What’s the Ideal Indoor Humidity and How Can It Be Managed?

Comfort and indoor air quality (IAQ) are both linked to key elements that can improve our experience with air conditioning: temperature, ventilation, and humidity. The latter is an element that sometimes gets overlooked in households. Humidity deeply affects our feeling of temperature, as higher humidity levels can make the environment feel stuffy and uncomfortable, while low humidity enhances cooling. There is of course an ideal range that reduces the impact of humidity on comfort.

In this article, we will be focusing on humidity, for comfort and health, its impact, and ways to manage it to suit household needs.


What is Relative Humidity?

When we talk about humidity, we are referring to the presence of water vapour, or moisture, in the air. Water evaporates from any source of water when heated, whether it is from directly boiling a pot of water in the kitchen, or from hanging wet laundry indoors, and the surrounding air then holds it. Warm air can actually hold more moisture than cool air; so to measure humidity in a practical way, we use the term relative humidity (RH), which is the water vapor concentration in the air in relation to the temperature. Relative humidity is expressed as a percentage; for example, 50% RH means that half of the volume of air consists of water vapor.


To measure relative humidity indoors, a hygrometer or a humidity monitor is used. They provide humidity readings for the room where they are installed. It’s recommended to install them away from known humidity sources, windows, heaters, etc because their accuracy can be affected by surrounding factors.



The Ideal Indoor Humidity Level

What is the ideal range of humidity indoors? According to the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), indoor relative humidity should be kept below 65%, to prevent mould growth, and to maintain comfort. Their guidelines do not specify a minimum value, but they advise monitoring any comfort-related issues, such as skin or eyes dryness, and nasal or throat irritation, which indicate humidity is too low.


The Occupational Safety and Health Administration (OSHA) recommends a relative humidity minimum of 30% and a maximum of 60%, which ensures comfort for most people in the office setting, although this can be applied to other indoor spaces, such as homes.


The Environmental Protection Agency (EPA) comments that, ideally, relative humidity indoors should be kept below 50% whenever possible, to discourage pests attracted to moisture. The minimum they recommend is 30% RH.


As relative humidity takes into account temperature, these general recommendations can be applied all year round. However, for more accurate values, optimum relative humidity during summer is around 40%-50%, and during winter between 30%-40%. Most people feel comfortable in these ranges, but individual preferences may be different, so it is a case of finding the range that suits you best.


Humidity Through the Seasons



Effects of unsuitable humidity levels

Now that we have a better idea of what the ideal humidity level is, let’s take a look at the effects of relative humidity when it is too high and when it is too low. We consider that humidity is too high when it is over 80%, and too low when it is below 20%, at these values the negative effects of unsuitable humidity levels are more pronounced. Both situations pose some health-related issues, but there are also some symptoms that can be observed in our homes and furniture.



What happens when there is too much humidity?


When a space has too much humidity, it can easily manifest in the form of mould or mildew growth. Dark spots may start appearing in ceilings, wall paint can start to bubble up or chip off, and wood furniture can start to show moisture stains or, worse, rot.

Condensation and rust around electrical components and appliances are also caused by an excess of humidity. It can cause electrical malfunctions, raising the risk of short circuits and fire.

Excessive moisture also attracts pests, such as insects, rodents, and mites that need water to survive.

The effects of high humidity on our health are just as serious: respiratory infections, worsened allergies due to the presence of mould or mites, more frequent asthma flare-ups, respiratory tract irritation, etc.



What happens when there is too little humidity?


When humidity is too low, the effects can be seen on wood flooring and furniture, which may start creaking, showing cracks or discoloration. Wallpapers start peeling off, while wall art, books, and photographs can also suffer chipping, discolouration, or become brittle.


With low humidity there is also more static electricity, which can damage appliances and exposed cables, increasing its risk as a potential electrical and fire hazard.


Healthwise, low humidity can cause respiratory irritation and infection, sore throats, eye dryness, nosebleeds, dehydration, eczema flare-ups, and skin irritation, which can show up like dry skin or chapped lips.



Health and Humidity Levels




Humidity, mould, and allergens 

The presence of mould or mildew lowers our home’s IAQ, causing respiratory issues and allergies. High humidity is the main culprit for bacterial or mould growth. To keep them at bay, it is important to monitor humidity and keep RH below 65%, as per ASHRAE’s guidelines, or below 50%, the recommendation of the EPA. With existing mould or mildew issues, you may need to inspect the source of humidity in the affected room or area, then look at your options to improve it or get rid of the root cause.  


