Blower MPH Vs CFM: Which One is More Important?
We’ve been talking a lot about blowers with both a cordless blower shootout and backpack blower shootout under our belts in the last couple of months. And in a discussion about why the manufacturer’s claimed specs are pretty far off from reality, it also opens up other questions. One of the most common we come across is the blower MPH vs CFM debate. Which one is actually more important?
Well, both… and neither.
Let’s take a look at each and throw another term into the mix to help you sort this out.
MPH – Miles per Hour
In the blower MPH vs CFM conversation, the miles per hour as a measurement of airspeed is pretty easy to understand. We’re used to speeds in a car, wind speeds, and other areas where speed is measured with this measurement. It’s how many miles you will go if you travel for one hour at a constant rate.
A blower that produces 200 MPH windspeed would push a burst of air 200 miles away in an hour if that burst could maintain it’s speed. Simple enough.
CFM – Cubic Feet per Minute
Blower CFM, or cubic feet per minute, measures the volume of air leaving the blower. In this case, the impeller creates a vacuum effect, pulling air through itself and pushing it out the other end. The angle, length, and speed of rotation of the blades determine how much air moves through and determines both the speed and volume of air moving. Consider a backpack blower that claims to get 1000 CFM (and let’s assume you actually get it for the sake of the example)
Consider a backpack blower that claims to get 1000 CFM (and let’s assume you actually get it for the sake of the example). That 1000 CFMs means that the blower moves enough to fill a cube that’s 10 feet high, 10 feet wide, and 10 feet long in 1 minute.
MPH VS CFM
Airspeed is important because it takes more of it to move heavier objects. Dry grass is one thing. pebbles, mulch, and wet leaves are another. Air volume is important because you need more to move debris in a larger area. But is blower MPH or CFM more important? Consider a couple of examples.
Take a straw and blow air through it at 300 MPH. You’ll make an impressive mess with your glass of milk or make a pretty effective blow dart gun, but you’ll accomplish very little in your yard. You’re in a low CFM situation, and the airspeed can only affect a small area.
On the other side of the coin, let’s say that you can produce 20,000 CFM but only get 15 MPH out of it. You get a nice breeze for a hot day. You and four of your closest friends can stay cool, but you’re only going to be moving the lightest sawdust. The low airspeed means you’re not moving much weight around.
You need a combination of both MPH and CFM to get the job done, but is there a correct balance? Or at least a way to decide how much work a blower accomplishes for a comparison to others?
Newton force is the number you want to look for when comparing blowers. Because of the way it is tested, it takes the effect of both the MPH and CFM to give you one number representing the total amount of force a blower produces. In our shootouts, we found cordless blowers producing anywhere from 8 to 17 NM (Newton meters) while the Pro backpack blowers produce between 28 and 39 NM. With a simple “bigger is better” kind of measurement, it’s much easier to see which blower is more powerful.
The Final Word
So blower MPH vs CFM – which one is more important?