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by Catherine Poslusny

When you think about the air quality in your home, you’re probably more focused on indoor air pollution than moisture content. However, the amount of water in the air, also known as relative humidity, can impact your health and home just as much (or more) than many types of air pollution. There’s a sweet spot for proper home humidity levels, and when the air in your home gets above or below that range, it may be time to consider getting a humidifier or dehumidifier.

Relative humidity refers to the amount of water in the air relative to how much the air can “hold” at a specific temperature. The Environmental Protection Agency (EPA) recommends an ideal humidity between 30 and 50% to avoid the effects of air that is too humid or too dry.

Here, we break down why you should care about relative humidity, how to raise or lower home humidity levels, and what to do when you need a humidifier or dehumidifier.

Hygrometer showing humidity levels

How to measure humidity in your home

The easiest way to detect a humidity problem is to use a hygrometer. This little device typically looks like a thermometer, and it measures the moisture levels in the air. You can find them online or in most hardware stores. If your relative humidity measurements are consistently above 50 to 60%, your home is probably too humid. If you don’t have a hygrometer, don’t worry. There are still plenty of clues you can use to spot an excess humidity issue in your home.

How does excess humidity affect your home?

Excess indoor humidity levels are most common in warm, humid climates and during the summertime, as air can hold more moisture as it gets warmer. When your home is too humid, the excess moisture can start to impact your structure, belongings, and indoor air quality. It can also create the perfect environment for biological pollutants (such as mold and dust mites) to grow and thrive and attract certain pests, including roaches, mosquitos, and termites.

Mold growing in the corner of a home

Signs of high humidity in homes include:

  • Visible mold, especially in the corners of your closets, bathrooms, or kitchen;
  • Musty odors;
  • Bathroom mildew;
  • Cracking, peeling, or bubbling paint;
  • Peeling or bubbling wallpaper;
  • Condensation on windows, walls, or other cool surfaces;
  • Warped or rotting wood in floors or furniture;
  • Windows or doors starting to stick;
  • Water stains on ceilings.

How can excess relative humidity affect your health?

Damp, musty environments can encourage the growth of bacteria, dust mites, and molds. This can mean increased symptom flare-ups for people with asthma and allergies. Even in otherwise healthy individuals, mold exposure may cause coughing, wheezing, and other respiratory issues. Those with allergies, lung disease, compromised immune systems, or other respiratory conditions may be vulnerable to more severe health effects.

Potential health effects of excess humidity and increased allergen exposure include:

  • Runny nose;
  • Itchy, red, or watery eyes;
  • Sneezing;
  • Coughing and congestion;
  • Facial pain caused by sinus pressure;
  • Skin rash;
  • More frequent asthma attacks;
  • Itching in the nose, throat, or mouth;
  • Difficulty breathing;
  • Chest pain or tightness;
  • Trouble sleeping due to respiratory issues.

Large crack spreading through the interior wall of a house

How can you tell if your home is too dry?

Dry air is most common during the winter, as cold air cannot retain moisture as well as warmer air. Plus, cooler indoor temperatures often lead to increased use of fireplaces and heaters, which can dry out your indoor air even further. If you live in an older home with cracks or gaps around the windows and doors, you may be more likely to notice the effects of dry air caused by cold outdoor temperatures. Aside from using a hygrometer to detect low relative humidity—anything below 30%—you can also keep an eye out for signs of dry air in your home.

How can dry air affect your home?

When the relative humidity in your home is too low, the air can start to draw moisture from other places, such as floorboards and walls. Just as wood and other materials can absorb excess moisture when humidity is too high, they can also lose moisture when it is too low. Effects of dry indoor air include:

  • Cracks and warping in wooden furniture and fixtures;
  • Separation and cracks in wooden floorboards;
  • Cracks in leather furniture;
  • Peeling or bubbling wallpaper;
  • Peeling, cracking, or bubbling paint;
  • Gaps between the ceiling and walls;
  • Warping in windows and door frames;
  • Damage to books, musical instruments, and art.

Dry air can also cause static electricity to build up, which is why many people notice increased static cling and shocks during the cold winter months. Increased static electricity also makes it easier for dust to cling to the surfaces in your home, and it may occasionally interfere with the functioning of electronics.

How can dry air affect your health?

While excess relative humidity primarily causes indirect health effects—due to the increased presence of mold, dust mites, and other biological pollutants—dry air can have a more direct impact on human health.

Your respiratory tract needs moisture to function properly. The mucus that lines your sinuses keeps your respiratory tract hydrated and catches viruses, bacteria, and other pollutants before they enter your body. However, it needs to be moist to do its job. When dry air causes your mucus to dry up, it leads to respiratory discomfort and leaves you more vulnerable to viruses and infections.

Symptoms and effects of dry indoor air can include:

  • Dehydration;
  • Dry, chapped, or cracked lips;
  • Itchy, dry, or flaky skin;
  • Dry hair;
  • Nosebleeds;
  • Dry, irritated, or sore eyes, nose, and throat;
  • Respiratory problems, such as bronchitis and sinusitis;
  • Worsened cold and flu symptoms;
  • Worsened allergy and asthma symptoms.

Dehumidifier in a room with moldy walls

How to dehumidify a house

The first step in dehumidifying your home is determining where the excess moisture is coming from. First, find and fix any leaky pipes or places where water is entering your home from the outdoors. Next, use exhaust fans, ventilation, and dehumidifiers to lower the relative humidity in your home.

