The right apartment dehumidifier size for most small flats is 10L to 12L per day. A 10L unit is a common choice for a one- or two-bedroom flat with light condensation, and a 12L unit gives more headroom if you dry laundry indoors, have more than two people at home, or have a serious moisture problem.
Larger open-plan apartments or very heavy moisture loads may need more. Check your real humidity with a hygrometer before you buy.
What Apartment Dehumidifier Size Do You Need?
Match capacity to floor area, moisture level, and how much moisture you create each day. Cooking, showers, indoor clothes drying, poor ventilation, and cold external walls all raise the load. ENERGY STAR explains that the capacity you need depends on both the size of the space and how damp it is.
In the UK, compact units are usually rated in litres per day. In the US, capacity is listed in pints per day. Roughly, 10L is about 21 US pints and 12L is about 25 US pints. The two systems use different test conditions, so treat that as an approximation, and do not confuse a 10L rating with a 10-pint model. The litre figure is daily moisture removal, not the size of the water tank.
| Apartment condition | Starting size | Good fit for |
|---|---|---|
| Light condensation, no musty smell, humidity usually below 60% | 10L per day | Studio, small one-bedroom, mild seasonal damp |
| Regular window condensation, indoor laundry, more than two occupants, or humidity often above 60% | 12L per day | Many one- to two-bedroom flats with a higher daily moisture load |
| Open-plan layout, larger flat, or heavy laundry drying | 15L to 20L per day (rule of thumb) | Larger apartments or unusually high moisture generation |
| Wet walls, leaks, water staining, or spreading mould | Do not size by appliance alone | Find and fix the water source first |
The manufacturer Meaco makes a similar recommendation in its flat buying guide: a 10L dehumidifier for a one- or two-bedroom flat, and sometimes 12L for a serious moisture problem or more than two occupants.
If you buy a US-rated model, remember that ENERGY STAR notes DOE test changes lowered pint ratings starting in 2020. An older 30-pint portable unit compares roughly with a newer 20-pint unit.
How Damp Is Your Apartment?
Put a hygrometer in the dampest room for at least 24 hours, away from direct steam, radiators, and open windows. The EPA advises keeping indoor relative humidity below 60%, ideally between 30% and 50%. A target around 45% to 50% is a practical starting point in damp rooms, as long as the air does not become uncomfortably dry.
- 30% to 50% RH: Good control for most homes.
- 50% to 60% RH: Watch closely and ventilate. Add a dehumidifier if condensation appears.
- Above 60% RH: Higher damp risk, especially on cold walls, window frames, and behind furniture.
- Musty smell, damp patches, or visible mould: Treat it as a moisture problem, not a comfort issue.
A simple four-step sizing rule
- Start at 10L for a small flat with light or seasonal condensation.
- Move to 12L if you dry laundry indoors, have more than two occupants, or damp returns most days.
- Consider 15L to 20L for a large open-plan flat or heavy laundry loads.
- Investigate the building if you see leaks, growing water stains, wet plaster, or spreading mould. A larger machine cannot repair a water source.
Temperature check: ENERGY STAR notes that frost can form on compressor coils below about 65°F (18°C). If the room is often that cold, check the manufacturer’s low-temperature operating range.
Should You Buy a 10L or 12L Dehumidifier?
Choose 10L if humidity usually stays below 60% and you mainly want to keep windows clear in colder months. It is compact and easy to move.
Choose 12L if damp comes back daily, you regularly dry washing indoors, your bathroom has poor extraction, or more than two people live in the flat.
If you are stuck between two sizes, ENERGY STAR advises that it is generally better to oversize than undersize, and a humidistat lets the unit cycle to your target humidity. Do not choose by the biggest number alone, since larger units can be heavier, louder, and harder to place in a small flat.
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Where to Place a Dehumidifier in a Flat
Put it where moisture builds up: near the bathroom door after showers, in the kitchen after cooking, beside an indoor clothes airer, or in a hallway that connects damp rooms. For whole-flat control, a central spot with internal doors open works if the manufacturer’s airflow requirements allow it.
- Keep the intake and outlet clear and follow the manufacturer’s clearances.
- Close outside windows and doors while it runs.
- Use extractor fans during and after showers and cooking.
- For laundry, use the smallest suitable room and leave space around the airer.
- Route any drain hose away from electrical cords and walkways.
- Move furniture slightly away from cold external walls so air can circulate.