In the case of existing dust or seasonal allergies, humidity can also play a role in aggravating these. When humidity is very low, allergens and particles easily flake off and can stay longer floating in the air, instead of settling down on flat surfaces. Because of this, many allergy sufferers can find their symptoms worsen in low-humidity conditions.


On the other hand, too much humidity can also be detrimental to people with allergies. Even though humidity makes particles and allergens clump up and remain on flooring and other surfaces, very humid environments are ideal for mites and other allergen-carrying insects. So, there can be a higher presence of allergens in high-humidity spaces.


The key is to keep RH at a level that does not invite mites, mould spores, and other allergens, and at the same time keeps dust particles away from the air. This balance is achieved between 40% and 50% RH, according to the Clinical Research Centre.




Humidity and sleep 

According to the Sleep Foundation, high humidity increases wakefulness, reducing the time of crucial sleep stages when recovery and memory consolidation happens. Low humidity does not seem to have any direct impact on sleep, but the health issues we listed above can make it more difficult to get a comfortable sleep. They indicate that the ideal range of humidity for sleep is around 40% to 60%.


However, there are many other factors that affect the quality of our sleep, check our article on improving your sleep with environmental adjustments for more information and tips.



Household Sources of Humidity 

As we mentioned earlier, any body of water in our homes can evaporate and become water vapor, adding up to the humidity levels. Aside from that, what are other household sources of humidity? Let’s take a look at some of the most common ones:

  • Cooking without ventilation. Even if you are not boiling a pot of water, any type of cooking (baking, frying, microwaving, etc.) produces steam and humidity, along with other fumes. This is why it is so important to have exhaust fans or an overhead range hood or extractor hood in the kitchen.

  • Hot showers and baths. Steamy hot showers can feel comforting and relaxing on a winter day, but they produce a lot of steam that gets into every crevice, condensing especially near corners and other hard-to-reach places. Turning the exhaust fan on or opening a window to let the water vapour escape is helpful, but you will need to pay special attention to those nooks and crannies while cleaning the bathroom area, to prevent any chance of mould growth.

  • Leaky taps and pipelines. Mould and water damage around sinks are not uncommon, but it can be prevented. Periodically checking the sealing of water pipelines, such as around sinks and wash basins, and maintaining taps will avoid humidity issues.

  • Hanging laundry indoors. Some homes do not have balconies or exterior spaces to hang wet laundry, and hanging it indoors may become the easy solution, however, it can cause excess humidity. If there is no other viable alternative, such as a tumble dryer, wet laundry indoors is best hung in a room that can be closed off from the rest of the house and either with a window or exhaust fan turned on to get rid of moisture.

  • Appliances malfunctioning. Some appliances, such as refrigerators, dishwashers, washing machines, and air conditioners, if not maintained properly can have issues with excess moisture or water leakage. Schedule regular revisions to prevent any malfunctioning keep them running as efficiently as possible, and don’t delay any repairs or servicing.



Natural Ways to Manage Humidity 

To lower or increase humidity, a humidifier and a dehumidifier can be used to adjust humidity, and are very useful for extremely dry or extremely humid environments, or situations where accurate humidity control is needed. However, many households need minor humidity adjustments that can be done naturally.


How to lower humidity naturally:

  • Encourage natural ventilation through windows and doors.
  • Remove rugs and other unnecessary decorative textiles.
  • Hang laundry outdoors or use a tumble dryer.
  • Let more sunlight in.
  • Get humidity-absorbing plants: such as English ivy, peace lily, Boston fern, to name but a few.
  • Place a box or bowl of baking soda or rock salt near windows in humid rooms. 


How to increase humidity naturally:

  • Boil more water.
  • Take hot showers with the door open.
  • Place bowls or pans of water around the room.
  • Introduce houseplants (watering and misting keeps them healthy and add moisture to the air).
  • Dry your clothes indoors.
  • Get decorative and install a small indoor fountain.



Hitachi Solutions for managing humidity


Air conditioners not only provide comfort by adjusting the temperature to your liking, but they also treat the air by removing excess moisture and filtering allergens and other particles.


In the Hitachi Residential Air Conditioning ranges, the Dry Mode is ideal for quickly removing excess humidity from your space by just pressing a button. Another key feature is mould guard, a function that periodically dries the AC’s internal components, to prevent the growth of mould and other moisture-loving bacteria.

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