A dehumidifier ices up when the cooling coils drop below freezing while pulling moisture from the air
When a dehumidifier runs in cold conditions, the evaporator coils inside get very cold as they remove humidity. If the air temperature falls below about 65°F, or if the coils get too cold too fast, moisture on those coils freezes into ice instead of draining away as water. Once ice builds up, it blocks airflow through the unit, the dehumidifier stops working, and it may shut itself off or run without removing any moisture at all.
This is not a sign the dehumidifier is broken—it is a normal response to operating outside the conditions it was designed for. Most household dehumidifiers work best between 65°F and 85°F. Below that range, icing becomes likely. The colder the room, the faster ice forms.
Key Takeaways
- Dehumidifiers ice up when room temperature drops below 65°F because the cooling coils freeze moisture instead of letting it drain.
- Running a dehumidifier in a basement, garage, or unheated space in winter or early spring is the most common cause of icing.
- Many modern dehumidifiers have an automatic defrost cycle that melts ice and restarts the unit, but older models do not.
- The simplest fix is to raise the room temperature above 65°F or move the dehumidifier to a warmer space.
- If you need to dehumidify a cold space, look for a dehumidifier with a low-temperature defrost feature or consider a desiccant model instead.
Why cold air causes ice to form on the coils
A dehumidifier works by pulling warm, humid air across very cold evaporator coils. The moisture in the air condenses on those coils the same way water beads up on a cold window. Normally, that condensed water drains into a tank or out a hose. But when the room is cold, the coils become so cold that the water freezes before it can drain. Ice builds up layer by layer until it covers the coils completely.
The problem gets worse because ice is an insulator. Once a thick layer forms, it prevents the coils from making contact with the air, so the unit stops removing humidity. At that point, the dehumidifier is just running in place, using energy but doing no work.
The exact temperature at which icing starts depends on humidity level and how fast air moves across the coils, but 65°F is the practical threshold for most units. Below that, icing is likely. At 50°F or lower, it is almost certain.
Common situations where dehumidifiers ice up
Basements are the most common place for icing problems. Basements stay cool year-round, and in spring and fall they are often damp and cold at the same time—exactly the conditions that cause icing. A dehumidifier running in a 55°F basement in March will ice up within hours.
Garages, crawl spaces, and unheated storage rooms cause the same problem. So do attics in winter, even though attics are usually dry. If you run a dehumidifier in any space where the temperature regularly drops below 65°F, icing is likely.
Icing can also happen indoors if you run the dehumidifier in a very cold corner of a room, near an outside wall in winter, or near an air conditioning vent that cools the surrounding air. The unit itself may be in a warm room, but if cold air is blowing directly across it, the coils can still freeze.
How automatic defrost cycles work
Many dehumidifiers made in the last ten years have a built-in automatic defrost cycle. When the unit senses ice forming on the coils, it reverses the refrigeration cycle or shuts off the compressor and runs a fan to warm the coils. The ice melts, drains away, and the unit restarts. This happens automatically without you doing anything.
The defrost cycle usually takes 15 to 30 minutes. During that time, the dehumidifier is not removing moisture—it is just melting ice. If the room stays cold, the cycle repeats every hour or so. This means the unit spends more time defrosting than dehumidifying, which is why it is inefficient in cold spaces even if it has a defrost feature.
Older dehumidifiers do not have this feature. If your unit is more than 10 to 15 years old and ices up, it will stay iced until you manually defrost it by unplugging it and letting it sit in a warm room for a few hours.
Manual defrosting if your dehumidifier freezes solid
If your dehumidifier ices up and does not have an automatic defrost cycle, unplug it and move it to a warm room—ideally 70°F or warmer. Leave it unplugged for at least two to four hours. The ice will melt and drain out the bottom or into the collection tank. Do not try to chip ice off the coils; you will damage the fins and the refrigerant lines.
Once the ice is gone, plug the unit back in and let it run for 15 minutes in the warm room before moving it back to the cold space. This lets the coils warm up and stabilizes the refrigerant pressure inside. If you move it back to a cold room when ready, it will ice up again within minutes.
If your dehumidifier keeps icing up every time you use it, manual defrosting is not a practical solution. You need to either raise the room temperature or switch to a different type of dehumidifier.
Choosing the right dehumidifier for cold spaces
If you need to dehumidify a basement or other cold space, look for a dehumidifier labeled as having low-temperature operation or low-temperature defrost. These units are designed to work down to 50°F or even lower. They cost more than standard models, but they will not ice up in cold conditions.
Another option is a desiccant dehumidifier. These units do not use refrigeration coils at all. Instead, they pull air through a moisture-absorbing material (usually silica gel). Desiccant models work well in cold spaces because there are no coils to freeze. They are quieter than refrigerant models and work better in temperatures below 60°F. The trade-off is that they use more energy and are less effective in warm, humid conditions.
If you are dehumidifying a basement in winter, raising the room temperature is often the simplest fix. Even heating the space to 65°F with a small space heater will stop icing and let a standard dehumidifier work normally. The cost of running a heater is usually less than replacing a dehumidifier that keeps icing up.
Preventing ice buildup before it starts
The best way to avoid icing is to check the room temperature before you run the dehumidifier. If it is below 65°F, do not turn the unit on. Wait until the space warms up, or move the dehumidifier to a warmer location.
If you must run a dehumidifier in a cold space, check it every 30 minutes for the first hour. If you see frost or ice forming on the outside of the unit or around the air intake, unplug it when ready. The sooner you stop it, the less ice builds up and the faster it will defrost.
Keep the dehumidifier away from outside walls, windows, and air conditioning vents in cold months. Even if the room feels warm, cold air near those surfaces can cause localized icing. Place the unit in the center of the room or against an interior wall.
Frequently Asked Questions
Will a dehumidifier with automatic defrost work in my cold basement?
It will work, but not efficiently. The unit will spend 15 to 30 minutes of every hour defrosting instead of removing moisture. If your basement is consistently below 65°F, a low-temperature dehumidifier or a desiccant model will give you much better results.
Can I leave a dehumidifier running overnight in a cold garage?
Not safely. If the garage temperature drops below 65°F at night, the dehumidifier will ice up and may not defrost on its own if it does not have an automatic cycle. Unplug it before you leave, or move it to a heated space.
Does ice on a dehumidifier mean it is broken?
No. Icing is a normal response to cold conditions, not a sign of a mechanical failure. Once the unit defrosts and you move it to a warmer space, it will work normally again.
What temperature should my basement be to safely run a dehumidifier?
Keep the space at 65°F or warmer. At that temperature, most standard dehumidifiers will not ice up. If your basement is naturally colder, a low-temperature or desiccant model is a better choice.
How long does it take for a frozen dehumidifier to defrost?
In a warm room (70°F or higher), most units defrost completely in two to four hours. Thicker ice takes longer. Do not try to speed up the process with heat guns or hot water; let it melt naturally to avoid damaging the coils.