Impact of Indoor Humidity in Winter

Low indoor humidity is a common problem during winter. The lack of moisture in your indoor air can cause dryness and aggravate allergies and cold symptoms. However, for those who live in a high-humidity area, even the cold winter days can be uncomfortably damp or clammy due to excess moisture. Humid conditions can also trigger allergies and lead to mold growth. To remain comfortable and healthy, indoor humidity must kept at around 30% to 50%, depending on the ambient temperature. 

Both too little or too much humidity can have negative effects on your health and surroundings. It’s essential to control humidity levels, especially during extreme weather conditions. Due to the lower temperature during winter, the ideal indoor relative humidity levels must be lower than the humidity the rest of the year. For instance, 50% during summer may be acceptable, but in the winter, this level may cause discomfort. 

What is Humidity?

First of all, you must understand that there will always be some amount of water vapor in the air long as there is heat and a water source. The total volume of water vapor in the air is what we usually refer to as the absolute humidity. As a general rule, higher temperature means the air can contain more water. And if the outdoor air is humid, then the indoor air is likely also humid. 

What is Relative Humidity?

When measuring humidity levels, we typically use the relative humidity (RH). It is the ratio of the actual amount of water in the air compared to the maximum amount it could hold at a given temperature. Additionally, the dew point is the temperature at which the air becomes saturated or unable to hold more moisture, reaching 100% relative humidity.

The relative humidity is higher when the actual temperature is closer to the dew point. Thus, the relative humidity may be higher in cold air when the moisture level does not change. For the same reason, high relative humidity can make high temperatures seem warmer. 

humidity measurement during winter

What is the Ideal Indoor Humidity in Winter?

The ideal relative humidity level is around 30% to 50%. To remain comfortable, humidity may be adjusted within this range depending on the ambient temperature and personal preference. In most cases, 30% may be considered too low, but when the temperature drops below freezing point, you may be more comfortable in humidity levels no higher than 30%.

Generally, humidity levels above 50% is considered high. Humidity around 55% to 60% may still be acceptable for some in warm, sunny days, but usually, higher humidity can make the warm air feel warmer than it actually is. Furthermore, high indoor humidity can lead to mold growth and pest infestation over time. 

Effects of Low Indoor Humidity in Winter

Remember that the colder winter air is naturally able to hold less moisture and humidity levels below 30% to 40% are normal, depending on actual temperature. Any tiny gap in your home insulation can allow the cold, dry air outdoors to seep inside the the house, resulting in dry indoor air. Low humidity indoors can cause static electricity to build up, increasing the risks of shocks when touching metals or another person.

Dry air absorbs moisture from any moist surface it comes into contact with, including your skin, eyes, and nasal passages. This can dry out your skin and cause itching and flaking. Low humidity in the winter can also cause nasal congestion due to inflammation, scratchy throat, and other common cold and flu symptoms. 

Nevertheless, if  the outdoor temperature is between 20ºF and 40ºF, it’s recommended to set your indoor humidity no higher than 40%. If the outdoor temperature is between 10ºF and 20ºF, indoor humidity must be no higher than 35%. If the outdoor temperature is between 0ºF and 10ºF, indoor humidity must be no higher than 30%. If the outdoor temperature is below 0ºF, indoor humidity must be 25% or lower.


Effects of Low Indoor Humidity in Winter

Effects of High Indoor Humidity in Winter

High humidity relative to the temperature can create an environment that is unpleasant for you but suitable for harmful organisms. In the summer, humidity levels around 50% to 60% may be acceptable, but beyond this, it can be extremely uncomfortable. When the relative humidity is high, the temperature feels even higher because the air is already saturated with moisture. Your sweat can’t evaporate into the air and it makes your body feel even warmer. 

Even in winter, when relative humidity is higher than the ideal levels we discussed above, it can feel damp and clammy. Besides causing discomfort, it can also lead to serious health problems. High humidity breeds mold, dust mites, and other microorganisms. Mold spores and dust mites are some of the common allergens that may trigger allergy symptoms, asthma attacks, and other respiratory issues. 

Musty smells, condensation on windows, and water stains on walls and ceilings are some of the most common signs of high humidity. Mold and mildew grow on almost any moist surface and feed off of organic matters such as wood, fabric, and soft furnishings. This can damage your furniture, carpets, flooring, and your very house structure. Mold growth is commonly found in dark, damp areas such as bathroom walls, under sinks and toilets, behind furniture, or beneath the carpeting. It can be even worse in a cold climate because mold likes damp, cold, and dark areas.  

Effects of High Indoor Humidity in Winter

Effects of Low Humidity in Winter

In many parts of the world, the air does tend to be cooler and more moist during the winter. If it’s especially cold and a heater is constantly running, it can actually make the air uncomfortably dry.

How to Maintain Proper Indoor Humidity Levels in the Winter

It may be much easier if you have a hygrometer, humidistat, or any other device that can measure relative humidity to monitor your indoor conditions. In case the humidity reading reaches 50% or higher (at temperatures between 10ºF and 20ºF in winter), then you need an effective humidity control solution. Depending on the level of humidity, you may need to install an electric dehumidifier to help reduce indoor humidity.

A dehumidifier effectively maintains proper indoor humidity levels by extracting moisture from the air. If you have extreme cases of high humidity in the winter, you may need a specialized dehumidifier made to operate in lower temperatures. Typically, a dehumidifier is useful during hot, humid summers, but you can find desiccant units that are useful at any time of the year, although usually at a higher price. Dehumidifiers come in different types and sizes suitable for a variety of your specific needs. 

If you don’t want to use a dehumidifier during this time because of concerns regarding the purchase and operation costs and maintenance requirements, you may also find alternative ways to help maintain proper indoor humidity. The most common method is to simply open your windows, but this definitely isn’t a good idea during winter if it’s cold and/or wet in your area. If excess moisture is your problem, try natural desiccants or moisture absorbers such as rock salt, baking soda, calcium chloride, and silica gel. Unlike most electric dehumidifiers, desiccants can continue to work in cold weather.

On the other hand, if the indoor humidity is lower relative to the indoor temperature, then you need to increase humidity instead of reducing it. This usually happens when you use a heater or furnace during winter, which can dry out the air too much. In this case, you may need a good humidifier to add the right amount of moisture to the air and maintain proper humidity levels.

You can use a furnace humidifier that connects directly to your heater and to manage humidity across your house. Alternatively you can use warm mist or cool mist humidifiers in specific rooms depending on your preference. Whether you need to use heating or air conditioning, you can run it on low or use a fan to help regulate the humidity levels and temperature at the same time.

How to Maintain Proper Indoor Humidity Levels in the Winter


Ideal humidity levels vary from winter to summer, and unbalanced humidity levels can make the cold weather even harsher. To improve indoor air quality and your overall comfort, it’s essential to control both the temperature and relative humidity.

Again, the ideal humidity is relative to the ambient temperature, but in general, high relative humidity can make any temperature seem higher than it actually is. To prevent discomfort and especially the harmful effects of improper humidity, it should be maintained around 30% to 50% depending on the ambient temperature. In winter, humidity levels lower than 30% may be acceptable, but watch out for the common signs of low humidity such as dry skin and stuffy nose.

Likewise, be wary of the symptoms of high humidity such as musty odors and allergies. If necessary, use either a dehumidifier or humidifier to help maintain the right humidity level in your home throughout the winter season.

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