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Stacking its dual drawers on top of each other, the Ninja Double Stack XL 9.5L Air Fryer SL400UK offers a staggering 9.5 litres of cooking space squeezed into a device that only takes up the same counter space as a singe-zone air fryer. New to this model is dual-layer cooking, so you can cook four different things at once, with the slight caveat that it can be fiddly to turn food during cooking. That minor issue aside, brilliant results and intuitive controls make this my favourite dual-basket air fryer.


  • Excellent results
  • Huge amount of cooking controls
  • Brilliant controls


  • Can be fiddly to turn food with dual-layer cooking

Key Features

  • Cooking spaceThere’s a total of 9.5-litres of space, split evenly between the two 4.75-litre drawers.
  • Cooking modesMax crisp, air fry, roast, bake, reheat and dehydrate modes are available in both drawers. When using both drawers you can run them separately, match the settings or use sync to have two different functions finish at the same time.


I love the convenience of a double-drawer air fryer, but the counter space they take up makes them a no-go for many people. With the Ninja Double Stack XL 9.5L Air Fryer SL400UK, you get two drawers, one stacked on top of the other, so the air fryer only takes up the same footprint as a single-drawer model.

With two-layer cooking added into the mix, high temperature cooking and excellent results across the board, this is the best dual-drawer air fryer yet.

Design and features

  • Vertical arrangement saves on counter space
  • Dual-layer cooking
  • Max Crisp mode

The Ninja Foodi MAX Dual Zone Air Fryer AF400UK showed the power of dual-drawer air fryers, but it’s one heck of a beast, taking up a lot of counter space. With the Ninja Double Stack XL 9.5L Air Fryer SL400UK, you get the same 9.5-litre capacity (4.75-litres per drawer), with the unit taking up just over half the counter space by comparison.

Impressively, although the Double Stack is taller than the AF400UK, it’s only taller by 6cm, so doesn’t look dominating.

Stacking the drawers vertically, Ninja has had to redesign the system’s workings. Rather than having the heating element and fan at the top of the drawers, as with the AF400UK, they have been relocated to the back of the unit, blowing through the vents in the back of the drawers.

That redesign has one additional benefit: each drawer can cook on two layers with the provided wire racks. For multi-layer cooking, the Double Stack Pro button needs to be hit, and anything on the wire rack needs to be large enough not to fall through the gap.

Ninja Double Stack XL 9.5L Air Fryer SL400UK drawer
Image Credit (Trusted Reviews)

That aside, two-layer cooking lets you double up on capacity, or even cook an entire meal in just a single drawer.

There are a couple of drawbacks to this cooking system. First, two-layer cooking works best if your layers cook at the same temperature for the same amount of time; if you’ve got a mismatch, as I had, then you’ll need to add one layer part-way through the cook.

Secondly, turning food becomes much harder. While the wire racks have handles, so you can lift them out with oven gloves, doing so while they’re loaded with food isn’t always practical.

That’s not to say that I don’t appreciate the dual-layer cooking; it’s just that the mode needs to be used with full awareness of its caveats to get the best results.

Without the wire racks, each drawer features a standard 4.75-litre capacity, with a crisper plate at the bottom. A handle on the front makes it easy to remove a drawer and shake food to help it cook evenly.

Ninja has once again demonstrated that it’s the master of interface. Rather than having a complex array of modes designed for specific foods, such as chips and chicken, the controls consist of the mode (Air Fry, Roast, Max Crisp, Reheat, Bake and Dehydrate), temperature and time. Max Crisp doesn’t have temperature selection and runs at 240°C, with just the time selectable; it’s designed for foods that need a really crispy finish such as hash browns.

Ninja Double Stack XL 9.5L Air Fryer SL400UK main controls
Image Credit (Trusted Reviews)

Ninja provides a useful booklet with suggested modes, temperatures and cooking times for most common foods, which makes life easier. Overall, the Double Stack is lightning-quick to use.

