Let’s talk airflow. We live back in the woods on a half-acre with fifteen 100-foot tall oak trees. For years I’ve imagined sharing leaf blowing airflow lessons with my fellow airheads. Let’s take a look at the mad airflow skills you can master while blowing leaves.
“If you don’t measure, you’re just guessing.” So before you get to work, you’ve gotta know the numbers. Here is the leaf-blowing scenario at our home.
How many leaves? According to an estimate by J.W. Teaford (a noted professional wetland scientist), the average 100-foot oak tree sheds about two million leaves each year. We have 15, 100-foot oak trees in my yard. So if you multiply two million leaves times 15 trees, we get an annual leaf pickup of 30 million leaves at our home.
The leaf blower – My weapon of choice: the Stihl Magnum® Model BR 600. This baby moves 677 cubic feet of air per minute. It has a 238 mile-per-hour maximum discharge velocity and it’s built in the USA. It can blow leaves up to 40 feet away. Yes, ear protection is a must. Hint: buy the best leaf blower you can afford. The added cubic feet per minute capability is worth the money and it will pay you back with joy and happiness for years to come. Clean the leaves sticking to the intake often, to maintain maximum airflow.
Air density – On a mild fall day the air measures 70 degrees and weighs 0.075 pounds per cubic foot. So the math is as follows: Multiply my Magnum’s 677 cubic feet of air per minute times 0.075 pounds and you get 51 pounds of leaf moving force per minute. Per hour, that’s 3060 pounds of airflow at your command to clean the yard. Beats the heck out of a rake, doesn’t it? As the temperature outside drops, the weight of air increases. On a cold day, you’ll get an extra 300 pounds of work per hour. Blow leaves when it’s cold!
Leaf weight – A single oak leaf averages 0.18 ounce. At two million leaves per year, that’s 22,500 pounds of leaves. Multiply that by 15 trees and that equals 337,500 pounds of leaves annually. Guess what? A wet leaf is double the weight of a dry leaf! Wet leaves may increase my leaf load to 675,000 pounds. So, blow leaves when it’s dry. This is a good excuse to blow leaves in the afternoon when the sun has dried up the dew.
Leaf Blowing Airflow Principles
Your leaf blower offers a unique opportunity to see air in action. If you pay attention, you can observe many essential air patterns and see the airflow principles of an HVAC system repeated over and over. If you’re a real airhead, you will soon harness the powers of airflow until the leaves beg for mercy.
Become a Nozzle Whizz
The discharge nozzle of a leaf blower is designed to increase air velocity as the air leaves the tube. The rule of thumb is the higher the velocity; typically the greater the power to move leaves.
Once the air leaves the nozzle, the air stream fans out and the velocity of the air begins to decrease. This principle also applies to every supply register. The farther from the nozzle the slower the air movement, the less leaves
move. Your job is to find the sweet spot of the air stream matching your method of attack on the leaves.On the other hand, if the nozzle is too close to the leaves, the air weight pulls in additional air around the air stream and leaves fly all over the place. You’ll do better by backing away from the leaves and finding that sweet spot. By study and practice as you gain experience, you can double the work you accomplish.
The Cone Shaped Path Technique
Once you master the nozzle and your leaf moving skills increase, you’ll find a cone-shaped path in the leaves at your feet. You’ll naturally learn to move the nozzle back and forth neatly driving a wave of leaves in an increasing wider path before you. This path will be from 6 to 15-feet wide depending on the strength of your blower.
The optimum depth of the cone-shaped path depends on the volume of leaves you are pushing. With a light leaf
load, you may make it all the way to the location of the pick-up pile. With deep leaves you’ll want to back up every 10 feet and move to the left or right and being another coned shaped path. You will consistently move the sea of leaves closer to their final destination.
Blowing Against the Wall
As you move across the yard, driving the leaves with your airflow, soon you’ll run smack into the “wall of leaves.” As the leaves pile up and get deeper the weight of all those leaves becomes heavier. Soon the wall of leaves begins to restrict your airflow and progress slows. This can be compared to a restricted air filter.
One solution is to blow a thinner layer of leaves off the top of the leaf wall onto the ground behind the wall. In extreme cases you can blow the leaves from the thin layer you removed all the way to the pick-up pile. Then go back and send the next layer to leaf never-never land.
When leaves get really deep, use your leaf blower as an air knife and slice a loaf of leaves off the back of the pile and drive them to the leaf graveyard.
The Wind is Airflow Too
When the wind is blowing, if Mother Nature smiles upon you, the prevailing wind is gusting in the same direction you are driving your leaves. Unfortunately, the odds are against you since there are four points on the compass and 3 of them don’t match your direction.
When the wind blows, especially if it persists, odds are your best bet is to go find something else to do until it subsides or wait until another day. On the other hand, if it’s really windy and you enjoy the fall colors, love a clean lawn, and crave the smell of the leaves, keep on leaf blowing.
Final Leaf Blowing Advice
As much as I love to blow leaves, there are some pitfalls to be aware of as you engage in this most delightful practice. I have learned from sad experience that each of the following is true.
Use caution when using a leaf blower near beehive … use your imagination.
- When burning a few leaves to fill the yard with the best smell of fall, use basic fire safety. This will prevent your neighbors from calling the fire department because the 100-foot pile of leaves on the street in front of your home is burning out of control.
- Should you have the unfortunate loss of freedom because your town has outlawed leaf blowers … just pay the fine. To me, leaf blowing is worth it.
Rob “Doc” Falke serves the industry as president of National Comfort Institute — an HVAC-based training company and membership organization. You can contact Doc at firstname.lastname@example.org or call him at 800-633-7058. Go to NCI’s website at nationalcomfortinstitute.com for free information, articles, and downloads.