Ideal Indoor Humidity Chart

High indoor humidity is a common problem for homeowners, especially in humid climates. The ideal indoor humidity levels range from 30% to 50% RH. Anything below this is considered too low and can dry up your skin, eyes, and airways. On the other hand, too much moisture in the environment encourages the the growth of mold, mildew, dust mites, and other pests or harmful microorganisms. 

With high humidity, these airborne particles can trigger allergy symptoms, asthma attacks, and other respiratory issues. Excess humidity can also damage furniture and your house structure over time. There are many ways to improve indoor air quality, and control humidity and prevent its harmful effects, but perhaps the most effective and efficient solution is by using a dehumidifier. 

When setting the humidity level on your dehumidifier,you must also take note of the ambient temperature. Usually, the most comfortable indoor humidity level for people is around 45% RH, but if the outside temperature is too cold, you can set the humidity level lower. Keep reading to learn more about the ideal relative humidity levels indoors.

What is Humidity?

Control Humidity

First, you must understand exactly what humidity means. Where there’s water and heat, the air will contain some amount of water vapor. This is what we call humidity. The relative humidity percentage that we measure is the actual amount of water present 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 reaches 100% relative humidity or when it cannot take in more water vapor.

While the temperature does not directly change the relative humidity (and vice versa), one has some impact on how we perceive the other. In particular, as the temperature increases, the air can hold more water molecules, allowing more moisture to evaporate. If the moisture remains in the air, this leads to higher relative humidity.

Conversely, when humidity levels are high, hot temperature feels even hotter and uncomfortable  because it’s too saturated with moisture. Meanwhile, when the air is too cold, it can hold fewer water molecules. If the temperature drops but the humidity remains the same, it becomes too cold and damp. Neither situation is good for your health or for your house. To maintain utmost comfort in your home, it’s important to control the humidity based on the ambient temperature.

What is the Ideal Indoor Humidity and Temperature

What is the Ideal Indoor Humidity and Temperature

The ideal indoor humidity level is from 30% to 50% RH. When it drops below 30%, this is often considered too low for your comfort. Dry air readily absorbs water from any moist surface, including your skin, eyes, and airways. When the humidity is too low, you may experience dry, itchy eyes, scratchy throat, and nasal congestion. 

On the other hand, humidity levels above 50% can create an environment suitable for the growth of mold and mildew, and other microorganisms which can then lead to health problems and eventually damage different materials in your home. 

The ambient temperature also affects your comfort levels within the range of ideal indoor humidity. The lower the temperature, the less water vapor the air can hold. Thus, you may be more comfortable at a lower humidity level during colder days.

If the outdoor temperature is above 40°F, you can set the relative humidity at 45%. If the outdoor temperature is between 20°F and 40°F, the ideal humidity is 40%. If the outdoor temperature is between 10°F and 20°F, the ideal humidity is 35%. And if the temperature is below 10°F, the ideal humidity is 30%. Use the chart below for easier reference.

Ideal Indoor Humidity Chart

Outdoor TemperatureRecommended Relative Humidity
> 40°F45%
20–40°F40%
10–20°F35%
0–10°F30%

When using a dehumidifier, it’s not always best to select the lowest humidity level available on the unit. Note that most dehumidifiers will only work in temperatures down to 41°F or 33°F depending on the type. 

How Does a Dehumidifier Work?

A dehumidifier lowers humidity and removes moisture from the air using different methods. The two main types of dehumidifiers are called refrigerant and desiccant. Each type offers different options for humidity control. 

Refrigerant

The refrigerant dehumidifier is the most common type of dehumidifier used at home. It works similarly to an air conditioner and other cooling appliances with a refrigerant system. It uses a compressor to pump the refrigerant to and from the coils to initiate condensation of the excess moisture in the air. 

First, the warm, moist air is drawn in by a fan and then passes through the cold coils. The water vapor condenses as the air temperature decreases. It forms water that drips into a reservoir at the bottom. The dryer air is then released into the room at a slightly warmer temperature. Refrigerant dehumidifiers today can remove a total of 20 to 50 pints of moisture per day. 