Drawers can be used individually, effectively giving you two separate air fryers. However, the drawers can be used together. Match mode sets both drawers to the same settings which is useful when you want to double up on the same ingredients.

Sync mode lets you cook on different settings, but the drawers are automatically timed to finish simultaneously. The Ninja Double Stack XL 9.5L Air Fryer SL400UK is designed in such a way that achieving what you want is easy.

Ninja Double Stack XL 9.5L Air Fryer SL400UK Dual Drawer controls
Image Credit (Trusted Reviews)

Drawers and accessories are dishwasher safe, although they’re almost as quick and easy to wash by hand.


  • Very crispy results
  • Two-layer cooking is effective
  • Excellent cooking

I started by cooking a batch of oven chips along with some fish fingers, using the two-layer cooking mode. As the fish fingers require less cooking time than the chips, I added these a few minutes into the cooking process.

Ninja Double Stack XL 9.5L Air Fryer SL400UK dual-layer cooking
Image Credit (Trusted Reviews)

At the end of cooking, my chips were perfectly and evenly cooked, and the fish fingers had a nice crisp finish to them. You can’t do better than that, and being able to use one drawer for a complete meal is brilliant.

Ninja Double Stack XL 9.5L Air Fryer SL400UK chips
Image Credit (Trusted Reviews)

Next, I used the Max Crisp mode for hash browns, cooking them from frozen in just 12 minutes. The results are incredible, with a super-crispy exterior and a fluffy interior that rival air fryers can’t match.

Ninja Double Stack XL 9.5L Air Fryer SL400UK hash browns
Image Credit (Trusted Reviews)

I also cooked an entire chicken on the roast setting. Fitting a chicken into a drawer means I could cook an entire family-sized meal in just one air fryer.

Ninja Double Stack XL 9.5L Air Fryer SL400UK chicken in a drawer
Image Credit (Trusted Reviews)

Cooking in just an hour, I used a temperature probe to make sure that the chicken was cooked through (it was). I was impressed with the results: the skin was very crispy while the chicken remained moist inside.

Ninja Double Stack XL 9.5L Air Fryer SL400UK chicken
Image Credit (Trusted Reviews)

I used the dehydrate mode on apple slices, to remove the moisture content. They make a neat snack that will last longer than fresh slices. I also find dehydrate a useful option for garden herbs.

Ninja Double Stack XL 9.5L Air Fryer SL400UK dehydrated apples
Image Credit (Trusted Reviews)

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Should you buy it?

You should buy if you want big capacity but have limited counter space

Vertical alignment of the drawers means you get a lot of cooking space but save on counter space.

You should not buy if you want different features

If you want a grill, steaming or other cooking options then a different type of air fryer may be for you.

Final Thoughts

In all ways, the Ninja Double Stack XL 9.5L Air Fryer SL400UK is a better choice than the older AF400UK. The Double Stack has the same capacity but takes up less counter space and adds dual-zone cooking, to expand capacity even further.

Overall, the results from the Double Stack are exceptional and it’s the most useful dual-drawer air fryer that I’ve tested. Needs differ, and the AF500UK with its dividable large drawer is better if you just need massive capacity, while the Ninja Speedi gives you a steam mode and dual-layer cooking for meals in 15 minutes for additional versatility. Check out our guide to the best air fryers for other options.

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How we test

We test every air fryer we review thoroughly over an extended period of time. We use industry standard tests to compare features properly. We’ll always tell you what we find. We never, ever, accept money to review a product.

Find out more about how we test in our ethics policy.

Used as our main air fryer for the review period

We cook real food in each air fryer, making chips, frying sausages and cooking frozen hash browns. This lets us compare quality between each air fryer that we test.


How does two-layer cooking work on the Ninja Double Stack XL 9.5L Air Fryer SL400UK?

Using the wire rack, a drawer can hold one layer of food on the crisper plate and another on the rack, doubling up on capacity.

Full specs

Size (Dimensions)
Release Date
First Reviewed Date
Model Number
Stated Power
Number of compartments
Cooking modes
Total food capacity

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