How to Choose a Dehumidifier: 12L vs 20L Size Guide

The choice between a 12L and 20L dehumidifier is rarely academic — for UK homeowners wrestling with condensation and damp laundry rooms, it is the difference between a machine that quietly solves the problem and one that struggles uselessly in a wet corner while mould creeps up the walls. A properly sized unit can cut laundry drying costs dramatically, while an undersized model wastes both money and effort.

Recommended for larger homes: 20L capacity · Energy-efficient pick: MeacoDry Arete Two · Key factor: Room size and dampness · Common comparison: 12L vs 20L · UK expert tip: Martin Lewis on savings

These key specifications summarise the main trade-offs covered in this guide.

How do I determine what size dehumidifier I need?

Three things drive the right size: the room’s square footage, how damp the space actually is, and what you plan to use the machine for. A laundry room in a 3-bedroom end terrace with a history of condensation calls for something different than a spare bedroom that only gets stuffy in summer.

Factors like room size and dampness

The “size” on a dehumidifier is not the machine’s physical dimensions — it is the daily water extraction rate in litres per day (L/day), as confirmed by AirCon Centre, a specialist UK retailer. A higher litre rating means the unit can pull more moisture from the air each day, making it suitable for larger or wetter spaces. Tank capacity — the actual water container — is typically 2–6L and is a separate spec, as B&Q’s buying guide notes. Think of it like a car’s fuel tank versus its engine power: the tank holds what you have extracted; the extraction rate determines how fast you fill it.

Dehumidifier size calculator basics

Pro Breeze, a specialist manufacturer, offers a straightforward square-footage guide:

• 300 sq ft with severe damp → 12L/day
• 500 sq ft with drenched conditions → 16L/day
• Larger spaces → 20L/day

The AirCon Centre breaks it down by UK bedroom count and dampness level:

• Slightly damp 3-bedroom single-storey home → 12L recommended
• Wet conditions in a 3-bedroom home → 20L recommended

Sizing for a 3 bedroom house

For a typical 3-bedroom house in the UK, the right answer depends entirely on your dampness level. A slightly damp, well-ventilated 3-bedroom home can get by with a 12L model. If you have persistent condensation on windows, damp walls, or a perpetually damp utility room, the 20L is the safer recommendation. MoneySavingExpert forum users actively debate this exact scenario — owners of 3-bedroom end terraces with laundry damp argue over whether the 12L Meaco Arete One is enough or whether they need to step up to 20L.

Which is better, a 12L or 20L dehumidifier?

The honest answer: it depends on what you need the machine to do. These two capacities serve genuinely different use cases, and choosing wrong means either fighting a losing battle against damp or paying for power you do not use.

Power and capacity differences

Pro Breeze notes that domestic dehumidifiers range from 0.25L to 20L extraction capacity. The 12L models handle moderate damp conditions effectively — they pull around 12 litres of water from the air per day and are typically sufficient for small-to-medium rooms with slight-to-moderate humidity, according to AirCon Centre. The 20L models target homes with severe humidity issues, according to The Independent. The pattern is clear: size up when dampness is persistent and spaces are large; size down when the problem is occasional condensation or laundry drying.

Meaco Arete 12L vs Probreeze 20L

The Independent’s tested examples show a 12L model runs at 36–39dB — comparable to a quiet conversation — with a 160W consumption and a 3.5L tank. Energy-efficient 20L models like the Duux Bora Smart, also praised by The Independent, cost only 3p per hour to run — an unexpectedly competitive figure. Ideal Home cites a 200W model costing 7p per hour at a slightly higher electricity rate of 34p/kWh.

Energy use comparison

Running cost is where the practical difference lands. A 200W dehumidifier costs roughly 6p per hour at the January 2026 electricity rate of 28p/kWh, as The Independent reports. For context, Netmums notes the Meaco Arete One 10L costs just 4p per hour to run. Dehumidifiers typically run for 30p per hour or less — far cheaper than a tumble dryer, which Martin Lewis labelled a “demon appliance” in 2023 due to running costs that can reach up to £1 per hour, as The Independent reports.

This comparison illustrates why capacity and efficiency matter in tandem.

How do I figure which dehumidifier is best for my house?

Buying a dehumidifier is less about chasing a brand and more about answering three questions honestly: how big is your space, how damp does it get, and how often will you run the machine?

Types and features to consider

Dehumidifiers work by pulling moist air across a cooling coil (compressor models) or a rotating desiccant wheel (desiccant models). Compressor models are more energy-efficient in warm rooms; desiccant models perform better in colder spaces. Most UK buyers opt for compressor models for standard living spaces. Beyond the core mechanism, look for auto shut-off when the tank is full, a continuous drain hose option for the 20L machines used in persistently damp rooms, and laundry mode for drying clothes, which The Independent confirms shortens drying time by pulling moisture directly from the air.