It is normal for different activities to temporarily raise your indoor humidity, such as warm showers, boiling water, and air-drying clothes. When the excess moisture doesn’t dissipate on its own, it’s your job to help dry out the air in your home. Exhaust fans work by pulling out humid indoor air and venting it outside (as long as your vents lead outdoors and not to the attic). They’re especially useful in high-moisture areas, such as bathrooms, kitchens, laundry rooms, and rooms with potted plants.

Your heating, ventilation, and air conditioning (HVAC) system can also help circulate the air in your home and remove moisture. Make sure to change air filters regularly and clean ducts as needed to keep your HVAC system from blowing mold, dust, or other pollutants into your home.

Though HVAC systems, exhaust fans, and even open windows (on non-humid days) can help lower the moisture levels in your home, they may not be enough to reduce relative humidity to healthy levels. In that case, a dehumidifier can help you get the job done.

How to choose a dehumidifier

Dehumidifiers work by cooling the air that passes through the unit, decreasing its ability to hold moisture. The liquid pulled from the air then collects as condensation on the cooling coils and drips down into a drain pan or bucket. To get the most use out of your dehumidifier, put it in the room with the highest relative moisture. If your whole home has a moisture problem, you may need more than one dehumidifier.

When shopping for a dehumidifier to rent or buy, you’ll notice two primary units in the product description: square feet and pints. “Square feet” refers to the size of the room in which you’ll be using the dehumidifier. “Pints” refers to the unit’s capacity, or how much water it can pull out of the air over 24 hours. Don’t worry if you’re not sure how much water is actually in your indoor air. These Energy Star guidelines can help you get an idea of what kind of dehumidifier you should choose for your home:

For a “moderately damp” room that only feels damp or musty during humid weather:

  • 500 sq. ft.: 10-pint dehumidifier
  • 1,500 sq. ft.: 18-pint dehumidifier
  • 2,500 sq. ft.: 26-pint dehumidifier

For a “very damp” room that always feels musty and has damp spots on the ceilings or walls:

  • 500 sq. ft.: 12-pint dehumidifier
  • 1,500 sq. ft.: 22-pint dehumidifier
  • 2,500 sq. ft.: 32-pint dehumidifier

To lower humidity in small, enclosed areas, such as crawl spaces or cabinets, you can use a desiccant. Desiccants are a sort of “low-tech” dehumidifier that have no moving parts and don’t use electricity. For example, the little silica gel packets you see at the bottom of many boxed products are desiccants that prevent mold and moisture buildup during shipping. You can find desiccants for home use, sometimes called moisture absorbers, online and in hardware stores.

Small humidifier on a side table near a modern couch

How to add humidity to a house

Combating dry air requires two steps: adding moisture to your indoor air and sealing your home to prevent the moisture from leaving. The latter can be accomplished by using weatherstripping or caulking to fix any gaps or cracks in your walls, windows, or door frames. As a bonus, sealing your home can also help it retain heat, reducing the need for fireplaces or heaters that can make dry air even worse.

There are a few ways to add moisture to the air in your home. Most are only temporary, such as taking a hot shower or boiling water on the stove. Watering your houseplants can also increase your indoor humidity. Be careful not to overwater, though. Wet soil can start to grow mold, even when the relative humidity in your home is low. For more consistent help with dry air, you can use a humidifier.

How to choose a humidifier

Humidifiers release water vapor into the air, raising the relative humidity in the surrounding area. Like dehumidifiers, they are rated for specific room sizes, so you should keep that in mind when choosing one for your home. You’ll also need to decide whether you want a warm mist or cool mist humidifier. Warm mist humidifiers work by boiling water and releasing steam into the room. Cool mist humidifiers use wicks or moving parts to help water evaporate from a tank and add moisture to the air.

The choice between cool and warm mist humidifiers depends mostly on personal preference. However, if you have pets or small children that may knock over the unit, a cool mist humidifier may be a better option. Since there is no heating element, spills don’t pose any danger of burns or scalding.

To get the most benefit from your humidifier, try to use it in the room or rooms where you and your household spend the most time. Additionally, you can maximize your humidifier’s effectiveness by:

  • Placing it on a table, nightstand, or other raised surface a few feet off the ground;
  • Using it in the room size recommended by the manufacturer;
  • Keeping it unobstructed by walls, furniture, or ceilings;
  • Placing it somewhere it’s not likely to get kicked or knocked over.

When adding moisture to your home, there is a slight risk of increased mold growth. You can help prevent this by cleaning your humidifier regularly. If you notice condensation or extra moisture around the unit, it may be a sign you need to run it less frequently or move it farther away from surrounding objects.

So, do you need a humidifier or dehumidifier?

In short, high humidity over about 50% requires a dehumidifier, and low humidity under about 30% requires a humidifier. Spending too long outside the ideal humidity range could lead to discomfort, health effects, and structural and cosmetic problems in your home. Fortunately, there’s an easy fix for minor humidity issues—humidifiers and dehumidifiers. Some units even have a built-in hydrometer that turns the power on or off depending on the relative humidity in the room. Both humidifiers and dehumidifiers are available at a wide range of prices and features. So, with a bit of research, you should have no problem finding the right one for your specific situation.

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