The one thing you need to know before buying a dehumidifier this autumn – and it'll make all the difference to how it tackles damp and condensation in your home

As condensation starts misting my windows and the laundry piles up faster than I can dry it, I start thinking about getting my dehumidifier out again.

If you're on the fence about investing in one of the best dehumidifiers, I can definitely vouch that they are quietly brilliant appliances that work away in the background, until you realise you've bought the wrong one.

Because if there's one thing you need to know before adding a dehumidifier to your home this season, it's that size and capacity matter far more than you might think. Not the physical size, but how much moisture the machine can extract in 24 hours (its capacity, measured can extract in 24 hours.

If you get it wrong, you could end up with a whirring box that never quite gets on top of the humidity or worse, one that costs more to run than it needs to.

So before you click add to basket, here's how to work out which capacity you actually need and why it makes all the difference once the heating's back on and the air outside turns chilly.

Why is dehumidifier capacity a key consideration?

When you see a dehumidifier labelled 10L or 20L, that doesn't refer to the tank size. It actually refers to the maximum amount of water it can pull from the air in a day under specific test conditions. Think of it as the unit's power rating.

Chris Michael, leading dehumidifier brand, Meaco's Chair, explains that 'the one thing to get right when buying a dehumidifier is capacity, but that goes hand in hand with low noise and energy efficiency.'

If your home is large or if you regularly dry laundry indoors, a small-capacity model will consistently run at full tilt and barely make a dent. Likewise, if you opt for one that's too powerful for a small bedroom, you'll be wasting energy and money. The trick is to match the extraction rate to room size and humidity levels.

'If the unit’s too small, it will run constantly and still leave the air damp. Too large, and you’ll waste energy,' adds Chris.

Chris Michael

Chris founded leading dehumidifier manufacturer Meaco and has been advising on humidity solutions and dehumidifiers since 1991 and is well-known within the dehumidifier industry across the world as a leader in innovation and sustainability. With a wealth of experience in the industry, Chris is committed to helping provide low-energy and low-noise solutions appliances that improve the lives of customers.

How to choose the right size dehumidifier for your home

Choosing the right size dehumidifier isn’t about guesswork; you should be looking to match the appliance with your home, explains Katie Lilywhite, dehumidifier expert at AO.com.

I've tested a fair few models over the years, and here's the general rule of thumb for choosing the right dehumidifier for your home, according to Chris:

• Small rooms or flats with light condensation: 10-12L
• Medium-sized spaces or regular laundry drying: 15L-20L (This SmartAir Dry Zone Dehumidifier works wonders in my house, £79.99, B&Q)
• Whole homes or heavy damp problems: 20L+ (I rate the Pro-Breeze 30L smart dehumidifier, RRP £229.99, Amazon)

'Essentially, if you choose a dehumidifier too small, then this unit will struggle, and should you go too big, then you’ll waste money on a dehumidifier that’s overkill for your needs,' explains Katie.

'Firstly, measure up the area you’re looking to treat. If your room is up to 15m², then you’ll need an 8-10L unit, whereas if you’re planning on using your dehumidifier in your living room (15–25m²), then you may need 12-16L. This jumps quite a bit to when you’re using your appliance in a large open-plan space – you’ll benefit from having a 20L+.'

Katie Lilywhite

AO's latest addition is Katie, a key expert at a multitude of appliances, including dehumidifiers, portable air conditioners, fans and air purifiers. 

What other conditions do you need to consider?

If your dehumidifier will live in a cool or unheated space, such as a garage or utility room, it's also worth choosing a dessicant model like the eBac 4650, £329. These work better in lower temperatures than compressor types.

And if you're drying clothes indoors, which most of us are in November, I'd always say go one size up. 'Opt for a bigger capacity dehumidifier or one with a dedicated laundry mode to get the most from your appliance,' adds Katie.

She also explains that if your home suffers from persistent damp, condensation or even mould, then you’ll need to try and get on top of this as quickly as you can. This is where you may need to choose a dehumidifier that is ‘larger’ than your home needs to tackle the problem head-on.

'If this problem is in a small room, then use a 12-16L dehumidifier like the MeacoDry Arete Two Dehumidifier 12L, £183.96, Amazon. Should it be in a medium-sized room, then you’ll want a 20L+ purely to pull the water out fast.'

The best dehumidifiers we've tested

Choosing the right dehumidifier isn't just about brand or features. It's more about matching the model to your home's moisture level. The smartest thing you to check before buying a dehumidifier this season is that the extraction capacity fits your space.

The right size will save you energy, protect your home from damp and condensation and make it far easier to stay comfortable all winter long.