What's the best humidity level for a house?

What is the best humidity level for a house?

Between 30% and 50% relative humidity. The EPA recommends keeping indoor humidity below 60% if possible, and ideally between 30 and 50%.¹ The CDC sets the line a little lower: keep humidity as low as you can, no higher than 50%, all day long.²

Reading	What it means for mold
30 to 50%	The recommended range
50 to 60%	Above the CDC’s limit, still under the EPA’s ceiling. Worth watching
Above 60% for long periods	Above the EPA’s recommendation. Conditions where mold tends to start

Relative humidity is the percentage of water vapor the air holds compared with the most it could hold at that temperature. That’s why the same air reads higher in a cool room than a warm one, and why cold surfaces get wet first.

How do you measure indoor humidity?

With a hygrometer, also sold as a humidity meter or indoor thermometer with a humidity display. The EPA describes them as small, inexpensive instruments available at many hardware stores.¹

To get useful readings:

1. Give it some time to settle after you move it.
2. Keep it away from the shower, stove, kettle and direct sun.
3. Check at the same times of day, morning and evening, for a week.
4. Move it between rooms and compare.

Two inexpensive meters sitting side by side often won’t show exactly the same number, so watch the trend and the difference between rooms rather than chasing a single reading. A spike after a shower or while cooking is normal. What matters is humidity that stays above the range for hours, or one room that consistently reads higher than the others.

Is humidity different in coastal and Valley homes?

Often, yes, though every house is different. Homes near the coast, from Santa Monica to Long Beach, sit in cooler, damper air for much of the year, especially overnight and in the mornings. Indoor humidity tends to run higher, and cold glass and exterior walls collect condensation.

Homes in the San Fernando Valley and further inland usually see hotter, drier summers, and air conditioning removes moisture as it cools. Problems there are more often local: a bathroom without a working fan, a slow plumbing leak, or an AC drain that backs up. The EPA advises keeping AC drip pans clean and drain lines flowing.¹

How do you lower indoor humidity?

Remove moisture at the source and move air. The EPA’s steps:¹

• Vent clothes dryers, stoves and other moisture-producing appliances to the outside
• Run the bathroom fan or open a window when showering
• Use exhaust fans or open windows when cooking or running the dishwasher
• Use air conditioning or a dehumidifier when needed

The CDC adds that air should flow freely through the home and that kitchen and bathroom exhaust fans should vent outside.² Closets, the wall behind a bed or sofa, and the back of a cabinet on an exterior wall are where trapped humid air meets the coldest surfaces. The EPA lists wall surfaces behind furniture, where condensation forms, among the places hidden mold grows.¹ Pulling furniture a few inches off exterior walls and leaving closet doors open helps air reach the places that stay coolest.

Can indoor air be too dry?

The EPA’s ideal range has a floor of 30%. Below that is outside its recommendation, though it isn’t a mold concern; mold needs moisture to grow.¹ Dry spells are common in LA when hot, dry winds come through. If dry air is bothering you physically, that’s a question for your doctor, not a mold inspector.

When should you get a moisture assessment?

Not if your readings sit in the 30 to 50% range and nothing smells or looks damp. That’s the answer you want, and you don’t need us.

Consider a moisture and humidity assessment when one room stays above 60% after you’ve improved ventilation, when you see condensation on walls or in closets, or when there’s a musty smell and nothing visible. We take humidity and temperature readings in every room and compare them against a dry reference area, then trace high readings to a leak, condensation or a ventilation problem. Assessments start at $495 for one dwelling up to 2,000 sq ft. The mold check is a quick way to see where you stand first.