Most refrigerant dehumidifiers include a humidistat that allows you to set the relative humidity from 30% to 80% or 90%. The dehumidifier pauses periodically to measure the humidity in the room and automatically resumes operation to maintain your preferred setting. If your dehumidifier has this feature, set the humidity between 30% and 50% based on the temperature. 

How Dehumidifiers Work Air Flow

Desiccant

A desiccant dehumidifier uses some kind of hygroscopic chemical or desiccant that extracts moisture in the air until the desiccant’s maximum capacity is reached. It can be either disposable or renewable depending on the desiccant used. Some desiccants (such as salt crystals like potassium chloride) dissolve into a liquid as they absorb moisture and must be disposed of after one use. Silica gel, for example, is a renewable desiccant that can be recharged simply by heating to dry out the moisture. 

Full-sized residential desiccant dehumidifier also use silica gel inside a wheel. Unlike other desiccant types, it includes a heater and a condenser. After drying the air by passing through the desiccant, a small portion is turned around and heated. This warm air absorbs the moisture from the saturated desiccant then condenses it into water. Although typically smaller than even the smallest refrigerant dehumidifiers, this desiccant unit also includes a humidistat. It has the advantage of working at even lower temperatures. 

Peltier

Another type of mini dehumidifier uses the Peltier effect or thermoelectric cooling technology. The main process is similar to that of a refrigerant dehumidifier but on a much smaller scale. Instead of a compressor and metal coils, this mini dehumidifier is composed of a Peltier module and a heat sink on each side. 

As the air cools down on the cold side of the Peltier, vapor condenses and drips into the tank. The dry air now passes over the hot side before it is released into the room. The capacity of Peltier dehumidifiers typically range from 8 to 16 ounces a day or up to 30 ounces for the largest units.

Peltier or thermoelectric dehumidifiers are perfect for small rooms and mobile homes due to the quiet operation and low energy consumption. However, they don’t provide precise control over the humidity levels. They usually only include one button for the power switch. There is no way of knowing and adjusting the exact humidity level.

What are the Effects of Low Humidity?

With low humidity, the dry air will absorb moisture from any moist surface including your skin, eyes, and nasal airways. Dry air can irritate your nasal passages and lead to congestion or a scratchy throat. It can also cause flaking and cracking of dry skin due to scratching. 

Dry air also makes tears evaporate fast, causing dry, itchy eyes, and in worse cases, even blurred vision. Additionally, some disease-causing bacteria thrive in low humidity and spread easily in this type of dry environment. This is why allergies and cold or flu symptoms are common during winter.

Over time, low humidity can also cause drying and cracking of wood beams and other wooden materials like furniture and musical instruments. Wood is particularly sensitive to humidity and easily loses moisture to the dry air and shrinks in size. In contrast, wood absorbs moisture and expands when exposed to high levels of moisture.

What are the Effects of High Humidity?

A common sign of humidity is a musty odor. The air may also feel heavy or sticky because it is already saturated with moisture and can’t absorb perspiration. Humid air is difficult to breathe since it contains high amounts of water vapor and fewer oxygen molecules.

High humidity creates a perfect environment for common allergens such as mold and dust mites. Touching mold or inhaling mold spores may trigger allergies and asthma attacks. Dust mites also thrive in high humidity and leave waste products that can trigger allergic reactions such as sneezing, runny nose, and eye irritations.

Mold and mildew can grow on walls, ceilings, furniture, particularly in moist surfaces. They feed on organic material like wood and soft furnishings, causing damage to furniture and your house structure. Dark-colored molds are common in the bathroom or along wall corners.

Damp spots on walls, ceilings, and floors can also be caused by high humidity. This can lead to cracks in the drywall and gaps between the floor and baseboard. Excess moisture can also lead to rusting metals, rotting wood, and termite infestation. 

Summary

Controlling both the temperature and humidity allows you to achieve the most comfortable indoor environment. The recommended relative humidity range is from 30% to 50%, but the best setting for your home at a particular time also depends on the temperature outside. When it’s colder, you may need to set the humidity level a little lower to remain comfortable. 

Be mindful in using the right appliance to help achieve the ideal indoor humidity in your home. It helps to have a hygrometer to measure indoor humidity. When relative humidity reaches 60% and higher, this is the time to use a dehumidifier. Using your dehumidifier when humidity is already low, you may suffer from the harmful effects of dry air on your health and surrounding.

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