Ninja DoubleStack XL 9.5L (SL451UK / SL400UK)

Ninja DoubleStack XL 9.5L Review: Vertical Air Fryer with Smart Thermometer Power

In-depth review of the Ninja DoubleStack XL 9.5L Air Fryer (SL451UK / SL400UK). Explore its vertical design, smart thermometer, 6 cooking modes, and dual-drawer capacity.

The Ninja DoubleStack XL 9.5L is the vertical air fryer taken to the next level. With a full 9.5 litres of cooking capacity split across two stacked drawers, this model — SL451UK / SL400UK — packs in 6 versatile cooking functions and an integrated smart thermometer. Designed to save counter space while still serving full family meals, this is Ninja’s most space-efficient high-capacity air fryer yet. It's perfect for households who want serious cooking power without losing half their kitchen surface.

What Is the Ninja DoubleStack XL Air Fryer?

The Ninja DoubleStack XL is a vertically-stacked air fryer with two extra-large drawers — each with 4.75L capacity — offering a total of 9.5L cooking volume. It features 6 cooking functions: Air Fry, Max Crisp, Roast, Bake, Reheat, and Dehydrate. The standout addition is the integrated smart thermometer, which enables real-time cooking precision for proteins like chicken, steak, and fish. Its upright design means it fits better in tight kitchens while delivering all the performance of a premium dual-zone model.

Key Features of the Ninja DoubleStack XL 9.5L

  • 📏 9.5L Total Capacity: Two 4.75L drawers, ideal for family-sized portions or meal prepping.
  • 📡 Integrated Smart Thermometer: Monitors internal meat temperature and auto-adjusts settings for perfect doneness.
  • 🔥 6-in-1 Cooking Functions: Air Fry, Max Crisp, Roast, Bake, Reheat, Dehydrate.
  • 🔀 Sync Cook & Match Cook: Cook two different dishes or mirror settings for big batches.
  • Vertical DoubleDrawer Design: Saves horizontal counter space, stands tall at ~45cm.
  • 2470W High Power Output: Rapid heat-up and even cooking across both zones.

Design & Build of the DoubleStack XL

The DoubleStack XL is tall, sleek, and practical. It uses a matte black finish with chrome handles, and a central display that separates the two drawers. Each drawer is solidly built with a smooth pull, non-stick interior, and dishwasher-safe crisper plates. The thermometer stores neatly on the unit and connects magnetically. Its compact width makes it a better choice for UK kitchens where worktop space is limited but vertical space is available.

Capacity and Dimensions of the SL451UK / SL400UK

This air fryer offers 9.5L total capacity — each basket holds 4.75L, making it one of the largest vertical models on the market. Great for cooking two full meals side by side, from salmon fillets and asparagus to roast chicken thighs and crispy potatoes. Despite the generous capacity, the footprint is surprisingly compact at ~28cm wide and 45cm tall. It's ideal for families who want volume but can’t spare a wide footprint.

Cooking Results and Speed

The 2470W power output translates into rapid heating and reliable cooking across both baskets. Max Crisp mode handles frozen food like a pro, delivering restaurant-style chips in under 20 minutes. The smart thermometer makes chicken breasts and steaks easier than ever — once the internal temp hits your selected doneness, the fryer stops cooking automatically. Roast and Bake settings work well for both meat and sweet treats like muffins or banana bread. You can also dehydrate fruit in small batches across both drawers.

Ease of Use and Smart Features

The 2470W power output translates into rapid heating and reliable cooking across both baskets. Max Crisp mode handles frozen food like a pro, delivering restaurant-style chips in under 20 minutes. The smart thermometer makes chicken breasts and steaks easier than ever — once the internal temp hits your selected doneness, the fryer stops cooking automatically. Roast and Bake settings work well for both meat and sweet treats like muffins or banana bread. You can also dehydrate fruit in small batches across both drawers.

Cleaning the Ninja DoubleStack XL

Thanks to non-stick coatings and removable crisper plates, cleaning is fast and stress-free. Both baskets are dishwasher safe, and the central control panel wipes clean with a damp cloth. The smart thermometer is waterproof (probe only) and easy to clean with a sponge. Just be sure to cool the unit fully before deep cleaning.

Where to Buy the DoubleStack XL (UK)

Available at NinjaKitchen.co.uk and promoted in publications like The Sun, the DoubleStack XL typically retails for £199–£229. Stock can vary due to high demand. Look for seasonal offers that bundle the thermometer and accessories for added value.

Pros and Cons of the DoubleStack XL

  • ✅ Dual drawers with 9.5L capacity
  • ✅ Integrated thermometer for protein accuracy
  • ✅ Vertical design saves space
  • ❌ Tall height may not fit under all wall cabinets
  • ❌ Premium price vs standard dual-zone models

How the DoubleStack XL Compares to Other Ninja Air Fryers

Compared to the SL300UK, the DoubleStack XL offers significantly more capacity and includes the integrated thermometer. It’s closer in performance to the AF400UK but occupies less horizontal space. If you want advanced features without the wide design of traditional dual air fryers, this is your upgrade path.

Final Verdict on the DoubleStack XL 9.5L

The Ninja DoubleStack XL combines everything people love about Ninja’s dual-drawer technology — flexibility, power, crisp results — into a smarter vertical format with bonus tech. It’s ideal for families who want fast, flavourful food but need to optimise for space. The smart thermometer is a standout feature, and combined with the large drawers, this model earns its place as one of Ninja’s most practical and powerful options yet.

Ninja DoubleStack XL FAQs

Is the smart thermometer removable?

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Yes — it’s built-in but detaches for cleaning and storage. It magnetically clicks into the drawer housing.

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How much vertical space does it need?

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It’s about 45cm tall, so check clearance under cabinets or shelves if placing near a wall.

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Can I bake in both drawers at once?

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Yes — both drawers can bake independently, making this great for batch baking or cooking savoury and sweet together.

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Is it worth upgrading from the SL300UK?

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If you cook for more people or want the thermometer precision, yes — it’s a worthy upgrade.

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Best Recipes for the DoubleStack XL