Why do we talk about dry cold in winter?

The amount of humidity in the air is an important aspect for the indoor comfort of a house. Depending on the season, the humidity level can vary, as it is subject to different temperatures.

So why do we talk about dry cold in winter? How does it feel?

Dew point and relative humidity: explanation

There are several ways of expressing the amount of water vapour in the atmosphere and each has its advantages and disadvantages. Two of the most common are dew point and relative humidity:

• Dew point is the temperature to which the air must be cooled to be saturated with water vapour, assuming a atmospheric pressuree and a constant water content. Dew is formed when the air is cooled to the dew point temperature.
• Relative humidity is a percentage, defined as the ratio of the actual amount of water vapour in the air to the maximum amount of water vapour the air can hold. The maximum amount is a function of temperature.

Understanding the difference between dew point and relative humidity is important, as both measures of humidity in the air help us to better understand the feeling of dry cold and therefore the need to humidify the air or not.

Where does that dry cold feeling in winter come from?

When the dew point temperature is equal to the air temperature, the relative humidity is 100 % and the air is considered saturated with water vapour. The greater the difference between temperature and dew point, the lower the relative humidity.

Cold outside air entering your home is heated by your heater; this increases the temperature, but not the dew point. This leads to a decrease in the relative humidity in your house in winter, as the difference between the dew point temperature and the temperature of your house increases.

When the dew point is too lowIf you are not careful, your skin can become dry and itchy. Static electricity can also increase in your home. Clothes can stick to each other and you can feel static shocks when you touch something. This is called dry cold.

How can we make the air more humid?

Humidifiers add water molecules to the indoor air, which increases the dew point temperature and thus the relative humidity. This increases the dew point temperature and thus the relative humidity. This means that the humidity level can be adjusted to improve your thermal comfort. However, be careful not to over-humidify your house in winter: otherwise you risk feeling damp and cold if your house is not heated enough, and therefore feel colder.