If you’ve ever stood on the manufacturing floor next to a brushless blower that suddenly kicks on, or dug into the specs of a new HVAC system, you’ve probably come across the term “starting torque” and wondered what it actually means—especially since this small, critical detail can make or break whether your blower works as intended for your application. As a supplier who’s spent the last 12 years troubleshooting blower performance for factories, HVAC contractors, and electronics cooling specialists, I’m here to break down what starting torque for a brushless blower is, why it matters, and how to get the right number for your needs. Brushless Blower
First, let’s ground this in the basics. Brushless blowers are different from their brushed counterparts in one key way: they use an electronic commutation system instead of carbon brushes to switch current between the motor’s windings. That design eliminates the wear and tear that plagues brushed blowers, but it also changes how torque behaves when the blower first starts up—because torque is the rotational force that gets the blower wheel spinning from a dead stop, not just running steadily once it’s up to speed. So starting torque, also called breakaway torque, is exactly that: the minimum amount of rotational force the blower’s motor has to produce to overcome the static friction of the bearings, the inertia of the blower wheel, and any backpressure from the ducting or system it’s connected to, right when it turns on.
A lot of new customers I work with confuse starting torque with rated torque, and that’s where problems start. Rated torque is the steady, continuous torque the blower produces while running at its rated speed, which is what you’ll see listed on most spec sheets. But starting torque is a peak, short-lived force—usually only lasting a fraction of a second—that’s higher than rated torque. Think of it like pushing a heavy shopping cart: it takes way more effort to get it moving from a standstill than it does to keep it rolling at a steady pace. For blowers, if your starting torque is too low, the blower wheel will sit still or spin partially before getting up to speed, which leads to unnecessary wear, higher energy use, or even complete failure. If it’s too high, you’re wasting energy on force you don’t need, and you might put unnecessary stress on the blower’s components over time.
Now, why does starting torque matter so much for brushless blowers specifically? Unlike brushed blowers, which have fixed commutation that can produce spikes in torque as the brushes wear, brushless blowers have controlled, electronic commutation that lets us tailor torque more precisely—but that also means getting the starting torque wrong is a choice, not just a byproduct of a bad design. For example, if you’re installing a blower in a high-backpressure HVAC system, the ductwork creates a backpressure that pushes against the blower wheel when it starts, so you need extra starting torque to overcome that pressure and get the wheel moving. I once had a customer in the midwest who installed a standard brushless blower in a rooftop HVAC unit, not accounting for the high static pressure from the long duct run to the second floor of their office building. The blower would start, struggle for three seconds, then shut down on its overcurrent protection. It took us swapping it for a model with a 25% higher starting torque to fix the issue.
Another example is electronics cooling. Blowers in server racks or medical devices often start and stop frequently, cycling on and off every few minutes to regulate temperature. If the blower has low starting torque, it won’t get up to speed fast enough, which can lead to hot spots in server hardware or medical devices overheating during start cycles. We’ve also seen starting torque issues in automotive blowers, where space is tight and the blower wheel has to move air through small, tight hoses that add extra static resistance.
So what factors determine a brushless blower’s starting torque? Let’s get into the technical bits, but keep it practical. First, the motor design itself: the number of windings, the strength of the permanent magnets in the rotor, and the quality of the commutation electronics all play a role. Higher quality neodymium magnets, for example, produce more magnetic force, which translates to higher starting torque for the same motor size. Then there’s the blower wheel’s size and weight: a larger, heavier wheel has more inertia, so it needs more starting torque to get moving. Static pressure from the system is another big one—every blower is rated for a maximum static pressure, and the higher that pressure, the more starting torque you need, because the air pushing back on the wheel is acting against its rotational force. Bearings also matter: ball bearings have more static friction at rest than sleeve bearings, so a blower with ball bearings needs slightly higher starting torque to overcome that initial friction when starting up.
One common misconception I hear from customers is that starting torque is a fixed number. In reality, while each blower is engineered for a nominal starting torque, it can be adjusted slightly with the right controller. As a supplier, we work with customers to tune the commutation parameters of our brushless blowers’ electronic controllers to match their specific application. For example, a customer who needs a blower to start very quietly (like in a home HVAC system) might want a lower starting torque that still meets their system requirements, so we can dial back the initial current to avoid a sudden, loud start. Another customer who needs constant, reliable start cycles for a 24/7 industrial application might opt for a slightly higher starting torque to account for normal wear on bearings over time, ensuring the blower will start reliably even after 50,000 hours of operation.
