The Ninja DoubleStack XXXL SL451 Smart is a 9.5 litre, two-drawer Air Fryer that can Max Crisp, Air Fry, Roast, Bake, Reheat, and Dehydrate. It’s a massive cooking space.
The two drawers can work as one or independently, using different modes, and the cooking computer can synchronise them to be ready at the same time. Presets for roast, along with its temperature probe, make it foolproof. Note, there is a model without the probe SL400WH.
And there is more. The two drawers come with a crisper plate and racks to allow you to cook DoubleStack in four ‘compartments’. It is ultra flexible.
What is Air Frying?
It has become the must-have device based mainly on the promise of healthier cooking than oil frying.
In reality, it is pretty much the same as a 200°C fan-forced oven, but uses a slotted basket to ensure a constant and even airflow around a smaller chamber. Many items don’t need oil, but most benefit from a light spray of canola oil (always use a low-smoke oil—not olive) or a tablespoon or two to brush or coat them.
The real issue is that air frying is not just for chips and junk food. It is fine for proteins you may have grilled or pan-fried, like chicken breasts/thighs/wings, burger patties, steaks, bacon, pork and lamb chops/cutlets, and sausages. They are all well-cooked, albeit lacking burnt grill marks that a hotplate provides.
This air fryer has twice the capacity of most, and its dual independent controls set it apart. It is perfect for large families.
Now I am going to segue
My indispensable daily cooking appliance is the Ninja AG551 Foodi Smart XL Grill & Air Fryer. I roast, bake, grill, air fry and reheat daily, and it is perfect for two people. It is a horizontal unit with a baking pan, grill plate and air fryer basket. It has presets and a temperature probe.
- Lamb, chicken, pork, beef roast and roast vegies to around 1kg – superb
- Grilled steak, pork, lamb, chicken or sausages
- Grilled cheese on toast and crisp store-bought croissants
- Heat convenience foods
It is somewhat of a serial cooking device in that you can do one thing at a time, albeit quickly. For example, a 500-600g lamb roast in 45 minutes, and while the meat is resting, it does the roast veggies perfectly. For comparison, we will call this Foodi.
The Ninja DoubleStack XXXL SL451 lacks the grill feature (that is invaluable), but it can cook much more, including meats and proteins at once.
Australian Review: Ninja DoubleStack XXXL SL451 Smart 9.5L 2 Drawer Air Fryer (prices as of 14/9/25)
| Website | Ninja Company site Product page Quick Start Owners Guide |
| Price | RRP $529.99 |
| From | Ninja Online, Harvey Norman, JB Hi-Fi, Good Guys, Bing Lee, Myer, Appliances Online |
| Warranty | 2-year ACL |
| Made in | China |
| Company | Ninja is a kitchen brand developed by SharkNinja, a pioneer in small household appliances and cleaning. Its headquarters are in Needham, Massachusetts, just outside of Boston. Mann&Noble is the exclusive distributor for SharkNinja in Australia, New Zealand, Singapore, and Malaysia. |
| More | I’mTech kitchen appliances news and reviews I’mTech Ninja news and reviews |
Ratings
We use the following ratings for many of the items below. I’mTech regards a score between 70 and 80/100 as a fit-for-purpose pass mark. You can click on most images to enlarge them.
- Fail (below expectations), and we will let you know if this affects its use.
- Pass(able) rating that is not as good as it should be.
- Pass (meets expectations).
- Pass ‘+’ rating to show it is good, but does not quite make it to Exceed
- Exceed (surpasses expectations or is the class leader).
First Impression – tall
It may take up less bench space at 286 W x 488 D x 385mm H x 10.8kg, but it is kind of monolithic and you need to leave room behind and at the side for air intake and in front to take out the draws – overall at least 800mm deep.
It is a 9.5-litre, two-drawer Air Fryer with two independent air fryer drawers, hence the name DoubleStack. It can Max Crisp, Air Fry, Roast, Bake, Reheat and Dehydrate (no grill plate or sear function).
Add all the Ninja smarts you have come to expect, and it can cook a lot at once.
Understanding experimentation
Cooking is all about experimentation. You will need to experiment with this, as it is like four foods on the go at the same time.
Cooks develop muscle memory for how long things take and at what temperature, be it in a Ninja DoubleStack XXXL or the Ninja Foodi XL Grill. What you need to remember is that each setting has recommended temperatures, but you may need to vary those.
- Air Fry: 150°C – 230°C (Max Crisp 240°)
- Roast: 120°C – 200°C
- Dehydrate: 27°C – 90°C
- Reheat: 150°C – 200°C
- Bake: 120°C – 200°C
We found that it was a different way to cook – not better or worse. Where we loved the Foodi for its horizontal pan, there are things you can do better in the DoubleStack.
If I were cooking for a family, the DoubleStack makes sense.
I want steak, chips, veggies and more.
We would typically do defrosted meats on the Foodie grill plate, which takes about 10 minutes to preheat. They then take about 3 minutes a side (medium rare) or 4 minutes (medium) and have those nice, grill-seared food marks. This is air frying and produces a different finish (more broiled) that you will either love or go back to a grill.
We tried Sirloin, pork cutlets, sausages, and chicken breast. The manual suggested meats on the top rack (it fits two 250-350g pieces) and veggies down below. It works, but the meat juices tend to drip onto the veggies. And we felt that the best results came from basting the meat.
