Humidity Sources In The Home

As the nights draw in and temperatures drop, it’s time to switch from open windows to switching on the heating to reduce indoor moisture. However, poor ventilation can trap moisture, causing condensation on cold surfaces like windows and walls. Opening windows isn't practical in cold weather, as it lets warm air escape and brings in cold air that speeds up the condensation process of the humidity already present in the home. Minimising indoor moisture is challenging, as most sources come from within the home from processes that are hard to eliminate. Let's explore the main sources of moisture and how it enters living spaces, as well as ways to tackle dampness in problem areas.

Inadequate Heating or Fluctuating Indoor Temperatures

Warmer air holds more moisture than cold air. For every 11°C drop in temperature, the air's ability to hold moisture decreases by about 50%. While this may seem beneficial in colder weather, it's actually problematic. Warm air keeps moisture in gas form, making it easier to vent, but when it meets cold surfaces or colder air, moisture condenses into liquid. This occurs because water molecules bind together, becoming heavier and settling on surfaces like windows and external walls. This is similar to condensation forming on a cold drink in summer, known as the dew point. Opening windows in cold weather not only lets warm air escape but also allows cold air in, causing faster condensation. This leads to more visible, heavier steam, making it harder for extractor fans to remove moisture, and potentially causing dampness. Maintaining consistent warmth throughout your home helps control humidity and minimises condensation by keeping both the air and surfaces warm enough to slow condensation.

Bathroom Use

Hot showers and baths generate significant steam, a leading cause of indoor humidity. To reduce steam, start filling the bath with cold water before adding hot, as this limits steam production compared to starting with hot water. Lowering your shower temperature can also reduce steam. Ensure your bathroom extractor fan is clean, functional, and positioned close to the steam source for optimal removal. The fan should have adequate airflow into the room from the rest of the home to prevent the fan underperforming (e.g. if it extracts at 100m³/h, an equivalent amount of air must flow into the room to replace it). Keep windows closed in cold weather to avoid pulling in cold air, which accelerates condensation.

Laundry

Drying clothes indoors, particularly on radiators, is a major source of condensation. A single wet towel can release up to a litre of water into the air. However, this is a necessity when drying outside is not possible during the winter months. To minimise the problems of moisture content from drying laundry, dry clothes in a room with an extractor fan, like a utility room, bathroom, or kitchen. Keep the room at a constant temperature, ideally around 18℃, to prevent moisture from condensing on surfaces and if possible, close the door to isolate the drying area, but ensure adequate airflow to support the extractor fan. Using a humidity-triggered fan allows clothes to dry efficiently, even overnight, while taking advantage of off-peak energy to save on heating costs.

Cooking

Cooking and boiling water releases steam that can accumulate indoors. Covering pans with lids reduces the amount of steam released into the indoor atmosphere and saves energy too. To manage excess moisture, use an extractor fan and keep the kitchen door and windows closed to prevent steam from spreading through the home and cold air from entering. If you have a cooker hood that vents externally, use it while cooking. If not, place the extractor fan near the stove, and position appliances like kettles and microwaves in the same area to efficiently remove moisture from the room faster.

Respiration and Perspiration

You can't eliminate moisture from breathing, each person exhales a small amount of water vapour with every breath into the atmosphere and on average we breathe out over 20,000 times a day. Overnight, when temperatures drop and doors are closed, this can lead to significant humidity buildup and condensation on windows. To mitigate this, you could install a PIV system to maintain a consistent indoor temperature whilst displacing the humidity in the building. Additionally, ultra-quiet dMEV units running as continuous, controlled trickle vents can help reduce moisture accumulation in problem areas.

 

The main issue with accumulating damp often stems from poor ventilation. Without proper air circulation, moisture can build up, leading to stale, saturated air. While extractor fans in bathrooms, kitchens, and other damp areas are crucial, persistent condensation in areas without obvious moisture sources may indicate a need for either whole-house ventilation or an additional room extraction unit to help control the issue.

Positive Input Ventilation (PIV) systems are effective for this purpose. They draw fresh air from the roof and distribute it throughout the home, replacing stale air and reducing humidity by displacing the internal air. PIV systems are efficient, improve room temperature balance, and work well with dMEV units in bathrooms, utility rooms, and kitchens to create a circulatory air flow.

For modern homes, dMVHR units can extract stale, moist air while introducing filtered, warmed air, helping with moisture control and air circulation in problem rooms. However, whole house MVHR systems, which are ideal for major renovations, are less suitable for quick retrofits due to their intrusive installation requirements, but can offer the best results for controlling your indoor air quality and moisture removal.

Overall, continuous ventilation systems like dMEV, MEV, dMVHR, MVHR, and PIV can effectively manage and reduce moisture issues in damp-prone homes as well as proactively protecting any home from developing future issues.