Ideal Humidity for Home: What Level Feels Best?

The short answer

The ideal humidity for home falls between 30 and 50% relative humidity, and the EPA advises keeping it below 60% (EPA Mold). For comfort and health together, a review in Environmental Health Perspectives suggested 40 to 60% (Arundel 1986). The sweet spot where those overlap, roughly 40 to 50%, works well for most homes in most seasons.

What indoor humidity do experts recommend?

Different groups set slightly different targets because they protect against different problems:

• EPA: keep indoor humidity "below 60 percent (ideally between 30 and 50 percent)" to prevent mold (EPA Mold). For humidifiers, the EPA adds a firmer cap: don't humidify past 50% (EPA Humidifiers).
• ASHRAE Standard 55: the engineering standard for indoor comfort sets an upper limit of 0.012 humidity ratio (about 12 grams of water per kilogram of dry air) in its graphical comfort method, and no lower limit at all (ASHRAE IC 55-2010-1).
• Arundel and colleagues: after reviewing studies on germs, allergens and indoor chemicals, they concluded that holding indoor humidity between 40 and 60% would minimize most humidity-related health effects (Arundel 1986).

Relative humidity tells you how full the air is with water vapor compared to the most it could hold at that temperature. So 50% means half full. Warm air holds more water than cool air, which explains why the same moisture reads differently as a room heats up or cools down.

Humidity ranges and what happens at each

| Indoor relative humidity | What tends to happen | |---|---| | Below 30% | Drier than the EPA's ideal range. Dry nose, throat, lips and skin, plus static shocks, show up as common winter complaints (EPA Humidifiers). | | 30 to 40% | Inside the EPA's ideal range (EPA Mold). Comfortable for many people, on the drier side. | | 40 to 50% | Inside both the EPA and Arundel ranges. Dust mite populations stay small below 50% (Arundel 1986). | | 50 to 60% | Under the EPA's 60% ceiling, but above its 50% humidifier cap. The EPA warns that extra moisture encourages dust mites and mold (EPA Humidifiers). | | Above 60% | Over the EPA ceiling. Most fungi need humidity above 60% to grow (Arundel 1986). | | Around 80% | Dust mite populations reach their maximum size (Arundel 1986). |

Why humidity changes how a temperature feels

Your body cools itself mostly by sweating, and sweat only cools you when it evaporates. Sleep researchers put it plainly: lower humidity lets sweat evaporate and carry heat away, while higher humidity stops evaporation and leaves the skin wet (Okamoto-Mizuno 2012). Wet skin that won't dry means you hold on to heat.

That explains why 78°F feels pleasant in a dry desert house and sticky in a muggy one. A Department of Energy project put a number on it: at a common summer thermostat setting of 75°F (24°C), higher indoor humidity can shift how warm the air feels by 11°F (6°C) (DOE Building America 2013). The same physics drives the heat index outdoors, which our guide to the feels like temperature covers in detail.

Humidity forms one piece of why the perfect temperature changes from day to day. Just Right picks a Tesla cabin and Apple Home thermostat setting based on weather, sun and time of day.

Signs your air is too dry or too humid

Too dry

• Dry nose, throat, lips or skin (EPA Humidifiers)
• Static shocks when you touch a doorknob (EPA Humidifiers)
• Peeling wallpaper and cracks in paint and furniture, which the EPA lists among winter heating nuisances (EPA Humidifiers)

Too humid

• Water condensing on windows, walls or pictures (EPA Humidifiers)
• A musty smell or visible mold, since most fungi grow once humidity passes 60% (Arundel 1986)
• Worse indoor allergies, because dust mites multiply in damp air (Arundel 1986; EPA Humidifiers)
• Air that feels clammy or sticky even when the thermostat reads a normal number (DOE Building America 2013)

Summer vs winter humidity targets

The target range stays the same year round: 30 to 50%, and below 60% (EPA Mold). Only the direction you push changes.

Summer. Warm, humid outdoor air leaks in, so you usually fight too much moisture. The EPA recommends air conditioners and dehumidifiers when needed (EPA Mold). Many people crank the air conditioner colder to dry the air, but a DOE field study found this "not always effective" for controlling humidity or comfort. Pairing a dehumidifier with the air conditioner improved comfort and cut utility costs in a Florida home (DOE Building America 2013).

Winter. Cold air carries little water, and in cold climates, keeping indoor humidity in the healthy range often requires a humidifier (Arundel 1986). Watch your windows. When condensation forms, the EPA says to move the humidifier, lower its setting or run it less (EPA Humidifiers).

What is the best humidity for sleeping?

The EPA's whole-house range of 30 to 50% applies to the bedroom too (EPA Mold). The research leans toward avoiding damp heat. When sleepers slept in warm, humid air (90°F, or 32°C, at 80% humidity) compared with cooler air (79°F, or 26°C, at 60%), they woke more, got less deep and REM sleep, and their core temperature dropped less than it should overnight (Okamoto-Mizuno 2012).

The same review notes that during normal sleep, the pocket of air under your covers tends to sit around 90 to 93°F (32 to 34°C) at 40 to 60% humidity (Okamoto-Mizuno 2012). Heavy blankets in a humid room push that pocket past comfortable. For temperature targets, see our guide to the best temperature for sleep.

How to measure humidity at home

Buy a hygrometer. These small, inexpensive gauges sell at hardware stores, and some humidifiers include a built-in humidistat you can set to a target (EPA Humidifiers). A few tips:

• Put it in the rooms you use most, away from the shower, stove and kettle.
• Check it at different times of day. Cooking, showers and laundry all add bursts of moisture.

How to fix humidity that's off

To lower humidity

• Run an air conditioner or a dehumidifier (EPA Mold).
• Turn on the bathroom fan or open a window while you shower, and use exhaust fans while you cook or run the dishwasher (EPA Mold).
• Vent clothes dryers, stoves and other moisture-producing appliances outside where possible (EPA Mold).
• Open doors and windows when practical, and use fans to keep air moving (EPA Mold).

To raise humidity

• Use a humidifier, and set it no higher than 50% (EPA Humidifiers).
• Fill it with low-mineral water such as distilled water, which keeps minerals out of the air (EPA Humidifiers).
• Empty, wipe dry and refill portable units daily, and clean them every third day (EPA Humidifiers).
• Take extra care with ultrasonic and impeller ("cool mist") models, which most readily spread microorganisms and minerals into the air (EPA Humidifiers). Arundel's review favored evaporative or steam humidifiers for the same reason (Arundel 1986).

If you live with asthma or allergies and your symptoms change when you adjust humidity, mention it to your clinician.

The bottom line

Aim for 30 to 50% indoor humidity, keep it under 60%, and land near 40 to 50% if you can. Dry the air with an air conditioner, dehumidifier and good ventilation in summer, and add moisture carefully with a clean humidifier in winter. A cheap hygrometer tells you which job you have. Know your numbers, and humidity belongs on the list.