CFM vs LIFT
While shopping around for a new portable extractor, truck mount, or any other vacuum system, you’ll likely be considering–among other things–how “strong” the vacuum is. Manufacturers will throw around specs like water lift, inches of mercury, and CFM when talking about vacuum power, but what the heck do they mean? Which is better to have more of? We’ll break down the basics for you below so you can pick your next machine with confidence!
What is Lift:
Measured in either inches of water or in inches of mercury, lift is a measure of vacuum motor strength, or its ability to overcome resistance. To get a little scientific–this measurement is how far the vacuum can vertically lift a 1” column of either water or mercury with a complete seal (pictured below). 1 inch of Mercury lift roughly equals 13.6 inches of water lift.
In other words, lift measures a vacuum’s power to pick up or “lift” debris from the surface; vacuums with more inches of water lift will have an easier time pulling air through carpets to pick up dirt and moisture. Without lift, you won’t pull up any water or dirt from the carpet.
So if lift measure’s a vacuum’s strength, what other measurements matter? Is the vacuum with the highest lift automatically the best? The short answer is no, and that’s why we need to talk about CFM.
What is CFM:
It stands for Cubic Feet per Minute of air. This is a measure of airflow, or how much air is being moved by your machine every minute. Again, the higher the better. The airflow is what actually carries the recovered water and dirt through your wand, tool, or hose back to the machine. Airflow is equally if not more important in the vacuum power equation as lift is–without it, anything you picked up with your vacuum would fall right back out the second you pick the wand up off the carpet! Airflow is also what helps your wand or tool to “stick”, or form a partial seal with the carpet. And remember, Lift is a measurement of sealed suction, so having high enough CFMs to seal the wand to the carpet is crucial to getting the maximum available lift at the wand!
So is maxing out CFM the best way to go then? Well…no, not exactly that either. The key to having the most effective vacuum is a balance of both lift and CFM that suits your needs. The two work in tandem to clean effectively, and too little of either will result in an ineffective vacuum motor!
What About Airwatts?
Okay, so now let’s say you want to compare two vacuum systems, one has higher lift and the other has higher CFM. Both may be better suited than the other in specific situations, but how do you determine which is the most “powerful” overall? Enter, the airwatt…
An Airwatt is a measurement of the effectiveness of vacuum motors, factoring in both airflow and lift. To calculate airwatts you can use the formula: (Inches of Water Lift x CFM) ÷ 8.5. Since this measurement depends on a combination of both lift and CFM, it can be another way to compare the output of two vacuum systems, with the higher airwatts being the most generally effective.
Let’s create a simplified example scenario with 3 hypothetical extractors. Each will have a total of 300 “points” split between lift and CFM. Let’s see what different balances look like when you calculate airwatts.
- Balanced Extractor: 150″ water lift, 150 CFM | Airwatts = 2,647
- Lift-heavy Extractor: 250″ water lift, 50 CFM | Airwatts = 1,470
- CFM-heavy Extractor: 100″water lift, 200CFM | Airwatts = 2,352
So as you can see, the balanced vacuum had the most airwatts, meaning it was the most effective of the three. This was a simplified example but the point it illustrates holds true in real-world scenarios–the most effective vacuums have an ideal balance of lift and CFM. This is why knowing both measurements is important; in the scenario above, if all three machines only advertised water lift, the second machine would appear to be a clear winner, but once we know the whole picture we see it was actually the least effective of the three!
Different vacuum motors strike different balances, some opting for more lift over CFM and others vise versa. The higher the lift, the better the motor is at overcoming resistance, the higher the CFM, the higher the volume of air the motor can move, and the longer the range it can perform effectively at. Having lift is important, and so is having lots of CFM, but more important than having a lot of either is having an effective balance of the two. This is why when considering vacuum motors, it’s crucial to know all of the stats about a vacuum to paint a complete picture. Knowing what these measurements mean and how they relate to each other will ensure you can always pick the machines best suited to the job at hand!