LEAF BLOWER TIPS: CFM VS. MPH
WHAT’S REALLY IMPORTANT FOR LEAF BLOWER POWER AND PERFORMANCE
To start, let's be clear, in the world of leaf blowers you get what you pay for. You don’t want to buy the cheapest leaf blower on the market. It doesn’t matter if you’re a wise homeowner or someone in charge of purchasing professional landscaping equipment, you should choose a high-quality leaf blower.
That means you’ll be looking at a lot of data. RPM, Volts, Watts, BTU, AMP, MPH, CFM, CC, HP, GPM, PSI are some of the units of measure we regularly use when determining the ability of power equipment to perform a specific job. When used together, they can sometimes be confusing. We also often assume the higher numbers, are an indication of a better product, but this false assumption could lead to a rude awakening, especially when it comes to leaf blowers. Let's take a look at a leaf blower's units of measure, CFM and MPH, and how it affects performance and what you want to accomplish.
WHAT IS LEAF BLOWER CFM?
Years ago the term CFM, or Cubic Feet per Minute, was not as well known as it is today. Those that struggle with the term tend to be new to leaf blower purchasing or may struggle with the difference between CFM and MPH. CFM is the measure of the volumetric flow of the unit. That is the total amount of airflow that passes through the leaf blower’s nozzle per minute. This means your leaf blower will create more air if the CFM number is higher. In less time, you’ll be able to clean a larger area.
WHAT IS LEAF BLOWER MPH?
With our experience with vehicles, MPH is likely very familiar to most of us. It is the velocity of the wind being expelled by the unit. MPH stands for miles per hour and is a unit of measurement for speed. It measures the pace at which air flows through the nozzle of the leaf blower.
WHICH IS MORE IMPORTANT, CFM OR MPH?
They seem like the same thing, right? However, they are not the same. In fact, it is best to take BOTH into consideration when determining the ability of your leaf blower to do its job. One way to think about it is, that a leaf blower’s engine generates force. The force produces a constant volumetric flow or CFM’s regardless of the surface it impacts. On the other hand, when it comes to the MPH, the velocity is affected by both the force and the pipe diameter.
Here is another example if you’re still unsure about the distinction between the two.
Think of it in terms of a water pressure washer. They are measured using PSI (Pound-force per Square Inch) and GPM (Gallons Per Minute). The pump on the pressure washer puts out the water at a set rate of gallons per minute, this would be your CFMs. Though there would be fluctuation, this is what the pump is set up to push out at a consistent rate.
What determines the pound-force per square inch, or MPH for our comparison, is the unloader valve, hose, and tip being used. Adjusting the unloader valve, using a larger hose, or a tip with a smaller exit hole will dramatically change the speed at which the water leaves the pressure washer gun, without changing the GPMs at all. Having larger GPMs allows you to have the unloader valve, hose, and tip opening larger and still get good pressure. It is reasonable to also assume that if you were to change the GPMs, removing that constant force, would change the amount of water pouring into the unloader valve, hose, and out the tip. This would mean you would have to close the unloader valve more, have a smaller hose and a smaller tip to achieve the same PSI going out, but it would also mean a smaller area would be covered. This example shows how both variables become an important part of determining the performance of the whole unit.
As a result, we may deduce that CFM can be used to determine the engine’s power and the pace at which it can blow air. While at the same time using MPH to figure out how fast items can be blown, or calculate the effective distance that we can blow. So keeping our example in mind, let's take a look at a couple of combinations of CFMs and MPH and how it relates to performance.
WHAT IS A GOOD CFM / MPH FOR A LEAF BLOWER?
Many customers wonder what a suitable range for leaf blower CFM/MPH? On a consumer level, CFMs: 450-500 / MPH: 150-190 is recommended. Which would be blowing on about half an acre or less. If you are a commercial company, have property exceeding a half-acre, or require multiple fall cleanups, CFMs: 900-1000+ / MPH: 200-239+ is recommended. So which, CFM or MPH, is more essential? Well... that depends. Before we take a look at a side by side comparison below, take a look at the graphic to see what you can expect out of the unit type you may have already been looking at.
LOW CFM / HIGH MPH
If you go to your local store and find a great deal on a leaf blower that has a rather low CFM to MPH ratio, it is likely the manufacturer increased the MPH by reducing the exit tube diameter. As a result, the blower may move leaves, but it will move a much smaller area when doing so. If you have a large area to cover, this kind of blower would take forever to cover your whole yard.
HIGH CFM / LOW MPH
A leaf blower with a high CFM but a low MPH rating likely would have a much larger exit tube mouth. This blower would actually be more useful than the previously mentioned blower, but still rather limited. This blower would be suitable for blowing dry leaves, hay, and maybe even tiny rocks. The problems would become more apparent when the items to be blown get heavy due to being larger in size or damp from rain and sticking together.
HIGH CFM / HIGH MPH
If you got this far, then you are thinking a good balance of the two, both measurements being high, is the best combination. With that said, you can expect to pay a lot more to get this balance.
What you should have also gathered, is the diameter of the exit pipe is almost as important as these two measuring units. Because the pipe's physical presence impairs airflow, it affects the unit’s CFMs. The tube causes friction that slows the air. As a result, some manufacturers manipulate their CFM numbers by calculating them without using the tube attachment. This means that, similar to cars and mpg, what numbers they claim on the box, may not reflect real-life situations.
In the end, as explained in our example, the CFM number should always be as high as possible. The MPH is a parameter that can vary even as you use the unit. So even though a good MPH is necessary for leaf blowing success, if your budget won’t allow a more expensive unit, MPH may be sacrificed to some degree depending on what you are regularly attempting to blow.
WHAT IS BLOWING FORCE?
Blowing Force is being included on more leaf blower packaging now and is measured in Newtons. A Newton is a force unit that combines air velocity and volume into a single, easy-to-understand measurement. Other more common blower parameters, such as air velocity [mph] and air volume [cfm], are figured in along with tube diameter, air pressure, temperature, and humidity to determine its value. Blowers produced between 8 N (Newtons) and 41+ N depending on the size and type of blower. Since you can move more material with a higher newton, it becomes easier using this single number method. Bigger means better.
In the end, ensuring your blower is operating at peak performance will affect what it can and cannot blow. Shop The ROP Shop for replacement parts once you have made your decision on what blower to buy. Whether you use Blowing Force or stick with CFM and MPH they are all significant figures to consider when evaluating the strength of a leaf blower’s airflow. When you take them all into account, you’ll be able to get the most air for the money.
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