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The Ideal Indoor Humidity Level to Maintain


Y ou likely spend most of your time indoors, so creating proper conditions health- and comfort-wise is essential for life quality. While people mostly tend to focus on temperature, creating a cooler environment during summer and seeking warmth during winter, one aspect that is woefully overlooked and has a major impact on environmental conditions is humidity.

Regardless if we are discussing dry or damp air, it’s important for both scenarios to be avoided as not only can your health suffer as a result, but so will your home when it comes to structural integrity. Needless to say, there are methods to upkeep relative humidity within proper parameters, and here, we will provide you with info related to what level you must aim to maintain, as well as offer you suggestions when it comes to what you must do to reach the goal.

What Is Humidity?

Definition: It represents the amount of vapor existent in the air. What is referred to as relative humidity or RH is the proportion of water vapor currently in the air in relation to the quantity of water the air can actually hold.

Relative humidity actually fluctuates according to temperature, so when the temperature rises or drops, the air’s aptitude to hold water changes as well, impacting comfort levels in turn. As we will explain in detail in the following, high and low RH levels impact air quality, so this is an environmental condition factor that you must keep track of at all times.

At What Level Should Indoor RH Be Maintained?

There are two answer versions to this question – the EPA advises that you upkeep indoor RH from 30% to 50%, while scientists recommend indoor humidity be kept within 40% to 60%. Regardless of what guidelines you opt to follow, whether it is the recommendation of the EPA or that of scientists, know from the get-go that you are in the clear from health and environmental repercussions as long as humidity doesn’t drop below 30% or raises above 60%.

To handle health effects and illness regardless of season or other factors, the American Society of Heating, Refrigeration, and Air Conditioning Engineers encourages to keep RH levels within 45% to 55%. Use an indoor hygrometer to check if humidity drops or raises beyond these parameters so that you know what course of action you should take to return everything back to normal.

Evidently, your personal preference factors in as well. Some individuals feel better when RH indoors is at 40%-45%, whereas others feel better at a slightly higher level. However, as long as you stay within the aforementioned parameters, you won’t suffer any consequences. To upkeep proper comfort levels, you can use the following as guidance. Here, we will provide you with a temperature to moistness correlation guide that you can use to establish environmental comfort more easily:

  • Outdoor temperature exceeds 50°F: Maintain indoor RH below 50%;
  • Outdoor temperature exceeds 20°F: Maintain indoor RH below 40%;
  • Outdoor temperature from 10°F to 20°F: Maintain indoor RH below 35%;
  • Outdoor temperature from 0°F to 10°F: Maintain indoor RH at 30%.

Problems Caused by Improper RH Levels

Throughout the year, as temperatures shift and change, so do RH levels indoors. Evidently, not only the weather impacts indoor humidity as day-to-day activities take a toll on environmental conditions as well. Nonetheless, what is a given is that, as aforementioned, high and low RH impacts life quality and even building structure, so it’s essential that you maintain the level within recommended parameters to not feel the repercussions.

Low Indoor RH Issues

During winter and generally, when the weather becomes cold, the air isn’t able to hold as much water anymore, for this reason, RH dropping amidst the cold season.

Fixing low humidity is a must for your health and home as the following problems arise if you ignore the problem:

  • Amplification of asthma and allergy symptoms;
  • The rapid spreading of cold and flu viruses;
  • Increased chances of sinus infections and congestion;
  • Dry skin and air passageways;
  • Affects the way you feel warmth, even if you turn heating appliances on making the environment feel colder than it is;
  • Flooring, wood furniture, and building materials can crack and damage as moisture is pulled from them.

High Indoor RH Issues

During summer and generally, when the weather is hot, the air can retain a lot more moisture, which leads to RH levels amplifying considerable amidst the warm season.

Fixing high humidity is an issue you must urgently tend to as its repercussions can include:

  • Provides growing grounds for mold, bacteria, fungi, mildew, and viruses;
  • Frequent and worsened symptoms in asthma and allergy sufferers;
  • Condensation forms on windows and walls;
  • Damp air ultimately causes you to need to turn up the AC as the environment will feel hotter, leading to discomfort;
  • Building structure can be weakened if moisture levels rise too much and aren’t lowered as needed in time.

Controlling RH Levels Throughout the Year

As previously stated, both the cold and hot seasons take a toll of indoor humidity, each in their own way. When summer comes, expect for the air to be damper than recommended, whereas in winter it won’t be able to hold much moisture so it will become dry, predisposing you to respiratory infections, among other issues.

As you likely deducted by now, both dry and moist air impact symptoms in allergy and asthma sufferers, so even if you manage to keep humidity in check, use an air purification system that targets symptom-triggering particles to make sure that even when RH fluctuates, your health problems won’t act up.

How to Solve Low RH

When RH drops below 30% and dryness starts to become problematic, potentially causing dry and itchy skin, predisposition to colds and infection, and ruin of wood floors and furnishings, among other problems, you can proceed as follows to normalize humidity in the air:

  • Install a furnace humidifier that raises moistness throughout the entire house or use a portable humidifier if RH levels need fixing only in some areas of the house.
  • You can place water basins in the proximity of the heating system so that the water evaporates and adds moistness into the air.
  • Add houseplants as they not only help stabilize dampness levels but help purify the air of certain airborne pollutants as well, including the likes of benzene and formaldehyde.

How to Solve High RH

When RH raises above 60% and dampness becomes an issue, leading among other problems to mold growth, sleep discomfort, and muggy conditions, you can opt for the following solutions to solve the situation:

  • Use a crawl space dehumidifier to ensure structural stability is not compromised by excessive moisture in this specific area. You should also use a room dehumidifier that you can move from one area to another as needed and fix high RH wherever needed in the house.
  • If you have humidifiers, discontinue their use during the warmer seasons as it will lead to excess dampness indoors.
  • You can use air conditioners to make the environment feel cooler while also removing moisture from the air as most systems feature this capability.
  • Use exhaust fans to circulate the air and rid the atmosphere of excessive moistness in the process as well.


Whether you opt to maintain humidity within the stricter 45% to 55% range recommended by the ASHRAE, or you go for the 40% to 60% the or 30% to 50% ranges recommended by the EPA and scientists, it’s more of a preferential matter, what’s important in the end being to not allow RH levels to ever exceed 60% or drop below 30%.

As long as you follow these general guidelines, indoor humidity will provide you with comfortable living conditions and you won’t suffer any of the aforementioned repercussions, life quality enhancing as a result. Seeing how there are more than enough ways to upkeep RH within normal parameters, as we previously explained, you won’t have much trouble creating an ideal habitat for you to live in.

Tobey Hunter
Tobey Hunter
Tobey is the editor-in-chief at Optima Institute, his prior experience as a niche product reviewer in air quality improvement systems helping shape his path to conduct thorough research toward selecting and analyzing products so that customers are satisfied with the provided recommendations. During his carrier, Tobey also gathered technical input that makes him well versed in understanding advancements in modern systems, helping readers in turn to better understand how modern devices help improve life quality.