Air Watts, Water Lift & Air Flow, what do they mean?

Air Watts

In today’s market, typical ducted vacuum power specifications such as watts measure the vacuum cleaner's input power. Ducted vacuum manufacturers, have been using the air watts specification in a way attempt to rate the vacuum cleaner's output rather than input power. Air watts are calculated using the following formula

(Air Flow (in CFM) x Vacuum (in inches of water lift))/8.5 = Air Watts.

Now, to you and me, that doesn’t really mean much when it comes to cleaning our homes efficiently

There is some question as to whether this is a useful specification or just a new rating to further confuse end users and make comparisons difficult. Especially when some manufacturers manage to list their machines with such high air watts.

When you do the calculations, an air watt comes to 0.9983 watt or just about the same as an ordinary watt.

It is important not to confuse air watts with airflow or sealed vacuum, which is the most important specification of all.

At Imperial Vacuum Systems we believe that Air Watts is not the best way to measure the cleaning effectiveness of a Ducted Vacuum System.

Water Lift (Sealed Vacuum)

The sealed suction of a ducted vacuum cleaner is measured in Australia as Millimetres of water lift. This rating is taken when the motor is totally sealed, and the term refers to how many millimetres the motor will vertically lift a 50mm column of water.

Water lift is what gives a vacuum cleaner the power to pick up or "lift" dirt and debris from the floor surface, while airflow then removes it to the dust bag. Ducted vacuum cleaners with more millimetres of water lift will have an easier time picking up sand, dust and other heavier soils from carpet and flooring.

Water lift is also a measure of a ducted vacuum cleaner's ability to deal with resistance within the ducted vacuum pipes and filters. This is especially important in HEPA or high filtration ducted vacuum cleaners that have more resistance due to the additional filters that the air has to pass through - You’ll notice that our range of bagless ducted vacuum models have higher water lift / sealed vacuum.

A high water lift rating also indicates that a ducted vacuum cleaner will keep performing at high levels as the filter bag, filter or receptacle fills and the filters become more and more resistant to air passing through.

The water lift of a ducted vacuum cleaner is another useful indicator of performance in that it is a means of comparing the suction of one motor to another and, generally speaking, the more water lift the more dirt that will be removed from your carpets.


Ducted vacuum airflow is by far the most important specification in terms of determining the cleaning ability of a ducted vacuum cleaner. Measured in Australia by litres per second, it is the force of this airflow across a surface that picks up the dirt and moves it to the filter bag or dirt receptacle. It is for this reason, that the more airflow, the better the cleaning ability of the vacuum cleaner.

Airflow is an excellent specification because it takes into account both the power of the ducted vacuum motor, which creates suction, as well as the resistance of the bag and filter system that this air must pass through.


Imperial Ducted Vacuum Systems have a ducted vacuum system to suit your needs and budget. Our extensive dealer network can also help you with installation of a new Imperial ducted vacuum system, upgrade of an existing ducted vacuum system or even repair your ducted vacuum system. Contact us today for more information