Cooking was a little uneven as the heat came from the back of the basket, and we needed to rotate the food. Chips were in the second basket and required regular shaking.
My point is that using all four spaces will need planning and the right mix of proteins, starches and carbs.
Subjective rating: 7/10 for meats (Foodi 10/10)
Junk food – 9/10 mostly
We cooked a variety of junk foods all at once (all defrosted first, and no extra oil was used). Thanks to the wonderful people at Booker Bay Café for supplying these. If you are in the area, it has the best coffee and takeaway food on the Peninsula. The café would put these in the same oil deep fry basket for between 3 and 5 minutes.
The manual said that the crisper plate (lower) is best for vegetables, and the stacked rack is best for proteins and extra crispy.
The figures in brackets are the air fry cooking time.
- Chicko Roll (bottom – 10 minutes, hard exterior and not how you remember the greasy cabbage roll – this needs deep oil frying).
- Sav in batter (bottom – 10 minutes and superb crisp batter and cooked sav).
- Chicken Schnitzel (top – 2 x 5 minutes each side and 3 minutes for melted cheese on top. The basket fits two of these. Not quite as crisp as the Ninja Foodie does, and uneven cooking).
- Chicken Nuggets (10 minutes turned four times, and while tasty, the outer was drier than a deep fry).
- Crumbed Mozzarella sticks (top – 5 minutes, turn once and bursting with cheese).
- Chips (bottom – 20 minutes with frequent turning/shaking – not quite as fast as the Foodie but a similar outcome)
- Potato scallops (top -10 minutes, turn once)
- Hash Browns (top and bottom – 10 minutes, turn once and a bit dry).
The interesting item was the chips. Nicely done, but 20 minutes and frequent turning meant that items on the top shelf had to be removed.
Roast Lamb and roast veggies – Roast 9/10 and veggies 7/10
Our signature test is to roast a small 600g boneless lamb leg, two roast jacket potatoes, and the other roast vegetables in the other drawer. It should fit up to a 2kg chicken in each drawer.
The thermometer probe is only for the lower draw, and we selected Lamb and Medium. It would typically take 30-40 minutes in the Foodie roasting pan, and we would take it out and rest it for 20 minutes while the carrots and pumpkin are roasted in the meat juices. Those juices would then be used as the gravy starter.
Here, the trick is to program the top drawer for veggies first (Roast, 20 minutes) and the bottom drawer (Roast, Probe, Lamb, Medium), press Sync and away it goes.
Now experimentation is what this is all about, and the meat was perfectly cooked, and then started resting, and the vegetables should have been ready. Unfortunately, they were not and required about 10 more minutes. The carrots (bottom draw and drizzled with olive oil) were perfect, but the butternut pumpkin in the rack was dry and unappetising.
There was not enough pan juice to start the gravy. Foodi wins by a mile.
Support
It comes with a very comprehensive manual and guides for most meats and vegetables. You can search for a wide variety of recipes. Ninja Kitchen has lots of recipes, or search #NinjaDoubleStack #NinjaRecipes.
Maintenance and cleaning
While the drawers and racks are dishwasher safe, it’s easiest to wash them in the sink as they take up a lot of room.
The Foodie, with its low-profile basket, is easier to clean.
Power
The device is rated at 2270W.
- Roast: 230W
- Air Fry 512W
I’mTech’s insight: Ninja DoubleStack XXXL SL451 Smart 9.5L 2 Drawer Air Fryer for big appetites
I like Ninja for its variety of well-made cooking implements. It has a very strong brand loyalty.
The Ninja DoubleStack XXXL SL451 is not for everyone. It is more about 9.5 litres of space, double-stacked.
Although it has presets that may do most of it for you and matching and sync cooking, it requires a bit of thought to plan that meal using all four compartments. We wrecked, well overcooked, some nice steaks. Over four weeks, we finally learned how to try to get both baskets to cook in sync to deliver a meal at the same time.
And yet I have no such difficulty with my Ninja Foodi Grill that I can’t live without. I prefer the shallow and wider air frying basket, which I can do roasts and collect pan juices, and it is so quick from a cheese toastie to a full meal. But that is just me!
From our commercial kitchen tester
“We need volume and quick cooking. This meets both criteria”
- Flexible two separate draws and two racks
- Overcomes the problem of having two different food types to air fry, roast, etc., simultaneously.
- No pre-heat required – it reaches temperature very quickly.
- Logical controls are easy to use.
- You can mix and match programs at the same time.
- Use silicon tip tongs, etc., to preserve the basket finish.
- It is convenient for larger families as you can use one or both baskets.
- Well-made from a company that provides great user support.
- Lots of recipes online.
- Faster than expected (about 10% more than other Air Fryers we have tested).
- Not really for grilling (no grill plate) or baking (can’t use baking tins).
Ninja DoubleStack XXXL SL451 rating
While it has six functions, it’s more about 9.5 litres over four cooking areas, and that has a learning curve.
- Features: 85. Dual Drawer, dual controls, six modes, energy efficient.
- Value: 85. For what it is, this represents great value.
- Performance: 80. Air Fry food needs regular turning, so you may not be able to use the racks.
- Ease of Use: 75. Takes brain power to plan a meal using four spaces.
- Design: 80 – Well-made, 2-year warranty
