The ideal indoor humidity level, according to the U.S. Environmental Protection Agency, is below 60 percent relative humidity, ideally between 30 and 50 percent. ENERGY STAR gives the same 30 to 50 percent range and adds one important exception: in colder climates during the heating season, it says humidity should sit between 30 and 40 percent to prevent window condensation. So if there is water on your windows every morning in winter, your house may be inside the general range and still too humid for the weather outside. That is the part most humidity charts leave out.
This guide covers what those numbers mean, how to measure your own, what morning condensation is telling you, and where the fix stops being a homeowner job.
What "relative humidity" actually measures
ENERGY STAR's dehumidifier guidance (read 2026-09-27) defines relative humidity (RH) as "the amount of water vapor present in the air compared to the greatest amount of water vapor the air can hold at that temperature."
The key words are "at that temperature." Warm air can hold more water than cold air. The same amount of moisture that reads as a comfortable 40 percent in a warm living room can reach saturation right next to a cold pane of glass, because the air touching the glass cools down. When air cools past the point where it can hold its water, the water comes out as condensation.
That is why humidity is never just one number for a whole house. It changes by room, by time of day and by the temperature of the surfaces around it.
The ideal indoor humidity level, by source
The EPA's A Brief Guide to Mold, Moisture and Your Home (read 2026-09-27) and ENERGY STAR's guidance agree on the core range. Here they are side by side.
| Source | What it says | Read |
|---|---|---|
| EPA, A Brief Guide to Mold, Moisture and Your Home | Keep indoor humidity below 60 percent, ideally between 30 and 50 percent relative humidity | 2026-09-27 |
| ENERGY STAR, dehumidifier guidance | The optimum RH level for a building is generally considered to be between 30 and 50 percent | 2026-09-27 |
| ENERGY STAR, same page | In colder climates, during the heating season, 30 to 40 percent RH to prevent window condensation | 2026-09-27 |
You will find other ranges online, including 40 to 60 percent on some manufacturer and HVAC company pages. Where those differ from the EPA and ENERGY STAR figures above, we go with the agencies, and we would suggest you do too.
The EPA's advice comes from its mold and moisture guidance, which is why it frames the ceiling at 60 percent. ENERGY STAR notes that anything above its 30 to 50 percent range "may promote mold growth." In plain terms: the top of the range is about moisture damage, not comfort.
How to measure the humidity in your house
You cannot judge humidity by feel with any accuracy. The EPA's Mold Course notes that humidity can be measured with a humidity gauge or meter, and that models reading both temperature and humidity are sold at hardware stores. These are usually called hygrometers.
A few habits make the readings useful:
- Measure in more than one room. Bathrooms, kitchens, bedrooms and basements often read very differently.
- Measure at different times. Early morning, after showers and while cooking will show the peaks.
- Keep it away from direct sources. A meter next to a kettle or a shower door tells you about the kettle, not the room.
- Watch the trend, not one reading. A few days of readings tell you far more than a single number.
If you have a dehumidifier, ENERGY STAR notes that all ENERGY STAR certified models include a built-in humidistat that lets you set the RH level you want for the room.
Water on the windows every morning: what it means
This is the question that brings most people here. The short answer is that window condensation is a sign the air near the glass has more moisture than it can hold at the glass's temperature. It is not automatically a disaster, but the EPA's advice is clear: if you see condensation or moisture collecting on windows, walls or pipes, act quickly to dry the wet surface.
Why winter makes it worse
As the outside temperature drops, the inside surface of the glass gets colder. The colder the glass, the less humidity the room can carry before water appears on it. That is exactly why ENERGY STAR lowers its recommendation to 30 to 40 percent in colder climates during the heating season. A reading of 45 percent that caused no trouble in October can fog every window in January.
Older or single-pane windows, metal frames and the bottom corners of the glass usually run coldest, so that is where condensation tends to show first.
