How long should you run a dehumidifier each day?

Run to a target, not a timer

Almost every modern dehumidifier has a humidistat. You set a target relative humidity, the unit runs until the room reaches it, then pauses and restarts when humidity rises. That way it runs as long as needed and no longer. For most rooms, 50 to 55 % RH is a sensible target. Our humidity settings guide gives targets by room.

A timer is useful as well as a target, for example to stop the unit running while you sleep in the same room, but the humidistat should do most of the work.

Typical patterns through the year

In winter, windows are cold and the heating is on, so moisture from cooking, washing and breathing condenses easily and the dehumidifier has more to do. In summer, open windows let moist air out, and many homes need it only for laundry.

Turning hours into kWh

Multiply the rated watts by the hours and divide by 1,000. A 350 W unit, such as the listed figure for the Meaco Arete Two 20L, uses 0.35 kWh an hour, so six hours is 2.1 kWh. A 175 W compact unit such as the Bosch Dry 1000 uses half that. Desiccant units draw more: the Meaco DD8L is listed at 660 W at full power.

Because the humidistat switches the unit off when the target is met, the real hours are usually lower than the time it is switched on. Try your own figures and unit rate in the running-cost calculator, and see dehumidifier running costs for more.

Best low energy dehumidifiers →

Can you leave a dehumidifier on all the time?

Yes, provided it is on a humidity target rather than continuous mode, and the water has somewhere to go. Most units switch off when the tank is full; with a drain hose to a sink or drain, they can run unattended for long periods. Keep the air inlet and outlet clear and the filter clean.

Continuous mode, which ignores the target, is for short jobs such as drying out after a leak. Left on all the time it wastes electricity and can make a room uncomfortably dry.

Note:Follow the maker's guidance on leaving the unit running unattended, plug it straight into a wall socket and keep it away from water spills.

Settings for summer

In warm weather, a compressor unit works efficiently, so it will reach the target quickly. Keep the same 50 to 55 % RH target and you may find it runs only briefly. If your home stays dry, switch it off and empty and dry the tank. If you have a cellar or ground floor that is humid in summer, a target of around 55 % RH is usually enough.

• Keep the target, not continuous mode
• Use laundry mode on washing days
• Close windows in the room being treated while it runs
• Store it clean and dry if not needed

Signs it needs to run longer

If windows still stream every morning, mould returns in corners, or washing takes days, the target may be too high, the unit may be undersized, or it may be too far from the problem. Try a lower target, move it closer, and keep the door shut. See what size dehumidifier you need and where to put a dehumidifier.

Frequently asked questions

How many hours a day should a dehumidifier run? As many as it needs to hold your target humidity. Set 50 to 55 % RH and let the humidistat decide; hours vary by season.

Is it OK to run a dehumidifier overnight? Yes. Use night or quiet mode in a bedroom, and make sure the tank will not overflow or a drain hose is fitted.

Should I run a dehumidifier in summer? Only if humidity is high. Keep the same target and it will run little. Switch it off if the home stays dry.