Autumn is here - which for some will mean misty windows and running walls! With the drop in temperature, this time of year sees the transition from open windows to firing up the heating which should help to keep internal moisture at bay. But where ventilation is lacking, closed windows can trap moisture in the home, which can condense on cold surfaces such as glass windows and cold external walls. Opening windows to vent areas isn’t a viable option in cold weather for various reasons, the obvious one being that it allows your central heated air to escape the property, but also allows cold and often moisture laden air to enter your home, compounding the issue. The solution is to install or upgrade to suitable mechanical ventilation and maintain a decent heated indoor temperature. Below are links to the various system collections that we will look at in this article as solutions to problems:
dMEV MEV dMVHR MVHR PIV
You can look to minimise the introduction of moisture into the building - however, with most of the sources originating indoors, this becomes a feat that is most certainly easier said than done once we look at the sources and what you would have to do to stem their introduction to your building. Let's dive into these sources and causes so we can see where moisture predominantly enters our living spaces and ways to combat damp in trouble-prone areas.
Under-heating Homes or Fluctuating Internal Temperatures.
Warmer air holds more moisture than cold air - in fact, for every 11°C drop in temperature, the air’s moisture-holding ability decreases by about 50%. This seems on paper to be to our advantage as the weather cools, but actually, this is where the issue lies. The warmer the air, the lighter and smaller the water molecules are suspended in it. This makes it easier to be removed through venting, but more importantly it keeps the moisture in the air in gas form and not on surfaces in liquid form. However, when this warm air meets either cold surfaces or colder air, the molecules start to condense by binding together and returning to liquid form from their gas form. This makes the water in the air heavier and more prone to fall and settle onto surfaces due to gravity. There is also the fast cooling and condensing action when it comes into contact with cold surfaces such as windows and external walls that are losing heat by being exposed to cold outside weather - think about the ice cold drink in summer, the outside of the glass almost instantly glistens with water droplets. This is known as the dew point, which occurs when cold surfaces meet humid warm air, depositing the cooled water vapour as liquid water on surfaces. Open windows - especially in bathrooms - during colder weather will not just allow warm air to escape, but will allow cold air to enter the room, creating a hot/cold air barrier, condensing the water in gas form faster. This creates more visible steam in the room as the water molecules bind together in the air, making the air heavier and therefore slower to be removed by an extractor fan and in the worst case scenario can settle in the room causing damp issues. Keeping a consistent warm temperature throughout your home helps maintain comfortable airbourne humidity levels and reduces nighttime temperature fluctuations, leading to less condensation.
Bathroom Usage
Hot showers and baths produce steam, which cause condensation and are one of, if not the highest cause of internal humidity. To minimise steam when bathing, start by filling the bath with cold water and then gradually add hot water, as this reduces the amount of steam released into the air compared to filling with hot water first. It is also advisable to reduce the temperature of your shower so that it is still comfortable but releases less steam into the atmosphere, reducing moisture content in the room. Make sure your bathroom extractor fan is clean and functioning properly to remove steam before it has a chance of turning into condensation. Consider the positioning of your fan - if possible you want the unit to be extracting from as close to the source of steam as possible. The further the moisture has to travel to the exit point, the more time and cold surfaces it has to come into contact with which can allow the air to cool and the moisture to condense before being removed. It is also vital that you make sure that there is an adequate return flow of air into the bathroom to replace the humid air being removed. If your fan extracts at 100m3/h, you need the equivalent air flow to be able to enter the room to replace it. This air should come from the rest of the house, ensuring that the air replacing the extracted humid air is warm so as not to speed up the condensation process - this is another reason to keep windows closed during colder weather as cold air will be drawn into the room causing the issues we mentioned above.
Drying Laundry
Drying clothes indoors, especially on radiators, can be a major source of condensation, but for many of us, there is little choice but to cover the radiators and clothes horses with damp clothing to dry indoors during the winter months. It is important to recognise that this is a significant contributor to indoor moisture production - for example, a single wet towel can release up to a litre of water into the air as it dries. It is therefore critical that thought is put into where and when clothing is dried in the home. We would suggest drying clothes in a room that has an extractor fan running, such as a utility room or bathroom, or even in the kitchen. As mentioned before, maintaining a constant temperature (preferably around 18℃) will help to keep the air and surfaces in the room warm enough to slow the condensation of moisture evaporating from the drying textiles. If possible, close the door to the room to isolate the drying clothes to help to reduce the evaporating moisture from spreading into the rest of the home - but remember to ensure that there is an adequate return flow of internal air into the room so as to not choke the extractor fan. This can also allow you to heat a single room if necessary rather than your whole house if you are trying to minimise your heating bill. Having an extractor fan that can be triggered by rising humidity will allow you to dry clothes at any time without needing to leave a light on to keep the fan unit running and can allow you to dry clothing overnight to maximise using off-peak energy to reduce your energy bills.
Cooking and Kitchen Use
When cooking or boiling water on the stove, steam is released into the air and can accumulate. By covering your pans with lids, you limit the steam that escapes and use less energy to prepare your meals. To manage excess steam, make sure to use an extractor fan and keep the kitchen door and windows closed while cooking. This prevents steam from spreading to other areas of your home, where it can quickly condense away from the heat and stops the afore-mentioned ingress of cold outside air. If you have a cooker hood extractor - make sure you use this while cooking - especially if your hood extracts externally. Positioning your kitchen extractor fan is also important. Ideally, in the same vein as for bathroom fan placement, the ideal installation will place the fan as close to the cooker and hob as possible. It is advisable to also locate your kettle and microwave in this area as well.
Breathing and Perspiration
Here’s one that you really can’t stop at the source! Every time you exhale a small amount of water vapour is released, and on average people typically breathe more than 20,000 times a day. Overnight, when temperatures drop and the bedroom door is closed, humidity can build up quickly, with exhaled water vapour and perspiration from inhabitants being one of the main causes of the condensation on your windows in the morning. PIV systems along with the afore-mentioned trick of maintaining a constant indoor temperature, paired with ultra-quiet dMEV units running as a continuous and controlled trickle vent, can help to reduce moisture build-up in problem areas.
In general, the biggest problem factor where accumulating damp is concerned comes down to poor ventilation. If air isn't circulating properly it can become stale and saturated with moisture. While extractor fans in bathrooms, kitchens, and other damp areas are important, if you're noticing condensation in places without a clear moisture source, whole-house ventilation may be a better solution. Systems like Positive Input Ventilation (PIV), work by drawing in fresh air from roof level and gently distributing it throughout your home to replace stale air and lower humidity and are a great option for retrofitting into existing homes. These systems are highly efficient and help balance room temperatures, improving energy efficiency and work brilliantly alongside dMEV units in strategic positions throughout the home such as bathrooms, utility rooms and kitchens. Other options that can help individual rooms, especially in more modern properties, such as dMVHR units both extract stale moisture laden air while introducing filtered and warmed air back into the space to help not only extract moisture but also circulate the airflow while minimising heat loss. In major renovation work scenarios, it is certainly worth looking at installing MVHR systems, but due to the invasive nature of the installation process needed for these systems, they are not usually suitable as a quick retrofit option. Overall, moving towards continuous running systems such as dMEV, MEV, dMVHR, MVHR and PIV systems will not only help to protect your property but will actively help to reduce and control moisture issues in damp-prone homes and spaces.