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What Is the Ideal Indoor Humidity?

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What's the ideal number? Let's find out.

The humidity levels in your home are crucial determinants of your overall comfort. High humidity can result in mold and mildew. In contrast, too little humidity will lead to dry skin and potentially damaged furniture.

It’s essential to be aware of the ideal indoor humidity level. That way, you can make appropriate changes to better your comfort.

We’ll walk you through what the optimum humidity levels are and how to gauge them. We’ll also share the best ways to add or remove moisture to get to the best humidity level.

Key Takeaways

  • Ideal indoor humidity levels range from 30 to 50 percent, promoting comfort and preventing mold or dryness issues.
  • Gauge indoor humidity levels using an ice cube test or a hygrometer for more accurate readings.
  • To increase humidity in dry conditions, use a humidifier, air-dry clothes, and place bowls of water or houseplants around the home.
  • Lower humidity levels by using a dehumidifier, exhaust fans, air conditioning, and avoiding boiling water indoors.


How to Gauge Indoor Humidity Levels

Unless you have a sixth sense for humidity levels, determining the exact levels will require some testing and, perhaps, a tool. Of course, there are some telltale signs that your indoor humidity is out of whack (1):

  • Too much moisture: Early symptoms include fogging or condensation on windows and excessive moisture. A warning sign is mold starting to grow on the walls and ceilings.
  • Low humidity: Early signs are usually increased experiences of static electricity. You’re also likely to see dried or cracked paint and millwork in the long run.

There are two main ways to gauge indoor humidity levels:

The Ice Cube Test

The ice cube test won’t give you an exact humidity percentage, but it’s quick and will give you a general idea.

What You Need

  • A glass.
  • Three ice cubes.
  • Water.

What You Do

  1. Choose a room: Pick a room in your home to test the humidity. You can use any place except for the kitchen and bathroom. These locations won’t give you an accurate idea because they consistently use water.
  2. Place the ice cubes: Put the three ice cubes into a regular-sized drinking glass.
  3. Add water: Add enough water to cover the ice cubes and give it a gentle stir.
  4. Leave the room: After adding the water, leave the room for three to four minutes.
  5. Check your results: Return to the room when the time is up. If you see droplets on the outside of the glass, the humidity is high. If there is absolutely no condensation, it’s too low, and you should consider a humidifier. However, if there is just a little condensation, your humidity levels might be adequate.

Hygrometer

The ice cube test is suitable to provide a general idea of humidity levels. For accurate results, though, you’ll need a hygrometer.

The hygrometer will measure the water vapor or humidity in the surrounding air. Fortunately, it’s not a pricey investment. You can easily find an analog or digital one for as little as $10.

Use the hygrometer in different rooms in your home to determine the humidity. Some places may have a lower or higher reading than others.

What Are Optimal Humidity Levels?

Ideal indoor humidity should be around 30 to 50 percent (2).

As the weather changes from hot to cold, humidity levels do, too (3). This is often referred to as “seasonal humidity.” It affects your comfort and home, so it’s essential to manage accordingly.

During winter, the air is crisp, bitter, or dry. In the summer, it feels heavier, muggy, and sticky. These are perfect descriptions of humidity levels throughout the year.

Summer

During summer or warm months, the air contains more moisture. The increased moisture takes longer to evaporate, which raises humidity. This is why the air may feel sticky or heavy, which can cause us to sweat more (4).

In summer, you should keep the indoor humidity levels at 30 to 45 percent (5). Avoid having more than 50 percent humidity, which could lead to discomfort and mold.

To prevent an increase in humidity, use your air conditioner to remove excess moisture. You can also turn on the exhaust fans to air out heat.

In addition, if you have a dehumidifier, it can help decrease indoor humidity. Just be careful not to overuse it.

A big don’t during a humid summer day is to use a humidifier. Even if you have a cold or an allergy flare-up, keep it to a minimum of 30 to 50 percent humidity (6).