Reading where the water appears
Where condensation shows up is a useful clue, as long as you treat it as a starting point rather than a diagnosis:
| Where you see it | What it often points to |
|---|---|
| Every window in the house, every cold morning | Whole-house humidity is too high for the outdoor temperature |
| Mostly bedroom windows, first thing in the morning | Overnight moisture from breathing, with doors closed and little air movement |
| Mostly bathroom and kitchen windows | Moisture from showers and cooking is not being exhausted |
| Between the panes of a double-pane window | A failed window seal, which is a window problem, not a humidity one |
| On walls, closet corners or behind furniture | Cold surfaces; worth checking for mold and insulation gaps |
When condensation becomes a problem
A little fog that clears by mid-morning is common. Water that runs down the glass and pools on sills day after day is different: it can stain and rot wooden sills and frames and keep surfaces damp enough for mold. If you see dark spots on sills, peeling paint around the window or musty smells, treat the humidity as a real issue rather than a seasonal nuisance.
Where the extra moisture comes from
The EPA's mold guide lists practical moisture controls. The ones most homeowners can act on:
- Showers. The EPA advises running the bathroom fan or opening a window when showering.
- Cooking and dishwashing. The EPA recommends using exhaust fans or opening windows when cooking, running the dishwasher or dishwashing. If your range hood only recirculates air, it filters grease but does not remove moisture; our guide to ducted vs ductless range hoods explains how to tell which you have.
- Clothes dryers and other appliances. The EPA advises venting moisture-producing appliances such as clothes dryers and stoves to the outside where possible. A dryer with a clogged airflow path runs longer and pushes out damp air more slowly; our guide on cleaning the dryer lint trap and the housing behind it covers the part you can reach.
- Air conditioners and dehumidifiers. The EPA says to use them when needed.
- Cold pipes. The EPA recommends covering cold surfaces, such as cold water pipes, with insulation.
Other common contributors include drying laundry indoors, many houseplants in one room and a humidifier set too high. That last one matters in winter, when people add moisture for comfort and end up with wet windows.
What about air that is too dry?
In winter, many homes swing the other way and read below 30 percent. Both agencies put the lower bound of their range at 30 percent, so dry air also falls outside the recommended band. If you use a humidifier, watch the windows: they are usually the first place a too-high setting shows up. Keep the humidifier clean according to its manual, since a standing reservoir is its own moisture source.
If dry air or damp air seems to be affecting anyone's health or breathing, that is a question for a doctor, not for a humidity chart. We are not in a position to say what level suits a particular person.
When the fix is not yours
Adjusting habits, running fans longer and using a dehumidifier are homeowner steps. Some causes need a professional:
- Exhaust fans that do not vent outside, or ducts that are disconnected. A contractor or a licensed electrician, depending on the work.
- Dryer vents that need rerouting or replacement. A qualified installer.
- Cold walls, poor insulation or air leaks. An insulation or weatherization contractor.
- Failed window seals or rotted frames. A window contractor.
- Persistent high humidity tied to the heating or cooling system. A licensed HVAC contractor.
- Mold that has spread. The EPA says that if the moldy area is less than about 10 square feet, in most cases you can handle it yourself, and that mold or water damage caused by sewage or other contaminated water calls for a professional.
Whether any of that work needs a permit depends on your city or county. Your local building department can tell you what applies where you live. For the smaller recurring checks, our home maintenance checklist is a good place to add a seasonal humidity reading.
FAQ
What is the ideal indoor humidity level?
The EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent relative humidity. ENERGY STAR gives the same 30 to 50 percent optimum.
What humidity should my house be in winter?
ENERGY STAR says that in colder climates during the heating season, humidity should be between 30 and 40 percent RH to prevent window condensation.
Is condensation on windows in the morning bad?
Light fog that clears quickly is common. The EPA advises acting quickly to dry condensation on windows, walls or pipes, and daily pooling on sills suggests humidity is too high for the outdoor temperature.
How do I check the humidity in my house?
Use a humidity meter, often called a hygrometer. The EPA notes that models measuring both temperature and humidity are sold at hardware stores. Take readings in several rooms at different times.
Is 60 percent humidity too high indoors?
The EPA's guidance is to keep indoor humidity below 60 percent, and ENERGY STAR notes that levels above its 30 to 50 percent range may promote mold growth.
