Dehumidifier Buying Guide: Choosing the Right Size

By Home & Kitchen Appliances – Morphy Richards UK | Published: 2026-10-16

Category: Buying Guides

Use room size, moisture level, and temperature to pick the right dehumidifier capacity. A practical buying guide with decision rules and trade-offs.

Quick answer

Match dehumidifier capacity to the room's worst-case moisture load, not its average. For a single damp bedroom or small flat, a compact 10–12 litre unit usually suffices; for a whole flat or a cold, damp room, choose 16–20 litres. If the room drops below 15°C, a desiccant model outperforms a compressor. Always check the extraction rate at your typical UK room temperature, not just the headline litre figure.

Start with the moisture load, not the floor plan

Room size is only a rough starting point. The real driver is how much water enters the air each day: drying laundry indoors, a leaking gutter, a bathroom without an extractor fan, or a damp cellar wall. A 20 m² bedroom used for sleeping needs far less capacity than the same 20 m² used to dry washing. Before you buy, note whether the damp is seasonal (winter condensation) or year-round (rising damp), and whether the room is heated. A heated room holds more moisture, so the dehumidifier has to work harder to hit a target relative humidity. If you cannot identify the source, a higher-capacity unit gives you headroom, but it will not fix a structural problem.

How to read capacity figures honestly

Manufacturers quote extraction in litres per day, usually at 30°C and 80% relative humidity. UK homes are often 15–20°C and 60–70% RH, so real-world output is lower. A 20-litre unit might extract only 8–10 litres in a cool hallway. Use the quoted figure as a ranking tool, not a promise. Also check the tank size: a 2-litre tank on a 20-litre unit means emptying it several times a day at full output. Continuous drainage via a hose is worth having if you plan to run the unit for hours in a cellar or utility room.

Compressor vs desiccant: the temperature decision

Compressor dehumidifiers are cheaper to run in warm conditions and common in UK homes. Their performance falls off below about 15°C, and they can struggle in unheated garages or conservatories. Desiccant models use a rotating wheel and work down to near freezing, but they usually cost more and use more electricity per litre extracted. If your problem room is cold for much of the year, desiccant is the safer choice. If it is a heated living space, a compressor model is usually the better value.

Noise, placement, and running costs

Check the decibel rating if the unit will run in a bedroom or open-plan living area. Most compressor models sit around 40–50 dB; some quiet modes help, but fan noise is still audible at night. Leave at least 20 cm of clearance around the unit and keep doors and windows closed while it runs. Running costs depend on wattage and how long you run it. A 300 W unit used 8 hours a day is roughly 2.4 kWh per day; check your tariff to estimate the cost. A humidistat lets the unit switch off once it hits your target, which saves more than buying a larger unit you run constantly.

Where a dehumidifier fits in a wider home routine

A dehumidifier manages airborne moisture, but it does not replace ventilation or fixing leaks. Pair it with extractor fans in bathrooms and kitchens, and open windows briefly to exchange air when outdoor humidity is low. If you are already organising a kitchen or utility space for laundry drying, the same practical thinking applies to cookware and storage: choose tools that suit the job rather than the biggest option. For example, a heavy-duty carbon steel oven tray set handles everyday baking and roasting without warping, and a forged aluminium sauté pan gives even heat for stovetop cooking. These are separate purchases, but they follow the same rule: match the tool to the task and the space you actually have.

Decision rules for sizing a dehumidifier

Small single room, heated, occasional damp: Choose 10–12 litres per day with a 2-litre tank. Run it during laundry drying or after showers. If the room is above 18°C, a compressor model is fine.
Whole flat or multiple damp rooms: Choose 16–20 litres per day. Look for a humidistat and continuous drainage option. A larger tank or hose saves daily emptying.
Cold room, garage, or conservatory below 15°C: Choose a desiccant dehumidifier. Compressor performance drops in the cold. Accept higher running costs for reliable extraction.
Bedroom or open-plan living space: Prioritise a low decibel rating and a night mode over maximum capacity. Check the noise figure before buying, not after.

Product facts

13"x9" Oven Tray Set and Slotted and Solid Turner Set: 13"x9" oven tray set with heavy duty carbon steel and double coating non-stick. Durable and consistent heat distribution for baking, grilling, and roasting, with easy food release.
24cm Forged Aluminium Saute Pan - Cream: 24cm forged aluminium sauté pan with premium aluminium coating for non-stick performance. Generous size for everyday cooking and a durable construction that suits regular use.
Spare Illumination Kettle Spout Filter: Spare illumination kettle spout filter for models 108022, 108020, and 108021. A low-cost replacement that keeps your existing kettle working rather than replacing it.
Spare Frying Basket Handle: Spare frying basket handle compatible with model 482001. Restores a frying basket to full function with a simple install.