Dehumidifier in Summer vs Winter: Settings, Timing & Best Humidity

Whether you need a dehumidifier depends on the indoor humidity, not the calendar. EPA recommends keeping indoor humidity below 60%, ideally between 30% and 50%. Mayo Clinic gives the same 30 to 50% range for comfort and health, and notes that air that is too dry irritates the nose and throat. So the goal in every season is the same band. What changes is which direction the air drifts.

In summer, warm air holds a lot of moisture and humidity climbs, especially in basements. In winter, heated indoor air is usually dry, and a dehumidifier is often unnecessary except in basements, crawl spaces and homes with condensation problems.

Sources: EPA Mold Course, Chapter 2 ("below 60 percent, ideally between 30 percent and 50 percent"); ENERGY STAR ("The optimum RH level for a building is generally considered to be between 30% and 50%").

Using a dehumidifier in summer

Use of dehumidifier in summer is where most of the benefit comes from. Warm, humid outdoor air leaks in, and when it reaches a cool basement its relative humidity rises. That is why basements smell musty in July and August.

• Set it to 45 to 50%. That is inside EPA's ideal range with a little margin.
• Use continuous drain (hose or pump) so the unit does not stop when the bucket fills.
• Close basement windows on humid days. Opening them lets in more moisture than it lets out.
• Keep it away from the AC thermostat, because it gives off warm air.

Dehumidifier in winter

Using a dehumidifier in winter makes sense in three cases:

• Condensation on windows. Water running down the inside of the glass every morning means indoor humidity is high for the outdoor temperature. EPA advises acting quickly when condensation collects on windows, walls or pipes.
• Damp basements and crawl spaces that stay humid all year.
• Drying laundry indoors. A dehumidifier speeds drying and keeps the moisture out of the walls.

Watch the temperature. Standard compressor units lose capacity in cool rooms and many list a minimum around 38 to 41F; below that, the coil can ice up. For a cold garage or crawl space, a desiccant dehumidifier or a low-temperature crawl space unit is the better choice. If a heated living space reads below 30%, turn the dehumidifier off.

Signs you need a dehumidifier

A cheap digital hygrometer is the best way to know, but these are the usual signs in any season:

• A musty or earthy smell, especially in the basement.
• Water beading on windows, cold-water pipes or the toilet tank.
• Mildew spots on bathroom ceilings, closet walls or stored items.
• Clothes, towels and bedding that never feel quite dry.
• A hygrometer reading above 50% for days at a time, or above 60% at any time.

If you see these in summer, a dehumidifier will usually fix them. If you see condensation in winter but humidity is in range, the problem may be a cold surface (single-pane windows, an uninsulated wall) rather than the air, and ventilation helps.

Spring and fall

The shoulder seasons are when people forget about the dehumidifier. In spring, ground moisture and rain push basement humidity up before the AC is running. In fall, cool nights and warm, humid days can leave a basement damp for weeks. Leave the unit on Auto at 45 to 50% through both seasons and empty or check the drain regularly. Clean the filter at the start of each season, and before you store it for winter, empty the bucket and let it dry out completely so mildew does not grow inside.

Best settings by season

What setting should a dehumidifier be on? For most homes, a target of 45 to 50% on Auto works all year. Avoid Continuous mode unless you are drying out after a leak, because it ignores the humidistat and keeps running.

Pairing with AC/heating

With AC in summer, the air conditioner removes some moisture while it cools. If the house still feels clammy with the AC on, often because the AC is oversized and cycles off too quickly, run a dehumidifier to hold humidity down so you can set the thermostat a little higher. In winter, heating lowers relative humidity on its own, so the dehumidifier usually has little to do upstairs. Our portable AC guide covers dry mode and when to use each.

Pros and cons of year-round use

The simple rule: leave it on Auto at 45 to 50% and let the humidistat decide. In a dry, heated room it will barely run. For costs, see our running costs guide.