Winter

Growing up in the cold north, where winters are long and dark, your skin will know firsthand what low humidity means. Apart from boots and jackets, our winter essential was a deep moisturizer. Winter air can be unforgiving to exposed skin — it draws out most of the moisture, leaving a bitter, sharp atmosphere behind.

Therefore, during cold months, restoring moisture to the indoor air is crucial. Try to keep indoor humidity at around 40 percent. If higher, you’ll notice condensation on the windows, indicating that humidity levels are too high and could cause mold.

In the winter, take a portable humidifier from room to room. If applicable, consider investing in a whole-house humidifier.

Another excellent tip is to place houseplants around your home. These can add small amounts of moisture to the air.

One thing we always do when it’s cold is place small water basins near the heating system. You can get small hangable containers to hang on radiators — these work similarly to humidifiers.

Low Indoor Humidity

Problems Associated With Low Indoor Humidity

We tend to worry more about high levels of humidity than low levels, probably due to our fear of mold and mildew. Too little humidity, however, can have adverse effects on overall health as well as our home (7). Let’s break it down:

Low Humidity Effects on Health

Low humidity is sneaky. It can cause a variety of problems to our health since it creates an environment where bacteria and viruses thrive. Some ailments include:

  • Dry skin and lips.
  • Scratchy throat and nose.
  • Increased chance of developing colds.
  • Respiratory issues.
  • Bloody nose.
  • Lung and sinus problems.
  • Low body temperature.

Effects of Low Humidity on the Home

Over time, low humidity can also cause issues with the home. These include:

  • An increase in static electricity.
  • Shrunken, separating, or warping of wood floors and furnishings.
  • Wallpaper may peel and loosen.
  • Accumulation of mold behind loose wallpaper.
  • Overall compromised indoor environment.

How to Increase Humidity

Humidifier

A humidifier is one of the best ways to add humidity to your home. It distributes water into the surrounding atmosphere.

Depending on your needs and home, you may need a whole-house humidifier or simply a portable one. Small humidifiers are fantastic to have in the bedroom at night or in the corner of the living room. But, if your rooms are spacious and open, consider a large humidifier.

Air-Dry Clothes

One way to restore moisture to the air is by air-drying washed clothes. Instead of throwing your batch of laundry in the dryer, use a clothes drying rack where applicable. Doing this also saves energy, improving your utility bills and the environment.

Consider an indoor vent kit for your dryer if you don’t have time to wait for the clothes to dry. This will allow your dryer to vent indoors instead of out, improving the humidity level.

Place Bowls of Water on Register

Placing a bowl of water on the register is an easy but effective way of restoring humidity. Grab a metal or ceramic bowl, place it on the floor register and fill it halfway with water. As the register heats the water, it begins to evaporate, thus releasing moisture into the air.

If you have a radiator, try a hanging water basin. Look to change the water once a week or when it’s fully evaporated.

Leave the Bathroom Door Open

If possible, leave the bathroom door open during hot showers or baths. The steam from the water will seep through the door and blend with the atmosphere.

For our fellow bath-buddies, let the water cool down before you drain it. The warmth from the water rises and can increase the humidity a bit.

Watch Out For Small Children

If you have small children in the home, don’t leave any water in the bathtub unattended (8). This is a drowning risk.

Cook More

Increasing the humidity at home is as easy as cooking an extra meal a day. Mainly, stovetop cooking releases moisture into the air. It doesn’t have to be a five-star meal, simply boiling pasta or potatoes will do.

Invest in Houseplants

Plants continuously emit moisture from the leaves as vapor (9). We call this the process of transpiration. It will continue to occur as long as you keep watering them, as needed, of course.

High Indoor Humidity

Problems Associated With High Humidity Levels

High humidity is common during summer, but it can occur in any season or when you overuse a humidifier. It’s essential to watch out for this as it can lead to significant damage to the home.

