You bought a dehumidifier because the bathroom ceiling had black spots, the bedroom windows dripped every morning, and your clothes took three days to dry on the airer. You plugged it in, turned it on, and… it collected some water. But the condensation is still there, the clothes are still damp, and you’re wondering whether you wasted £200 on a fancy bucket. The dehumidifier probably works fine — you’re just not using it right.
In This Article
- Where to Place Your Dehumidifier
- What Humidity Level to Set
- When to Run It
- Using a Dehumidifier to Dry Clothes
- Room Size and Dehumidifier Capacity
- Maintenance That Most People Skip
- Common Mistakes
- Dehumidifier Types and Which Works Best
- When a Dehumidifier Won’t Fix the Problem
- Frequently Asked Questions
Where to Place Your Dehumidifier
Placement is the single biggest factor in how well a dehumidifier works, and it’s where most people go wrong.
The Centre of the Room
Not against the wall. Not in a corner. Not behind the sofa. The dehumidifier needs airflow around all four sides to work efficiently. Most units draw air in through the back or sides and expel dry air from the front or top. Press it against a wall and you’re blocking the intake, forcing the compressor to work harder and extract less.
Leave at least 20-30cm of clear space around every side. If the room is large, place the unit roughly in the centre or wherever the air feels most humid.
Close the Doors and Windows
A dehumidifier treats the air in a specific volume. If the doors and windows are open, you’re trying to dehumidify the outdoors — an expensive and futile exercise. Close the room, let the dehumidifier do its job, and ventilate later.
There’s a common debate about dehumidifiers vs opening windows. The short answer: in summer, open windows can work. In winter, when outside air is cold and internal walls create condensation, a dehumidifier is more effective.
Near the Source of Moisture
If you know where the moisture is coming from — a drying rack of clothes, a steamy bathroom, a kitchen after cooking — place the dehumidifier as close to that source as practical. It’ll catch the moisture before it spreads and settles on walls and ceilings.
Elevated Position
Moist air rises. Placing the dehumidifier on a table or sturdy shelf (if the unit is small enough) can improve performance compared to floor level. This matters most in rooms with high ceilings. Don’t risk a heavy unit on an unstable surface, though — a 12kg compressor dehumidifier falling off a shelf is a bad day.
What Humidity Level to Set
Most dehumidifiers with a built-in humidistat let you set a target humidity. The Energy Saving Trust advises keeping indoor humidity below 60% to prevent mould-related health problems. The right setting is:
- 45-55% relative humidity — the sweet spot for UK homes. Comfortable for people, bad for mould, gentle on wooden furniture and flooring
- Below 40% — too dry. Can cause dry skin, static electricity, cracked wooden furniture, and respiratory discomfort. Your house shouldn’t feel like an aircraft cabin
- Above 60% — too humid. This is where mould thrives, dust mites multiply, and condensation forms on cold surfaces
If you don’t have a built-in humidistat, a standalone hygrometer (about £8-12 from Amazon UK) tells you the current humidity so you can decide whether the dehumidifier needs to run. Our guide to measuring humidity at home covers where to place the sensor and what the numbers mean.
Seasonal Adjustment
UK humidity varies enormously by season:
- Winter (October-March) — internal humidity often rises because windows stay closed, heating creates temperature differences that cause condensation, and activities like showering and cooking add moisture with nowhere to go. This is peak dehumidifier season
- Summer (April-September) — humidity may still be high (especially in August), but opening windows and natural ventilation often handles it. Run the dehumidifier less frequently or only when drying clothes indoors
When to Run It
Not 24/7
Running a dehumidifier continuously is unnecessary and expensive. A typical compressor unit draws 200-500W — roughly 5-12p per hour depending on the model and your electricity tariff. Running one 24/7 for a month costs £36-86. That’s a significant addition to your energy bill.
