Narwal Flow 2 Review: Long Runtime, Odd Decisions

Narwal has steadily made a name for itself in floor care with capable products, and robot vacuums remain the core of the Chinese manufacturer's business. The Flow 2 is one of the most recent models off the production line, and it brings an avalanche of technology, headed by a quoted suction figure of 31,000 Pa.

There is also an anti-tangle system for the brush, a mopping roller that extends sideways to reach otherwise inaccessible corners, and detailed visual detection of dirt. Maintenance is meant to be largely automated: the base empties the mobile unit and refills its tanks when it returns, washes the roller with hot water quoted between 45 °C and 100 °C, then dries it at 60 °C.

The slightly rounded base of the original Flow has had its day. Its successor prefers a much squarer look, though the result is ultimately fairly sober, and a light bar above the robot's parking space adds a small futuristic touch.

The robot itself is relatively discreet, dressed in anthracite and black with a few chrome accents. Like the vast majority of robot vacuums it is circular, a shape intended to cover ground as efficiently as possible, and a set of buttons on the top surface pauses it or sends it back to its base. Very conventional, in other words.

Installing the base, its ramp and the power connection poses no problem, but Narwal has taken mischievous pleasure in scattering stickers, covers and transport locks more or less everywhere on the robot. Removing every one of them before the Flow 2 is run for the first time is essential.

The Narwal app has changed little since the first Flow. Pairing causes no particular difficulty, and once the Flow 2 has mapped its working area, and the map remains as precise as ever, the detailed work can begin.

The user starts by choosing between a complete clean of the home or a specific zone, adjusting the size and shape of a rectangle. A free-hand outline of that zone would probably have been more precise around walls and furniture, but this is more than enough for day-to-day use.

The different job types, vacuuming and mopping together or either on its own, are all present, and their intensity can be adjusted. For anyone who would rather not bother with any of that, the Freo mode promises to handle the configuration automatically according to how dirty the floor is.

The application holds plenty of other functions, from the genuinely useful, such as map customisation, weekly scheduling and mop humidity levels, to the marginal, such as the behaviour of the base's LEDs or a live view of what the robot's camera is filming. Instructions seemed clear, although a few translation errors intrude on the experience.

Session history is still part of the package, as is remote use of the base's functions: emptying the dust bag, disinfecting the bag and the mops, and so on. In short, the app has barely evolved, and that is no bad thing, because it was already comprehensive and intuitive.

The point of a robot vacuum is to free the user from housework, and the ideal is to keep maintenance to a minimum as well. On that score the Flow 2's base is reasonably well thought out. It stores the debris collected by the mobile unit, which returns mid-clean to empty its bin whenever it fills up, an entirely standard arrangement that few serious robot vacuums do without.

It would have been welcome if the Flow 2 had dispensed with dust bags altogether, as Dyson has with its Spot&Scrub AI, but that is not the case. Owners therefore have to live with consumables that remain awkward to dispose of, built as they are from paper, hard plastic and rubber, all glued together.

Rather unusually, the clean and dirty water tanks are directly accessible; no lid has to be lifted to remove them or slot them back into place. Filling and emptying are easier as a result, but replacing the dust bag suffers. It sits at the bottom of a flap underneath the two tanks, and that flap has to be closed again before the tanks can go back. Another small problem appeared during testing: the part of the bag that slots into a groove to seal it is sometimes not properly engaged, without the app warning the user. Caution is advised on that point.

Maintenance on the mobile unit is not complicated, although extracting the small dust bin occasionally calls for delicate fingers and a blacksmith's grip at the same time. Narwal has made a great deal of its anti-tangle system for long hair, perhaps prematurely, since long threads were frequently found wound around the roller. The roller does at least come out of its housing without difficulty, and without tools, so those threads can be removed.

The Flow 2 is less discreet than its predecessor. In normal vacuuming mode a sound-level meter recorded 52 dB(A), rising to a peak of 64 dB(A) in the most powerful setting. It is worth bearing in mind that a machine of this kind is designed to work when nobody is at home.

As noted above, the map produced by the Flow 2 is fairly precise and the rooms of a home are easily recognisable, which is the prelude to any decent navigation.

The robot passes a little further from obstacles than is ideal, even though it manages better than many comparable machines. A cable, a tea towel and a sock all give it pause, whereas it moves confidently around a shoe, and chair legs and the space beneath a chair cause it no trouble at all.

Its handling of the architecture of a room invites more scepticism. It does reasonably well against skirting boards, but has more difficulty reaching the corners of rooms and protruding angles. When set to vacuum a predefined zone it also wanders off to work elsewhere from time to time, for reasons that are hard to fathom.

The algorithm's interpretation of what the camera sees is another weak point. The twenty or so grams of chocolate powder used for the filtration test were treated as a new rug, and, not having been configured for it, the Flow 2 carefully avoided the chocolate-covered area, which is unhelpful for anyone coming home in the expectation that the cleaning has been done.

With a great deal of persistence, the Flow 2 does climb the small step of the grooved test board, a fairly rare feat that deserves recognition, and its refusal to give up before succeeding is admirable. The original Flow seemed better at the exercise, though: the Flow 2 spent a good quarter of an hour butting against the step before hauling itself up, only to come back down twenty seconds later and struggle just as much on the next attempt.

Despite a lack of raw power that stops it shining on old parquet with gaps between the boards, the Flow 2 posts attractive vacuuming results. On long-pile carpet it collected 86 per cent of the debris in normal mode and 90 per cent at maximum power. Thin carpet is handled effectively too, with only 5 per cent of debris remaining after a pass in normal mode and 4 per cent at maximum power. On hard floors the figures reach 99 per cent in normal mode and 100 per cent in the intensive setting.

It appears, however, that the roller is doing most of the work. Suction alone lifted just 2 per cent of the fine dust from the test groove in normal mode. Results improve at maximum power, at 6 per cent, but there is not a great deal to celebrate there.

The Flow 2's failing is an eagerness to do too well. Its layout allows it to clean into corners and reach marks that collect there, while the edges along skirting boards are less well cleaned, which is a little odd.

On raw performance, the Flow 2 can do nothing about wax crayon, which is hardly a black mark given how stubborn that soiling is. It is far more effective on the ketchup mark, and oil and fizzy drink also come up very well, but with a substantial caveat.

During testing those two marks were classed as liquid spills, even though the spillages were nothing like torrential and every other robot in the same comparison, including the original Flow, had treated similar accidents as perfectly ordinary soiling. The Flow 2 then set about applying what the application calls an intelligent change of cleaning strategy. The result was that it took the robot more than half an hour to clean a few drops of fizzy drink and a little oil, alternating far too many superfluous passes with returns to base to wash the roller and take on clean water. Interminable is the word. The two marks did come up, but rivals reach a comparable result in roughly a tenth of the time.

If the Flow 2 is persistent, it is also genuinely enduring. It can vacuum for five hours in normal mode before returning to base to charge back to 100 per cent, an operation that requires four hours of patience. In the most powerful mode endurance falls, but still reaches three hours.

Competition is fierce. The Dyson Spot&Scrub AI is one, with the advantage of doing without dust bags. The Mova P70 Pro Ultra is another highly recommendable option.