lookout for cold spots around the home. Are any of the radiators undersized or in the wrong position for the room to be heated effectively? If so, then upgrades might be required.


System upgrade Check the current ventilation system is working effectively – look at the property’s current system. Are extract fans and trickle vent systems turned off or closed? If so, this would compromise their ability to remove stale, humid air and allow fresh air to be brought in. They could also be obstructed


or old and need replacing. If fans are over 5 to 10 years old you might find a newer model will give better performance, less noise and increased efficiency. New fans on the market, like the Zehnder Unity CV2.1HT (see opposite page) run constantly with an integrated humidity sensor to give a boost, or more demand ventilation when it is needed, such as after showering or while drying clothes. They are whisper quiet and run at a minimal cost – less than £2 per year. Extract fans should also be cleaned regularly to keep them in good working order. Make sure fans are installed


correctly – we’d recommend that ridged or semi-ridged ducting is used for all extract fan installations where possible. Flexible ducting should be


avoided, however if used it should be installed as straight and taut as possible, avoiding any bends or creases that might restrict airflow and affect the fan’s performance. Check for clear air paths into the property for ventilation systems to work properly. Trickle vents in windows and the use of undercuts on doors are good natural ventilation points but make sure these aren’t blocked by new carpets or furnishings or closed by residents.


It’s good to talk Talk to homeowners about their living habits – ask your clients about their behaviours and activities while at home. Drying washing inside, cooking for a large family multiple times a day and occupants taking long hot showers are all things that build up a picture of what humidity levels are like within the property and allow you to assess if the ventilation they have is sufficient. If necessary, you can then make recommendations on upgrades or provide advice on how to optimise the system they already have in place. As trusted experts,


professionals can help people living in these conditions understand how effective ventilation solutions can prevent condensation and improve overall indoor air quality. By offering clear advice and tailored recommendations, specialists can bridge the gap between awareness and action. Collaboration with builders, architects, specialist consultants, and manufacturers will also be essential in addressing this issue. There is a severe health risk


associated with damp living conditions and this common crisis needs to be solved – now. This is not a one size fits all approach, rather it requires a collective effort from across multiple industries and trade to truly influence change. ◼ phamnews.co.uk/325/52


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