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Relative Humidity: What Is It and What’s the Right Level for Your Home?

If you suffer from chronic respiratory conditions, such as asthma, chronic obstructive pulmonary disease (COPD), or allergies, there’s no doubt that you’ve noticed when heat and humidity levels are high, your symptoms flare up. That’s because heat and humidity can lead to an increase in air pollutants, such as bacteria, dust mites, and mold spores, irritants that can aggravate your lungs. However, low humidity levels can impact your health too, as repetitive exposure to dry air can irritate the eyes, nose, and throat. Physical health isn’t the only thing that is directly impacted by your humidity. When moisture levels in the air is too high or too low, your home can sustain structural damage.

Fortunately, there is a way that you can manage and maintain indoor humidity. How? With a humidifier or a dehumidifier. These appliances can help you achieve ideal humidity levels and have been proven to prevent the exacerbation of respiratory health conditions and structural damage. When attempting to manage indoor humidity levels, it’s important to understand what it is and how it works so that you can properly maintain it, and the first thing to understand is that the term “humidity” is used, typically, it describes relative humidity and not absolute humidity.

What’s the difference between relative and absolute humidity? Why is it important to know the difference? What is the ideal relative humidity level? To find the answers to these questions and more, keep on reading.

Relative Humidity Explained

Humidity refers to the amount of water vapor or moisture in the air, and that moisture depends on the temperature of the air. Relative humidity refers to the amount of moisture in the air at a specific temperature in comparison to the amount of humidity the air can effectively hold at that particular temperature. With that said, however, it’s important to know that air itself cannot actually hold onto water vapor, as it’s constantly moving and moves too fast. When indoor air reaches particular capacity of water vapor, it condenses into moisture. When the percentage of water vapor in the air is high, the air is considered humid and it feels damp, and when the percentage is low, the air feels dry.

The amount of relative humidity that is present in your home’s indoor air depends on the climate you live in. Obviously, if you live in a tropical climate, the humidity levels in your home will be high, and if you live in a region where the climate is arid (dry), the humidity in your home will be low. When trying to determine how to improve the comfort and health of the air inside your home, relative humidity needs to be taken into consideration. Relative humidity enables you to understand how much moisture is present in the air, and thus, you can then determine how to improve the levels; whether you should use a dehumidifier or a humidifier, for example.

Like water vapor, relative humidity is expressed in terms of pressure or density and is expressed as a percentage. It can be calculated by dividing the actual vapor pressure (gram-per-cubic –meter or g/m3) by saturation vapor pressure (gram-per-cubic-meter or g/m3) – or the actual vapor density by saturation vapor density – and then multiplying the quotient of the equation by 100 in order to get a percentage, and that percentage is the relative humidity. In order to calculate the relative humidity of your home’s indoor air, you can use a hygrometer and a dehumidifier.

The Difference Between Absolute Humidity and Relative Humidity Explained

Absolute humidity refers to the actual amount of moisture in the air. It can be explained mathematically as a measure of the amount of water vapor (g/m3) in the air, no matter the temperature. The higher the level of water vapor in the air, the higher the absolute humidity will be. When the air feels really damp, that dampness you feel is absolute humidity.

When measured, relative humidity is a percentage or a ratio of the amount of water vapor in a volume of air that is relative to a specific temperature and the amount of moisture the air can hold at that specific temperature. The warmer the air, the more moisture it can hold, and the colder the air, the less moisture it can hold. In other words, the relative humidity level can be higher in cold air and lower in warm air at the same absolute humidity level. While relative humidity and absolute humidity might seem like the same thing, they are different and are not interchangeable.

Why Relative Humidity Matters

Relative humidity is important because it has a direct impact on the comfort and safety of your home. When relative humidity levels are greater than 50 percent, the air inside your home will feel damp, and that dampness creates the ideal environment for trapping of allergens and the growth of fungus, like mold and mildew, and bacteria. Exposure to these elements can exacerbate existing respiratory health conditions, such as asthma, COPD, and allergies; it can also lead to the development of new respiratory health conditions. In addition to health issues, the humidity levels in your home’s indoor air can potentially damage building materials and compromise the structural integrity of your home. Mold growth, for example, can weaken the fibrous materials that your home is constructed of; sheetrock, insulation, wood, etc.