Effects of High Humidity on Health

Although high humidity can have direct effects on health, the impact it has on the home can also result in ailments:

  • Excessive sweating, overheating, and heat stroke.
  • Increased occurrences of asthma and allergy flare-ups (10).

High Humidity Effects on the Home

The home is where you’ll see a direct impact of the increased humidity. This includes:

  • Excessive condensation on windows.
  • Wet spots and stains on ceilings and walls.
  • Mold in high-moisture areas, including the bathroom.
  • Musty smells.
  • Mildew growth.
  • House structure may begin to rot.
  • Increased chance of pests.

How to Lower Humidity

Use a Dehumidifier

Dehumidifiers are the opposite of humidifiers — instead of restoring moisture, they remove it.

If moisture worries you, it’s good to invest in a portable dehumidifier so you can place it where needed.

For those with a larger budget, consider a whole-house dehumidifier if excessive humidity is a recurring issue.

Use Exhaust Fans

Exhaust fans generally sit in the kitchen and bathroom, venting out odors and humidity. Try to run the fan each time you cook and after showers.

Take Cold Showers

Taking a cold shower isn’t what most of us want to hear. And yes, in the winter, we’ll leave them to the Vikings.

Still, following a hot shower, all the steam and humidity left in the air can cause trouble if not properly vented. This is why it’s a good idea to take the heat down when you can.

Run Your AC

Air conditioners are fantastic at lowering indoor humidity. As they draw air in from outside, they filter out the moisture inside. However, ensure that you keep the filters clean; otherwise, they prevent the filtering process.

Avoid Boiling Water

When the indoor humidity is higher than usual, avoid boiling water, such as when cooking pasta or potatoes. The condensation of the water can increase the humidity significantly. If you must, make sure you vent out the vapor properly.

Prevention

If your house has a crawl space with an exposed dirt floor, use a polyethylene ground cover to seal it (11). Ensure the dirt is dry and that there’s no standing water. If moisture is present, use a fan to dry it.

Next, have a look at your dryer. Make sure the vents lead outside and not indoors, as this will cause high humidity.

FAQs

What Causes High Indoor Humidity?

Several things cause high indoor humidity, including poor ventilation, a lack of insulation, running too many appliances, drying clothes indoors, and stovetop cooking. Humans and pets also increase humidity when they breathe and sweat.

What is the Best Humidity Level for Sleeping?

The best humidity level for sleeping is between 30 and 50 percent. Air below 30 percent is too dry, and above 50 percent is too wet.

What Should the Humidity Be In a House With Air Conditioning?

The humidity in your house should be 30 to 50 percent, even with air conditioning. Keeping the moisture levels between these two points is crucial for a comfortable indoor environment and for health reasons.

What Humidity Does Mold Grow At?

Humidity above 55 percent helps mold grow, which is why experts recommend keeping your indoor moisture levels to between 30 and 50 percent.

How Long Does It Take to Humidify a Room?

It takes between three and twenty-four hours to humidify a room. Several factors affect your success rates, like room dimensions, humidifier capacity, and existing moisture levels.


To Humidify or Dehumidify?

The ideal indoor humidity is anywhere between 30 to 50 percent (12). This does differ from summer to winter, so using a hygrometer or other tools to check is essential.

Indoor humidity that is too high or too low can have adverse effects. High levels lead to mold and mildew, whereas low moisture creates a good environment for bacteria and viruses. Both are capable of making us sick.

The best ways to combat low humidity are by running a humidifier where needed, cooking more and air-drying laundry. To avoid high humidity, run a dehumidifier and vent out vapors that result from cooking and showering.

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About the Author

Matthew Sullivan

Matthew Sullivan is a technical writer with over 15 years of hands-on experience in the realm of HVAC, humidity, air purification, and mold prevention. With a background rooted in mechanical engineering, Matthew seamlessly blends the intricate world of technicalities with the everyday challenges that homeowners and businesses face. His vast expertise has led him to collaborate with leading HVAC manufacturers, consult on cutting-edge air purification systems, and become a sought-after voice on mold mitigation.