1. What Is System Effect?

System effect, by the book, is “the loss in performance of a fan due to adverse conditions at the fan inlet or outlet.” In plain English: it’s what happens when real-world installations don’t play by the rules of the lab. Shook’s early days in the field taught him that system effect was the catch-all for “when nothing makes sense” – but, as he learned, it’s not an excuse. It’s the trailhead for real investigation.

2. The Tell-Tale Sign: Low Air + Low Static

Let’s talk basics: In a healthy system, fan behavior follows a predictable pattern. Add resistance – like closing a damper – and the airflow drops while static pressure rises. Open things up, and airflow increases as static pressure falls. Brake horsepower (BHP) follows the curve the manufacturer gave you. It’s all neat, logical, and makes sense on paper.

System effect is what happens when the rules break down.

Shook puts it bluntly: “If you see both airflow and static pressure dropping at the same time, that’s not normal. Fan laws say that can’t happen. But when system effect is at play, both numbers are low, and suddenly the fan is working on a different, degraded curve. It’s no longer performing as rated – it’s been knocked off its game.”

That’s your giant, flashing warning sign: when the fundamentals don’t add up, start looking for system effect.

According to fan laws, you shouldn’t see both low airflow and low static pressure at the same time. If you do, it’s a giant red flag. “That’s when you know you’re dealing with something at the inlet or outlet – it’s almost always a sign of system effect,” Shook explained.

3. Ruling Out the Obvious

Before blaming system effect, Shook always checks the basics:

• Is the fan turning backwards?
• Is the belt slipping?
• Are the dampers closed or stuck?
• Is there duct leakage, missing endcaps, or open access doors?

“You’d be amazed how many times it’s something simple,” he said. “You have to rule out the obvious before you reach for system effect.”

4. Inspecting Inlet & Outlet Connections

Once the basics are clear, Shook’s process gets granular. Are turning vanes installed – and installed right? Are motorized dampers disrupting airflow? Is the canvas connection leaking, or is the fan inlet bell dented? Even something as simple as sheet metal tabs in the wrong place can throw off performance.

5. Going Deeper: Curves, Noise, RPM

If the hardware checks out, Shook digs into the specs:

• Is the fan selected on the right side of its curve?
• Is it noisy (a clue to wheel or bearing issues)?
• Is it running above max RPM?
• Is the wheel installed backwards or off-center?

These details separate the seasoned tech from the rookie.

6. Outlet Duct Configuration & Fan Rotation

One of the most frequent – and frustrating – system effect culprits Shook sees is poor duct configuration, especially at the outlet. “We call it ‘counter-flow’ in the office – when the outlet duct is installed directly opposite to the fan’s rotation. It’s like asking the airflow to do a U-turn the second it leaves the wheel,” Shook said. That kind of setup is asking for turbulence, noise, and chronic underperformance.

Shook’s seen these mistakes everywhere: elbows jammed tight against the fan outlet, undersized roof curbs, backdraft dampers that never open fully, and especially those infamous “bullhead tees” in retail spaces where air is supposed to split left and right without any turning vanes. “You’d be surprised how much energy gets wasted just because someone skipped installing a set of turning vanes,” he explains. “Without them, the air just slams into the tee and boils around, never making the turn efficiently. It’s a silent killer for performance.”

He’s also quick to remind us: a noisy fan isn’t just annoying – it’s a red flag. “If a fan is making more noise than usual, don’t ignore it. That’s often your first real clue that the system is fighting against itself.”

7. Industry Resources & Field Journals

Industry standards like AMCA diagrams and AABC guidelines are essential, but Shook swears by something more personal: the field journal. “We keep a running list of every weird thing we find – odd duct runs, mystery leaks, plastic sucked into a fan, even damage to the fan bell curve that looked like hail dents. Over the years, those notes build up a mental library you can draw on when you hit a wall.”

He encourages every tech to do the same. “It’s not just about solving today’s problem. If you make a habit of jotting down what went wrong and how you fixed it, you’ll have a troubleshooting playbook that’s worth its weight in gold. Share it. Add to it. It makes the whole team smarter, faster.”

And for those looking to deepen their knowledge, Shook recommends staying plugged into industry groups, reading the latest AMCA updates, and attending webinars like his upcoming AABC session.

8. Best Practices & Prevention

So how do the best in the business avoid running into system effect in the first place? Cody’s advice is equal parts practical and philosophical:

• Inspect everything. Don’t trust the drawings. Get eyes – and if you have to, a flashlight – on every connection, damper, and duct section, even if it means crawling into a ceiling at midnight.
• Measure, then measure again. Always compare your field readings – airflow, static, amps, and RPM – to the manufacturer’s data. If something’s off, don’t fudge the numbers or hope for the best. Find out why.
• Never overlook the basics. Check rotation, belts, damper positions, and look for leaks before diving into curve analysis.
• Document the process. Keep photos, readings, and notes. When you finally solve a mystery, write it down. You’ll thank yourself later – and so will the next tech.
• Push for continuous learning. Cody’s team regularly reviews past jobs and mistakes to spot patterns. “We don’t just want to fix problems – we want to prevent them from happening again,” he says.

Above all, Cody warns against the temptation to brute-force a solution by upsizing motors or overspeeding fans. “That’s not troubleshooting – that’s just hiding the real issue and burning more energy.”

9. Consequences & PFE Troubleshooting Tools

When system effect goes unchecked, the consequences stack up fast: wasted energy, higher utility bills, premature equipment wear, and, in the worst cases, critical spaces (like hospital rooms) that simply don’t work as designed for years. Cody recalls a decontamination room at a hospital that underperformed for more than a decade – until a third set of eyes spotted a mismatched pipe size that everyone else had missed.

To help field techs avoid these headaches, Cody’s company, Precision Flow Engineering, has developed a set of troubleshooting flowcharts and checklists. “It’s our way of making sure no one has to reinvent the wheel every time a fan acts up,” Cody explains. “You work through the list – rule out the obvious, dig into the specifics, and when you hit something weird, that’s the time to get creative and maybe bring in another set of eyes.”

He’s passionate about sharing these tools and hopes other firms will do the same. “The more we share what goes wrong – and how we fix it – the stronger the whole industry gets.”