Why Is There Condensation on My Windows?

First, find where the moisture is

Run a dry finger across the glass. The location of the moisture is the single most useful clue.

• Inside surface (room side): usually an indoor humidity and air-movement issue.
• Between the panes: the sealed unit has likely lost its seal. Wiping won't help.
• Outside surface: typically harmless, caused by outdoor dew. It often appears on efficient windows because the outer pane stays cool.

Why it happens indoors

Everyday activities add moisture to indoor air: showers, cooking, drying laundry, houseplants, and simply breathing. In cold weather, window glass is often the coldest surface in a room, so that moisture condenses there first.

Occasional light fogging during a cold snap is common. Persistent dripping, pooling on sills, or dark spots on frames deserve attention, because ongoing moisture can damage wood, paint, and drywall and can support mold growth.

Sensible steps you can take

• Measure your indoor humidity with an inexpensive hygrometer so you're working from a number, not a guess.
• Run bathroom and kitchen exhaust fans during and after showers and cooking.
• Make sure clothes dryers vent outdoors.
• Open blinds and curtains during the day so warmer room air can reach the glass.
• If you use a humidifier, turn it down during very cold weather.
• Wipe up water on sills promptly so it doesn't soak into wood or paint.

What humidity level should I aim for?

The EPA's guidance on indoor moisture suggests keeping indoor relative humidity below 60 percent, ideally between 30 and 50 percent. In very cold weather, you may need to stay toward the lower end of that range to keep windows clear. Check the source linked below for the current recommendation.