When you understand relative humidity, you can properly examine the exact amount of moisture that is present in the air at any point in time. You can use that information to determine how much humidity is present in your home and thus, whether you need a humidifier or a dehumidifier.  

Understanding Healthy Indoor Air

Like most people, you probably spend a great deal of time indoors; it is estimated that the average person spends about 90 percent of their time inside. You might be surprised to find, however, that the environment where you spend the majority of your time may not be the healthiest – particularly in regard to the air. According to numerous studies, the level of indoor air pollutants can be up to five times greater than the level pollutants in outdoor air.

Though you might be able to see some of the pollutants that are circulating through your home’s indoor air – accumulated dust on furniture and pet hair on floors, for example – you can’t see everything that’s contaminating your home’s indoor air. In fact, you can’t see the majority of the pollutants that circulate through and negatively impact your home’s indoor air. Some of the most common sources of indoor air pollutants include:

  • Asbestos fibers and particles
  • Bacteria
  • Carbon monoxide
  • Chemicals, such as those found in cleaning supplies and the off-gassing of chemicals, like formaldehyde, used on furnishings, such as carpeting and rugs
  • Dust and dust mites
  • Lead
  • Mold and mildew spores
  • Volatile organic compounds (VOCs); chemicals that contain carbon and that readily evaporate at room temperature and turn into gas

If any of these contaminants are present in your home, your indoor air really needs to be cleaned. But what makes indoor air clean? Clean indoor air can be described as:

  • The relative humidity is 50 percent or less
  • Free of toxins
  • Properly ventilated
  • Fresh-smelling

Understanding Household Humidity

So, how does moisture enter – and get trapped in – your home. There are several ways. Firstly, if you live in a tropical climate that receives a lot of rain and where outdoor heat and humidity levels are high, it stands to reason that the moisture content inside your home is going to be higher than it would be if you were to live in a climate that is arid and receives little rain. That’s because outdoor air – and the moisture it contains –travels indoors through, and the moisture can get trapped.

The climate you live in isn’t the only thing that will affect the humidity levels inside your home. Indoor water use will, too. For example, spaces where water is used regularly, such as bathrooms, the kitchen, and the laundry room, tend to be more humid than space where water isn’t used, such as the bedrooms, living room, and dining room. Additionally, rooms where ventilation is poor are more humid than those that are properly ventilated; for example, spaces that lack windows or lack ventilation fans have higher relative humidity content than those that have windows and ventilation fans.

Some of the most common causes of high relative humidity levels indoors include:

  • Roof leaks
  • Leaking pipes and plumbing fixtures, such as toilets, sinks, washing machines, dishwashers, and even refrigerators and freezers
  • Improper or ineffective rainwater runoff; clogged gutters, for examples
  • Steam caused by cooking without proper ventilation
  • Bathing in poorly ventilated bathrooms

What is the Ideal Indoor Relative Humidity Level?

Relative humidity levels that are above 50 percent are considered too high. With that said, however, it’s important to understand that while you don’t want the relative humidity level inside your house to be too high, you also don’t want it to be too low. Generally, humidity levels that fall below 30 percent are considered too low. As such, the ideal indoor relative humidity level falls between 30 percent and 50 percent; in fact, that range is recommended by the US Environmental Protection Agency (EPA). It should be noted, however, that ideal level for your home depends on the climate that you live in, as well as your own personal preference.

The Impact of High Relative Humidity Levels Inside Your Home

As the temperature increases and decreases, the air’s ability to hold water changes. The warmer the air is, the more moisture it can hold, and the cooler the air is, the less moisture it can hold. Excessive relative humidity levels can cause a number of problems; most notably, it can negatively impact the indoor air quality of your home, which can not only be detrimental to your physical health, but can also be detrimental to the structural integrity of your house.