Efficiency and energy savings

AirCon Centre confirms that larger extraction units handle bigger spaces and higher moisture more effectively. The B&Q guide notes that a 3.5L tank is suitable for everyday use without frequent emptying. For energy savings, the key metric is wattage. Martin Lewis breaks it down simply: a 200W unit draws one-fifth of a kilowatt, which at 28p/kWh translates to roughly 6p per hour, as The Independent reports. Lower wattage means lower running costs — prioritising efficiency over the purchase price pays back over months of use.

Best for whole house use

AirCon Centre recommends a 20L unit for wet conditions in a 3-bedroom home. Users on the MoneySavingExpert Forum debate whether a 12L can cover a 3-bedroom end terrace or whether 20L is essential for whole-house use. The practical answer: a 20L unit is better placed to handle the combined moisture load of multiple rooms and larger ceiling heights. A 12L can work whole-house only if you move it between rooms and close internal doors to target one space at a time.

What did Martin Lewis say about dehumidifiers?

In 2023, Martin Lewis labelled tumble dryers a “demon appliance” — calling out their running costs that can reach up to £1 per hour. The context is stark: according to The Independent, dehumidifiers typically run for 30p per hour or less. That single comparison has driven thousands of UK households to reconsider how they dry their clothes.

Savings on energy bills

Martin Lewis does not simply make the claim — he walks through the calculation himself:

“Once we know it’s 200W and we know a kilowatt is 1,000W, which is how electricity tends to be priced, we know this is a fifth of a kilowatt.”

— Martin Lewis, MoneySavingExpert founder (The Independent)

His practical application: at the January 2026 electricity rate of 28p/kWh, a 200W dehumidifier costs roughly 6p per hour. Ideal Home puts it at 7p per hour at 34p/kWh — and points out that this is running a dehumidifier continuously, not just for laundry drying.

“Dehumidifiers take water out of the air rather than use the heating and they’re much lower wattage appliances than standard heating.”

— Martin Lewis, MoneySavingExpert founder (Netmums)

Recommendations for budget models

Martin Lewis’s energy advice focuses on wattage as the primary cost driver rather than brand. Netmums reports on his practical approach: pick the dehumidifier that solves your condensation problem, not the most expensive model on the shelf. The Meaco Arete One 10L costs around £159.99 and runs at 4p per hour, according to Netmums. This is a solid budget-friendly entry point — and for persistently damp homes, stepping up to a 20L model from the same brand line makes sense.

Aldi dehumidifier backing

Martin Lewis has also backed Aldi’s budget dehumidifier as a cost-effective option for homes watching energy bills. His broader message: the upfront price is secondary to the running cost over months of use. A machine that costs £50 more to buy but runs at 3p per hour instead of 6p per hour pays back that difference within weeks of regular laundry drying.

“You’re going to pay roughly 7p per hour to run a dehumidifier at 200W, assuming it uses full power the whole time.”

— Martin Lewis, MoneySavingExpert founder (Ideal Home)

When not to use a dehumidifier?

Dehumidifiers are not a universal fix. There are situations where they are the wrong tool — or where they need to be used alongside other measures rather than alone.

Health conditions like COPD

If you or someone in your household has COPD, asthma, or another respiratory condition, run a dehumidifier only on medical advice. The machine increases air circulation and changes room humidity — which can affect breathing comfort for sensitive individuals. This is not a reason to panic, but it is a reason to check with a GP or respiratory specialist before committing to full-time use, particularly in bedrooms.

Overly dry environments

In well-ventilated older properties with good airflow, a dehumidifier may struggle to find enough moisture to justify its running cost. Netmums notes that dehumidifiers are not a fix for structural damp — if condensation keeps returning despite regular dehumidifier use, the issue may be rising damp or penetrating damp that needs a professional building survey, not a household appliance.

“Dehumidifiers take water out of the air rather than use the heating and they’re much lower wattage appliances than standard heating.”

— Martin Lewis, MoneySavingExpert founder (Netmums)

Maintenance tips

Dehumidifiers need basic maintenance to perform reliably. Empty the tank regularly — a machine running continuously with a full tank will shut off automatically and leave moisture unresolved. Pro Breeze’s guide recommends cleaning the filter every few weeks to maintain airflow. If your model has a continuous drain hose, make sure it is correctly positioned to drain into a floor waste or sink. Skipping maintenance is the most common reason a dehumidifier underperforms — not a wrong size choice.

Steps to choose and buy the right dehumidifier

Follow these five steps before buying:

1. Measure the room’s square footage and note the dampness level (slight, moderate, wet, or drenched)
2. Match extraction capacity: 12L for moderate damp up to 500 sq ft; 20L for wet conditions in larger spaces
3. Prioritise energy efficiency — lower wattage means lower running costs, and savings compound over months of use
4. Check practical specs: noise level (36–39dB is quiet), tank size (3.5L+ for daily use), and auto shut-off
5. Decide whether you need smart scheduling, continuous drain, or laundry mode for your specific use case

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