Dehumidifier Running But Humidity Not Dropping? Here's Why

Quick Answer

The most likely reason your dehumidifier is running without lowering humidity is that it's too small for the space. A unit rated for a bedroom won't make a dent in a basement. Other common causes include low room temperature (below 15°C / 60°F), a full or poorly draining water tank, dirty coils, and high moisture sources that outpace the unit's capacity.

The Sizing Problem

This is the number one issue I see, and it's entirely preventable. Dehumidifiers are rated by how many litres (or pints) of moisture they can extract from the air in 24 hours. That rating is tested under specific conditions — typically 30°C and 80% relative humidity — which are much more favourable than what most people's basements or laundry rooms actually experience.

In real-world conditions, your dehumidifier extracts significantly less moisture than its rated capacity.

If your unit falls short of these recommendations for your space and conditions, no amount of troubleshooting will help. You either need a larger unit or a second dehumidifier.

Temperature: The Hidden Factor

Most people don't realise that compressor-based dehumidifiers — which is what the vast majority of home units are — lose effectiveness dramatically as the temperature drops.

Here's why. These units work by pulling warm, humid air over cold coils. The moisture condenses on the coils and drips into the tank, just like water forming on a cold glass on a summer day. But when the air is already cold, the coils need to be even colder to create condensation. Below about 15°C (60°F), the coils get cold enough to frost over, and the unit spends most of its time in defrost mode rather than actually removing moisture.

This is why dehumidifiers often seem useless in unheated garages, basements in winter, or poorly insulated spaces.

Tip

If you need to dehumidify a cold space (below 15°C / 60°F), look for a desiccant dehumidifier instead of a compressor model. Desiccant units use a moisture-absorbing material rather than cold coils, so they work effectively even at low temperatures. They cost more to run, but they actually work in the conditions where compressor units fail.

Placement Mistakes

Where you put the dehumidifier affects how well it works. The unit needs airflow — it pulls air in from one side and blows drier air out the other. If those intakes or outlets are blocked, efficiency drops.

Common placement errors:

Pushed up against a wall. Leave at least 20 to 30 cm (8 to 12 inches) of clearance on all sides.
In a corner where air doesn't circulate. The unit dehumidifies the air immediately around it but can't reach the rest of the room.
Near a door or window that's frequently opened. You're fighting a constant stream of fresh humid air.
On the wrong floor. Humid air rises, but moisture sources (like damp floors or water ingress) are at ground level. Place the unit near the moisture source.

If your space is large or has an unusual layout — like an L-shaped basement — the dehumidifier may not be able to circulate air to all areas. A standalone fan can help move humid air toward the unit.

Check the Obvious Things

Before assuming something is wrong, run through this quick checklist:

Is the tank full? Most dehumidifiers stop extracting when the tank is full, even if they keep the fan running. The unit sounds like it's working, but it isn't. If you're not using a continuous drain hose, you may need to empty the tank more frequently than you expect.

Is the continuous drain actually draining? If you've connected a drain hose, check that it's not kinked, clogged, or routed uphill. Gravity drain hoses need a continuous downhill path. Even a small sag in the middle of the hose can create a blockage.

Are the coils dirty? Pull out the filter and look at the coils behind it. If they're coated in dust, the unit can't transfer heat efficiently. Clean the filter every two weeks and vacuum the coils every few months.

Is the humidity sensor accurate? The built-in hygrometer on many dehumidifiers is only approximate. Buy a cheap standalone hygrometer and place it across the room from the dehumidifier. You might find the room humidity is actually lower than the unit's display suggests, or that the unit is only dehumidifying the air in its immediate vicinity.

Moisture Sources You Might Be Overlooking

Sometimes the dehumidifier is working perfectly but it's fighting a losing battle against a continuous moisture source.

In basements:

Water seeping through foundation walls or floor (look for damp patches, efflorescence, or staining)
A sump pump that isn't keeping up
Uninsulated cold water pipes dripping with condensation
A dryer venting indoors

In bathrooms and laundry rooms:

A bathroom fan that's undersized, broken, or not ducted outside (poor bathroom ventilation also causes paint to peel off the ceiling)
Drying clothes indoors (a single load of washing releases 2 to 5 litres of water into the air)
Poor grouting or sealant allowing moisture behind tiles

General:

Cooking without using an extractor fan
High occupancy (each person releases about 40ml of moisture per hour just by breathing)
Houseplants (a large collection of plants adds meaningful moisture)

If you have a significant moisture source, the correct fix is to address the source rather than trying to overpower it with dehumidification.

When the Unit Itself Is Failing

If you've ruled out sizing, temperature, placement, and moisture sources, the dehumidifier itself may be failing. The most common mechanical issues:

Refrigerant leak. If the coils are barely cold to the touch when the unit has been running for 30 minutes, the refrigerant may have leaked. This is usually not economical to repair — replacement is the better option.

Failing compressor. The unit runs, the fan blows, but the compressor either doesn't start or cycles on and off every few minutes. You might hear clicking or humming without the compressor engaging.

Faulty humidistat. The sensor that measures humidity may have drifted. The unit thinks the room is already at the target humidity, so it doesn't run the compressor. Setting the target to the lowest possible setting can confirm this — if the unit suddenly starts working harder, the sensor is the issue.

Warning

If your dehumidifier is more than 7 to 8 years old and not performing well, replacement is usually more cost-effective than repair. Newer models are significantly more energy-efficient, which means lower running costs that partially offset the purchase price.

What Humidity Level Should You Target?

For most homes, you want to maintain indoor relative humidity between 40% and 60%. Below 40% and you'll notice dry skin, static electricity, and cracking wood. Above 60% and you create conditions that favour mould growth, dust mites, and musty odours.

In a basement that's used only for storage, keeping humidity below 60% is sufficient. In living spaces, 45% to 55% is the comfortable range for most people. If you are also noticing that your thermostat says one temperature but the room feels different, humidity levels are often part of that disconnect -- dry air feels cooler at the same temperature.