Safety: Do not place a standard plug-in dehumidifier where it can be splashed by a bath or shower unless the manufacturer says it is safe there. Keep plugs and drainage water apart.
Features That Matter in an Apartment
- Humidistat: holds a target humidity automatically.
- Quiet operation: check the dB rating if you will use it near a bedroom or in an open-plan space.
- Laundry mode: useful if you dry clothes indoors.
- Continuous drainage: helpful for long run times.
- Auto shut-off: stops the unit when the bucket is full.
- Washable filter and a carry handle: easier upkeep and moving between rooms.
- Low-temperature operation: important for cool rooms and utility areas.
How Much Will It Cost to Run?
Running cost per hour = wattage ÷ 1,000 x your electricity unit rate per kWh. Ofgem lists an average electricity unit rate of 26.32p per kWh for Direct Debit customers in England, Scotland, and Wales from 1 October to 31 December 2026. Your own tariff may differ, and rates change each quarter.
| Power draw while running | Approximate cost per hour at 26.32p/kWh |
|---|---|
| 165W | About 4.3p |
| 250W | About 6.6p |
| 300W | About 7.9p |
These wattages are examples, not specific models. Check the rating label on the unit you are considering. Real cost depends on how often the compressor runs, so a humidistat, closed windows, a clean filter, and fixing moisture at the source all help keep it down.
When a Dehumidifier Is Not Enough
A dehumidifier removes moisture from the air. It does not repair leaks, blocked extractor fans, failed window seals, or water coming through a wall. Contact your landlord, building manager, or a qualified tradesperson if you notice:
- Water stains that grow after rain
- Wet plaster, bubbling paint, or crumbling skirting boards
- Mould spreading across walls or ceilings
- A musty smell that remains when humidity is controlled
- Condensation inside double-glazing panes
- Extractor fans that do not pull steam out of bathrooms or kitchens
If you rent, report leaks, failed fans, and recurring mould in writing.
Troubleshooting
- Humidity is not dropping: close windows, clean the filter, improve the position, and check for leaks.
- Tank fills very quickly: the moisture load is high. Check for leaks, wet laundry, poor extraction, or cold-wall condensation.
- Unit is noisy: make sure it sits level and use a quiet mode if available.
- Coils frost or output drops: the room may be too cold for that model.
- Air smells musty: empty and clean the tank, clean the filter, and inspect nearby walls and furniture for damp or mould.
Related guides
- What size dehumidifier do I need for a room?
- Bedroom dehumidifier size guide
- Bathroom dehumidifier size guide
- Do I need a dehumidifier in every room?
- Dehumidifier size for 2,000 square feet
Frequently Asked Questions
How big of a dehumidifier do I need for my apartment?
For many small apartments, start around 10L to 12L per day. A 10L model suits lighter condensation and modest moisture loads, while 12L gives more headroom for regular indoor laundry, more occupants, or persistent damp. Larger open-plan spaces or heavy moisture loads may need more capacity.
Is a 10L or 12L dehumidifier better for an apartment?
Choose 10L for a smaller flat with mild or seasonal condensation. Choose 12L if you regularly dry clothes indoors, have more than two occupants, or moisture returns most days. Layout, temperature, and your actual humidity reading matter too, so litres per day should not be the only factor.
What humidity should I set my apartment dehumidifier to?
The EPA advises keeping indoor relative humidity below 60% and ideally between 30% and 50%. A target around 45% to 50% is a practical starting point for many damp rooms, provided the air stays comfortable and you follow your model’s instructions.
Is a 10L dehumidifier enough for drying laundry indoors?
It can help with occasional laundry in a small room, but a 12L or larger unit gives more capacity if you dry clothes indoors often. Use an enclosed room, close external windows, space clothes apart, and use laundry mode if your model has one.
Should I leave a dehumidifier running all day?
Follow the manufacturer’s instructions. A humidistat lets the unit cycle to your target humidity, and auto shut-off or continuous drainage manages the water. If it runs almost nonstop without lowering humidity, check sizing, placement, temperature, ventilation, and possible water sources.
Sources
- ENERGY STAR: Dehumidifiers
- ENERGY STAR: Dehumidifier Testing and Capacity
- U.S. EPA: Mold Course, Chapter 2
- Ofgem: Energy price cap unit rates and standing charges
- Meaco: Which dehumidifier do I buy for a flat?