Instead:
- Run for 4-6 hours at a time — this is enough to bring humidity down in a single room
- Use the built-in humidistat — set your target (50%) and the unit switches off automatically when it’s reached, then restarts when humidity rises again
- Time it around moisture events — after showers, after cooking, while clothes are drying. These are the peak moisture periods
Best Times of Day
- Morning — overnight breathing and any open bedroom doors release moisture. Running the dehumidifier for 2-3 hours in the morning catches this
- During clothes drying — the most effective single use case. Keep it running until the clothes are dry
- After cooking — boiling pasta, steaming vegetables, and using the oven all pump moisture into the air
- After bathing — showers generate enormous amounts of moisture. If your bathroom doesn’t have an extractor fan (or has a weak one), a bathroom-specific dehumidifier makes a big difference
Using a Dehumidifier to Dry Clothes
This is the use case that surprises most new owners. A dehumidifier in a closed room with a clothes airer dries laundry far faster than air drying alone — often within 3-4 hours instead of 24+.
How to Set It Up
- Place the airer and dehumidifier in the same room
- Close the door and windows
- Set the dehumidifier to its highest extraction rate (continuous mode, not target humidity)
- If your unit has a laundry mode, use it — this typically runs the fan at high speed and disables the humidistat
- Position the dehumidifier so its dry air output blows toward the clothes. Air circulation is as important as moisture extraction
Cost vs Tumble Dryer
A tumble dryer costs roughly 60-70p per cycle (based on a 2,400W condenser dryer running for 90 minutes at current UK energy prices). A dehumidifier drying the same load costs roughly 20-30p (250W for 4 hours). Over a year of drying two loads per week, that’s a saving of about £35-50.
The dehumidifier is also gentler on clothes — no heat damage, no shrinkage, and delicates dry without worry. The only downside is speed: a tumble dryer is faster. But if you’re not in a rush, the dehumidifier wins on cost and clothing care. For the best models for drying clothes, we tested extraction rates specifically with laundry loads.
Room Size and Dehumidifier Capacity
Dehumidifiers are rated by extraction capacity — how many litres of water they can remove per day. Match this to your room size:
- 7-10 litres/day — suitable for small rooms (up to 15m²): bedrooms, bathrooms, small kitchens
- 12-16 litres/day — suitable for medium rooms (15-30m²): living rooms, larger bedrooms, open-plan kitchens
- 20+ litres/day — suitable for large spaces (30m²+): whole-floor areas, basements, garages, or homes with serious damp problems
Don’t Oversize
A massively oversized dehumidifier won’t work better — it’ll cycle on and off rapidly (short-cycling), which wastes energy and wears out the compressor faster. Match the capacity to your actual room size and humidity level.
Don’t Undersize
Conversely, a unit that’s too small will run continuously without reaching the target humidity. It’ll collect water — just not fast enough to make a noticeable difference. This is the most common buyer’s mistake: buying a £50 mini dehumidifier for a 25m² living room and wondering why it doesn’t work.
Maintenance That Most People Skip
Empty the Water Tank
Obvious, but many people let it fill up and then the unit shuts off automatically and sits idle for days before anyone notices. Check daily during heavy use. Better yet, use continuous drainage — most dehumidifiers have a hose outlet at the back. Run a hose from the unit to a sink, bath drain, or external drain, and you never need to empty the tank manually.
Clean the Filter
Every dehumidifier has an air filter that catches dust and debris. A clogged filter restricts airflow, reduces efficiency, and forces the compressor to work harder. Clean it every 2-4 weeks:
- Remove the filter (usually a pull-out panel at the back)
- Vacuum loose dust with a brush attachment
- Wash under running water if the manufacturer says it’s washable (most are)
- Let it dry completely before reinserting
Check the Coils
Once every 3-6 months, inspect the evaporator coils (visible behind the filter panel on most units). If they’re frosted or iced up, the unit is working in conditions that are too cold (below about 15°C for compressor models). If they’re caked in dust, the filter isn’t doing its job — clean both.
Service the Continuous Drain
If you use continuous drainage, check the hose for kinks, blockages, and algae growth. A blocked hose means the water backs up into the tank and the unit eventually shuts off. Flush the hose with diluted white vinegar every few months.
