Condensation is a physical process through which a substance changes from its gaseous phase to its liquid phase. It is the reverse of evaporation or vaporisation.

The process of condensation often involves the cooling of the vapour until it reaches a temperature at which its gaseous molecules lose enough energy to change back into a liquid. This transition typically occurs when the vapour is in contact with a cooler surface. It also occurs when the temperature of the surrounding environment drops.

For instance, when you see water droplets on the outside of a cold drink, that’s condensation. The air around the cold drink cools down, and the water vapour in the air changes to a liquid state. These form droplets.

Condensation plays a crucial role in the water cycle on Earth. The process is responsible for the formation of clouds. The warm, moist air rises, cools and then condenses to form tiny water droplets, which come together to form clouds. When these droplets become too heavy, they fall as precipitation (rain, snow, etc.).

Condensation is also used in numerous industrial processes. This includes the condensation of steam in power plants, or in distillation processes, where it’s used to separate mixtures.

Where does condensation occur?

Condensation commonly occurs in various parts of a home, particularly in areas where warm, moist air comes into contact with cooler surfaces. Here are a few examples:

1. Windows and doors: On colder days, you might notice water droplets on the inside of your windows or glass doors. This is because the warm, moist air inside your home can condense on the cooler surface of the window or door.
2. Bathrooms: After a hot shower or bath, the bathroom often becomes filled with steam. When this warm, moist air encounters the cooler surfaces of mirrors, windows, or walls, it can condense into water droplets.
3. Kitchen: Cooking can release a lot of moisture into the air, which can then condense on cooler surfaces.
4. Walls and ceilings: If a room has poor insulation or ventilation, condensation can form on its walls or ceilings, especially during colder months. This is more likely to happen in rooms where more moisture is produced, like bathrooms and kitchens.
5. Basements and garages: These areas can often be cooler than the rest of the house, and thus, more susceptible to condensation, especially if they are poorly ventilated.
6. On pipes: Cold water pipes can cause condensation, as the cool surface of the pipe causes the water vapour in the warmer surrounding air to condense.

In many cases, regular condensation can lead to problems like mould or mildew growth. This occurs especially if and when the condensation is not managed effectively.

Potential health problems

Condensation itself is not directly harmful to health. It is a natural process and you experience it in many situations, like seeing your breath on a cold day or when water droplets form on a glass of ice-cold drink. However, persistent and excessive condensation in homes can lead to problems that may impact health. Here are two key ways:

1. Mould and mildew: Excessive condensation can lead to damp conditions, particularly on walls, ceilings, and around windows, which can be ideal for the growth of mould and mildew. These fungi release spores into the air, which can trigger allergies or exacerbate existing respiratory conditions like asthma. Some moulds, such as black mould (Stachybotrys chartarum), produce toxins that potentially cause more severe health issues, although this is generally rare and requires prolonged exposure.
2. Dampness and respiratory issues: Living in damp and cold conditions, caused by excessive condensation, may also lead to respiratory problems. Damp environments are conducive to dust mites and certain bacteria. These impact indoor air quality and potentially lead to or worsen respiratory issues.

How can you stop condensation?

There are several strategies you can use to reduce or prevent condensation in your home:

1. Improve ventilation: Good ventilation is essential for preventing condensation because it allows humid air to escape and fresh air to enter. Install exhaust fans or vents in rooms that produce a lot of moisture, like kitchens and bathrooms. When weather permits, open windows to help exchange moist indoor air with drier outdoor air. Cross-ventilation, where you open windows or doors at opposite sides of your home, can be particularly effective.
2. Use dehumidifiers: Dehumidifiers work by removing excess moisture from the air. They can be particularly useful in damp basements, large bathrooms, or other areas of your home prone to high humidity.
3. Insulate your home: Adding insulation to your home’s walls, roof, and floors can keep them warmer. It reduces the likelihood of condensation, which tends to occur on colder surfaces. Double-glazing windows can also help, as it keeps the inner pane of glass warmer. Additionally, insulating cold water pipes can prevent condensation that may form on them.
4. Maintain a consistent temperature: Using a thermostat to regulate the temperature in your home can prevent rapid temperature changes that can trigger condensation. It is the contrast between cold surfaces and warm air that leads to condensation, so maintaining a steady temperature can help.
5. Avoid drying clothes indoors: When clothes dry, the water has to go somewhere. If you dry them indoors without adequate ventilation, it can greatly increase indoor humidity. If you must dry clothes indoors, do it in a well-ventilated room or use a vented tumble dryer that vents the moisture outside.
6. Cover pots while cooking: Cooking, particularly boiling, releases a significant amount of moisture into the air. Using lids on pots and pans helps contain this moisture, preventing it from increasing indoor humidity.
7. Maintain your heating and air conditioning systems: Regular maintenance includes changing filters and ensuring the systems are working efficiently. Air conditioning units, in particular, can help control indoor humidity as they remove moisture from the air while cooling your home.
8. Use moisture-resistant materials: In bathrooms, consider using water-resistant paint and installing tiles, which resist moisture well. In kitchens, materials like stainless steel, tiles, or specially treated wood resist moisture. Consider sealants for areas where water may penetrate, like around sinks, tubs, or showers.