I should also mention that starting torque for brushless blowers is measured in inch-pounds or newton-meters, just like any other rotational force, but the way it’s tested is specific to brushless designs. We test starting torque by applying a controlled load (mimicking static pressure from a real system) and measuring the force required to get the blower wheel to accelerate from 0 to its rated speed in a specific time frame—usually less than 100 milliseconds for most commercial and industrial blowers. That quick acceleration is key, because a slow start means the blower is using high current for longer, which wastes energy and can overheat the motor if it’s not designed for it.
Now, how do you pick the right starting torque for your application? The first step is to calculate the static pressure of your system: measure the length and diameter of your ducting, any elbows or filters, and the number of turns, then use a static pressure calculator or consult with a blower supplier to get an accurate number. Next, note the size and weight of the blower wheel you’re working with, and how often the blower will start and stop. If it’s a high-cycle application (like server cooling, cycling every 2 minutes), you’ll want a slightly higher starting torque to account for bearing wear over time, so the blower won’t struggle after thousands of start cycles. If it’s a low-cycle application (like a warehouse ventilation system, starting once a day), you can work with a lower starting torque to save on energy costs.
Another thing to watch for is datasheet dishonesty. A lot of blowers will advertise a high starting torque number on their spec sheet, but that number is often measured under ideal conditions—no static pressure, no extra load, using brand new bearings. When you add real-world load, that number drops, and you’re left with a blower that can’t start when you need it. As a supplier, we test all our blowers’ starting torque under actual operating conditions, with the specified static pressure, so our customers know exactly what they’re getting. We include that real-world starting torque number on our spec sheets, not the ideal one, because we’ve learned that honesty is the only way to build long-term trust.
Let’s circle back to that HVAC customer I mentioned earlier, because it’s a perfect example. That customer came to us after two different blowers failed, both with starting torque specs that looked good on paper. They had a 50-foot duct run to the second floor, which created 0.8 inches of static pressure at peak flow. The first blower they tried had a starting torque of 1.2 Nm, which worked at 0.2 inches of static pressure, but dropped to 0.7 Nm at 0.8 inches—too low to overcome the backpressure. The second blower had a rated starting torque of 1.5 Nm, but it was measured at 0 static pressure, so it only produced 0.9 Nm at 0.8 inches. We sent them a blower with a starting torque of 1.8 Nm, measured at their exact static pressure, and it’s been running flawlessly for three years now. That’s the kind of detail that makes a difference—understanding that starting torque isn’t just a number, it’s a performance metric tailored to your system.
If you’re currently researching brushless blowers for your project, don’t stop at the rated speed or airflow numbers. Ask about starting torque, and make sure the supplier is willing to share how that number is measured, and what the actual starting torque will be under your specific operating conditions. Too many projects get held up by a blower that won’t start, and it’s almost always because someone overlooked starting torque in the spec phase.
At the end of the day, starting torque is one of those small, technical details that has a huge impact on blower performance, energy use, and longevity. Brushless blowers’ electronic commutation makes it possible to tailor starting torque to your exact needs, as long as you work with a supplier who knows how to leverage that technology.
If you’re working on an HVAC system, industrial ventilation, electronics cooling, or any other application that relies on reliable blower performance, we’d love to help you specify the right brushless blower with the perfect starting torque for your needs. Reach out to us to discuss your project requirements, and we can walk you through the testing, tuning, and selection process to make sure your blower works as intended from the first start, and for years to come.
High-pressure Blower References
- Bose, B. K. (2006). Brushless Permanent-Magnet Motor Drives. CRC Press.
- HVAC Applications: Blower Performance and Static Pressure. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), 2020.
- Motor Starting Torque: Principles and Applications. Industrial Motor Control Magazine, Vol. 45, No. 2, 2021.
- Blower Technology for Thermal Management. Electronics Cooling Journal, Vol. 27, No. 3, 2022.
- Bearing Friction in Electric Motors and Blowers. Tribology International, Vol. 152, 2021.
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