Most big family air fryers solve the capacity problem by getting wider. Two drawers side by side, a footprint like a microwave, and suddenly a third of your worktop has gone. Ninja’s Double Stack XL (model SL400UK) does it the other way round: it stacks the two drawers on top of each other, so you get 9.5 litres of cooking space in something only 28cm wide. If you’re feeding four or more people out of a small kitchen, that’s a genuinely interesting idea. It isn’t perfect, though, and some of the complaints from owners are worth hearing before you clear a space for it.

At a glance

  • What it is: a 9.5 litre, two-drawer air fryer with the drawers stacked vertically, plus two removable racks that turn it into four cooking levels
  • Footprint: 28cm wide, 47cm deep, 38.5cm tall, and it weighs 10.3kg
  • Best for: families or batch cooks who need dual-zone capacity but don’t have the width for a side-by-side model
  • Think twice if: your worktop is shallow, your wall cupboards sit low, or you mostly cook for one or two
  • Owner rating: 4.6 out of 5 from over 1,200 ratings on Amazon UK at the time of writing

What it actually does

Each drawer holds 4.75 litres, and each runs as its own cooking zone with its own fan at the back. That means you can do chicken in the top drawer at one temperature and chips in the bottom at another, then use the Sync button so both finish at the same moment. Match copies one drawer’s settings to the other, which is handy when you’re just doing a double batch of the same thing.

The racks are the clever bit. Each drawer comes with a crisper plate on the bottom and a meal rack that sits above it, so you can layer food inside a single drawer. Salmon fillets on the rack, broccoli underneath, that kind of thing. Ninja calls it four cooking levels, and it’s the reason the box claims it can make up to eight portions.

There are six functions: Max Crisp, Air Fry, Roast, Bake, Reheat and Dehydrate. Nothing exotic, but that covers almost everything people actually use an air fryer for. The drawers, crisper plates and racks are all dishwasher safe.

Why it suits a small kitchen

Width is usually what kills you in a narrow galley or a flat kitchen. Ninja says the Double Stack is 30% slimmer than its own Foodi MAX Dual Zone (the AF400), which has the same 9.5 litre capacity laid out side by side. On a run of worktop between a kettle and a hob, that difference is the gap between fitting and not fitting.

The trade-off is that it goes up and back instead. At 38.5cm tall it’ll sit under most wall cupboards, but you want some clear air above it, because hot air vents out of an air fryer and you don’t want that cooking the underside of a cupboard. Check the manual’s clearance guidance against your own kitchen before buying. And at 47cm deep it takes up most of a standard worktop front to back, so measure that too.

The good bits

  • Real family capacity in a narrow space. This is the whole point of it, and it delivers. Owners regularly mention cooking full roast dinners in it, including one who said it was used for Christmas dinner itself.
  • Two zones that finish together. Sync takes the mental maths out of getting a main and a side ready at once.
  • Solid build. A lot of positive reviews comment that it feels sturdy and well finished rather than flimsy.
  • Frozen food comes out properly crisp. One owner who’d written off air fryers as pointless said this was the one that changed their mind, nuggets and chips included.
  • Two year guarantee if you register it with Ninja (UK and Ireland).

The not so good bits

The critical reviews are a minority, but they cluster around a few themes, and they’re not trivial.

  • Some people find it slower than a standard dual-drawer Ninja. More than one owner coming from Ninja’s side-by-side models said this one takes longer to cook the same food, and one went as far as saying to buy the regular double drawer if you have room for it.
  • Layering takes a bit of learning. Pile too much onto the racks and the lower level doesn’t get enough airflow. A couple of disappointed reviewers said food wasn’t cooking through in the suggested times, which sounds a lot like overloading.
  • Reliability reports. A handful of owners describe the control dial or control board failing, in one case after a few weeks and in others after ten to eighteen months. That’s the minority experience, but it’s why registering for the guarantee matters.
  • The inside of the housing gets grubby. The drawers clean easily. The cavity they slide into, less so, and one reviewer also noticed the Ninja logo wearing off.
  • It’s heavy. 10.3kg isn’t something you’ll want to lift out of a cupboard every evening. Plan for it to live on the worktop.

Who it’s for (and who should skip it)

If there are four or more of you, you cook main-plus-side meals most nights, and your worktop is short on width rather than depth, this is one of the few dual-zone fryers that makes sense. Batch cooks will like the racks too.

If it’s just you, or you and one other person, it’s overkill. You’d be heating a big appliance to cook a small amount of food, and a compact single-drawer model will be quicker to clean and take up less room. Our Cosori 2L review and the best air fryers for one person are better places to start. And if you’ve got the width for a side-by-side model, it’s worth weighing those reports about cooking speed before you go for the stacked version.

How to get the best out of it

  • Give it an empty run before first use, with the window open. New heating elements often give off a smell for the first few heats (more on that in why air fryers smell like plastic).
  • Use the racks for things that cook evenly in a single layer, like fish, sausages or halved veg. Keep anything that needs shaking, like chips, on the bottom plate.
  • Don’t fill both levels of a drawer to the edges. Leave gaps so the air can get down to the bottom layer.
  • Expect to add a few minutes if you’re following timings written for a different air fryer, and check food is cooked through before serving, especially chicken.
  • Use Sync when the two drawers need different times, and Match for a straight double batch.

Cleaning and safety

Drawers, crisper plates and racks can go in the dishwasher, but hand washing with a soft sponge will keep the non-stick coating going longer. Skip anything abrasive (our guide to cleaning an air fryer basket without scratching it covers what works). Once it’s unplugged and cool, wipe out the cavity regularly with a damp cloth, because that’s the part owners say gets dirty fastest.

The safety basics are the same as any air fryer. Keep the vents clear, keep it away from the edge of the worktop and out of reach of children, and don’t use it under a cupboard that leaves no room for heat to escape. Because the drawers pull out at two different heights, take a bit of care with the top one when it’s full of hot oil from roasting.

FAQ

Can you cook two different foods at once?
Yes. Each drawer has its own temperature and timer, and Sync makes them finish together.

Is it louder than a normal air fryer?
There are two fans, one for each drawer, but noise isn’t one of the recurring complaints in the reviews. It sounds like any air fryer running.

Will it fit under my kitchen cupboards?
At 38.5cm tall it fits under most, but leave space above it for heat to escape and check the manual’s clearance advice first. Depth (47cm) is worth checking too.

What’s the difference between this and the smaller Double Stack?
Ninja also sells a 7.6 litre Double Stack (SL300UK). The XL is the 9.5 litre version, aimed at bigger households.

Is it good for a single person?
Not really. It’ll work, but you’re paying in space and cleaning for capacity you won’t use. A compact single-drawer fryer suits one person better.

The verdict

The Double Stack XL is a smart answer to a real problem: how to get family-sized, two-zone air frying into a kitchen that doesn’t have the width for it. Most owners love it, and the stacked design really does save worktop space. Go in knowing it can be a little slower than Ninja’s side-by-side models, that the racks reward a light hand, and that a minority of units have had control problems. Measure your depth and cupboard height first, register the guarantee, and it should earn its spot.

Check the current listing on Amazon UK: Ninja Double Stack XL 9.5L Air Fryer (SL400UK)