Whether the result of the climate you live (a tropical climate, for instance) or because of poor ventilation, leaking pipes, etc., high relative humidity levels can have several  negative implications on your home and your health.

Effects on Your Home

  • Dampness
  • Mold and mildew growth
  • Musty odors
  • Peeling wallpaper
  • Bubbling paint
  • Warped wood, such as floors and furniture
  • Electronic equipment malfunctions
  • Condensation and/or fog on windows and mirrors
  • Water stains on ceilings, walls, and furniture
  • Sticking doors and windows due to swollen wood

Effects on Health

  • Exacerbation of existing respiratory conditions, such as asthma, COPD, and allergy symptoms
  • Development of new respiratory conditions
  • Skin irritations, such as rashes, as the pores can become clogged and unable to release sweat
  • Irritation of the eyes, nose, and throat
  • Increased risk of certain types of cancers and nervous system damage, due to increased off-gassing of volatile organic compounds (VOCs)
  • Persistent fatigue
  • Irritability and mood changes
  • Persistent headaches
  • General malaise

The Impact of Low Relative Humidity Levels in Your Home

As noted, low relative humidity levels aren’t ideal, either; anything less than 30 percent is considered too low. If you live in an arid climate that receives little rainfall or you use forced heating or a wood or coal-burning fireplace on a regular basis, the relative humidity levels inside your home can fall to low levels. Like high relative humidity levels, low relative humidity levels can have implications on your home and your health.

Effects on Your Home

  • Peeling wallpaper and paint
  • Wood shrinkage, such as floors, around windows and doors, and even furniture
  • The development of gaps between the walls, ceilings, and floors

Effects on Your Health

  • Increased risk of respiratory illnesses and the common cold
  • Exacerbation of existing respiratory conditions, such as asthma, COPD, and allergies
  • Dry skin, hair, and lips
  • Dry, irritated, and scratch eyes, nose, and throat
  • Regular static electricity
  • Repeat bloody noses

How to Maintain an Ideal Relative Humidity Level in Your Home

To maintain an ideal humidity level in your home – between 30 and 50 percent – you might want to consider investing in a dehumidifier or a humidifier.

A dehumidifier is an appliance that removes excessive moisture from indoor air, thereby reducing the relative humidity level. They pull moisture out of the air, which makes it less hospitable to molds, mildew, dust and dust mites, and other allergens, as well as viruses and bacteria. You can purchase portable dehumidifiers or if you have an HVAC system, you can have a whole-house dehumidifier installed right into the system.

A humidifier is an appliance that increases the relative humidity level of indoor air. They emit water vapor into the air, which will help to make a dry indoor environment healthier and more comfortable. There are both warm and cool mist humidifiers. Like a dehumidifier, you can purchase a portable humidifier, or you can have a whole-house humidifier installed into an HVAC system.

Schedule An Appointment with a Mold Testing Professional

If the relative humidity level in your home is 50 percent or higher, you should seriously consider scheduling an appointment with a professional mold assessment company. Mold needs moisture to thrive, and therefore, if your indoor air is humid, there is a very good chance that mold could be growing within your house, completely unbeknownst to you.

Exposure to mold can cause serious damage to your house, and worse, it can cause serious health complications. As mold spreads, it feeds on the surface it grows on, and eventually, the structure integrity of your house could eventually be compromised. Breathing in mold spores can aggravate existing or lead to the development of new respiratory health conditions. It can also cause allergies, irritation to the skin, eyes, nose, and throat, lethargy, chronic headaches, mood changes and irritability, cognitive issues, and general malaise.

In order to prevent the devastating effects that mold growth can cause to both your home and your health, having a professional perform a mold inspection is highly recommended. At Mold Inspection and Testing (MIT), a leading mold assessment and testing company, we use the most state-of-the-art tools, equipment, and technologies to perform the most comprehensive mold inspections. Our professionally trained technicians will be able to determine whether or not mold is growing inside your home and if so, the severity of the problem. You can then make arrangements to eliminate the mold and improve the overall health and safety of your home.