Common Mistakes
Running It in a Cold Room
Standard compressor dehumidifiers lose efficiency rapidly below 15°C, and below 10°C they struggle badly — the evaporator coils ice up and the unit goes into defrost mode repeatedly. For cold rooms (unheated bedrooms in winter, garages), you need a desiccant dehumidifier instead. See the section below.
Setting Humidity Too Low
Setting the target to 30% won’t dry the room faster — it’ll just keep the dehumidifier running longer than necessary. Below 40% causes its own problems: dry skin, cracked woodwork, and static. Set 50% and leave it.
Ignoring the Actual Problem
A dehumidifier manages symptoms. If your home has rising damp, leaking gutters, poor ventilation, or structural issues, the dehumidifier will fill its tank endlessly without fixing anything. Our guide to reducing damp and mould covers how to identify and fix the root causes.
Moving It Too Often
Let the dehumidifier work in one room until the humidity is under control before moving it to another. Moving it every few hours means no room gets properly treated. If you have multiple problem rooms, consider a second unit or running it for a full day in each room on a rotating schedule.
Dehumidifier Types and Which Works Best
Compressor (Refrigerant)
The most common type. Works by cooling air over coils so moisture condenses out — the same principle as your fridge. Effective in warm rooms (above 15°C), energy-efficient, and available in high capacities.
Best for: living rooms, bedrooms, kitchens, and any heated space during autumn and winter.
Desiccant
Uses a rotating desiccant wheel (like silica gel) to absorb moisture. Works at any temperature — including near-freezing. Uses slightly more electricity than compressor models (typically 500-700W) but performs in conditions where compressor units fail.
Best for: garages, conservatories, unheated spare rooms, caravans, and boats.
Which Should You Buy?
If your home is normally heated and you’re dealing with condensation, cooking moisture, or drying clothes — compressor. If you need a dehumidifier for cold spaces or year-round use in unheated areas — desiccant. The humidifier vs dehumidifier guide covers when you need each type of appliance.
When a Dehumidifier Won’t Fix the Problem
A dehumidifier is a tool, not a cure. It won’t fix:
- Rising damp — this needs a damp-proof course, which is a building job. A dehumidifier masks the symptoms temporarily
- Penetrating damp — water coming through walls from outside (leaking gutters, cracked render, failed pointing). Fix the exterior first
- Plumbing leaks — dripping pipes or slow leaks under floors add moisture constantly. The dehumidifier will run endlessly until the leak is found and fixed
- Inadequate ventilation — if your home has no extractor fans in the kitchen or bathroom, and windows are never opened, you’re generating more moisture than any domestic dehumidifier can handle. Fit extractor fans as a minimum, and consider a whole-home ventilation approach for sealed modern homes
If your dehumidifier fills its tank daily despite running for months, the moisture isn’t coming from humidity in the air — it’s coming from a structural or plumbing source. Investigate before spending more on a bigger dehumidifier.
Frequently Asked Questions
How long should I run a dehumidifier each day? For general humidity control, 4-6 hours per day is usually enough. Use the built-in humidistat to let the unit manage itself — set 50% and let it cycle on and off as needed. For drying clothes, run it continuously until the clothes are dry (typically 3-5 hours).
Should I leave a dehumidifier on overnight? If the room is particularly humid or you’re drying clothes, yes — it’s safe to run overnight. Modern dehumidifiers auto-shut when the tank is full. For general maintenance, overnight running is usually unnecessary and costs 50-70p per night in electricity.
Will a dehumidifier help with mould? It helps prevent new mould growth by keeping humidity below 60%. It won’t kill existing mould — you need to clean that with a mould treatment product first. Once the surface mould is removed, maintaining 45-55% humidity with a dehumidifier prevents it from coming back.
Can a dehumidifier be too big for a room? Yes. An oversized unit short-cycles (turns on and off rapidly), which wastes energy and wears out the compressor. Match the extraction rate to your room size: 7-10L/day for small rooms, 12-16L for medium, 20L+ for large spaces.
Why is my dehumidifier collecting no water? Three common causes: the humidity is already low (check with a hygrometer), the room temperature is too cold for a compressor model (below 15°C), or the filter is clogged and restricting airflow. Clean the filter first, then check conditions.