Loaded Filters, Unchecked Strainers, Bent Fins: The Hidden Efficiency Killers
- Alex Khachaturian
- Sep 22
- 6 min read
Promise: Why the smallest blockages in your system cause the biggest failures, and how to stop them before they choke efficiency, comfort, and trust.
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TL;DR
Loaded filters, strainers, and bent fins quietly sabotage efficiency long before alarms catch them.
Those “little” dirty filter alarms? They matter, they measure pressure differential, and ignoring them breeds mold, complaints, and energy waste.
Airflow restrictions are invisible lies that make your BAS look trustworthy when it isn’t.
Quick Links For This Article
A Few Brief Stories
Loaded Filters, When Airflow Lies
I once walked up to a condenser where the fins weren’t just bent, they were mangled beyond repair. Someone had actually carved their name into the aluminum with a screwdriver, like it was an Etch A Sketch.
That condenser couldn’t breathe. Airflow collapsed, efficiency tanked, and the system strained just to limp along. And the worst part? The damage wasn’t from age or failure, it was from ignorance. You don’t know what you don’t know.
👉 Related Article: How to Know What you Don't Know
The same lesson shows up again and again in filters. I’ve opened air handler filter bays after a low-airflow complaint, only to find black, sagging filters disintegrating inside the fan housing. Moisture from nearby coils had turned them into moldy paste blowing straight into the supply air. Nothing like a lungful of mildew to start your Monday.
And here’s the kicker: those little dirty filter alarms everyone ignores? They work. They measure the pressure drop across the filter. When it spikes, airflow is choking. Ignore it, and you’re not just burning energy, you’re pushing contaminants into the occupied space.
And if you think that’s bad, wait until you hear what happened at NASA’s Jet Propulsion Lab.
Clogged Strainers, Chilled Water Slowdown
Back when I was wrenching at JPL, our chilled water plant was keeping thousands of servers alive, servers crunching data from Mars rovers and Voyager probes. High stakes. No downtime.
Then the system started choking. Pumps cavitating, chillers pulling max amps, alarms tripping like popcorn. On the graphics? Everything looked normal.
I asked about the strainers. Blank stares. Nobody had checked. Finally, they opened one up.
What poured out wasn’t sludge, it was a brick of rust, weld slag, and pipe scale fused with biofilm. Flow was strangled at the source.
We cleaned it, flushed the loop, and instantly the plant came back to life. Temps locked in, pumps hummed smooth, chillers efficient. The servers cooled, and the mission-critical data kept flowing.
Lesson: strainers aren’t a footnote. They’re the first line of defense. Ignore them, and even billion-dollar operations can grind to a halt.
Quick Win: Prove It in 30 Seconds
Next time you’re on a complaint call:
Don’t argue with the occupant or trust the BAS graphics.
Pull out a portable manometer or thermometer.
Take a real-time reading at the filter, coil, or supply.
Show the delta to the facility manager.
Nothing cuts through doubt faster than measured proof. It’s hard to argue with a manometer in your hand, though some managers will still try.
Recommended Gear
Best for: Spot-checking airflow restrictions at filters, coils, and strainers.
What you’ll get: Compact, accurate ΔP readings in seconds.
How to use it: Clip the leads across a filter bank or coil, compare against baseline.
Field Tip: Take a photo of the live reading and email it to the facility manager. Instant proof.
Pro Tip: Build a library of “healthy” vs. “loaded” ΔP values for common equipment. Cuts diagnosis time in half.
Best for: Restoring airflow on coils with bent/damaged fins (hail, debris, “curious” hands).
What you’ll get: Multi-pitch combs that match common fin densities (FPI)
How to use it: Match comb to fin pitch; start at the undamaged edge and work inward.
Field Tip: Shine a flashlight through the coil first, if you can’t see light, neither can the air.
Pro Tip: If a section looks like “aluminum graffiti,” stop combing and price a coil, over-combing tears fins and makes it worse.
Best for: Inspecting strainers, piping, and tight coil/fan compartments without tearing the system apart.
What you’ll get: Self-contained camera with light and display (no phone needed), dual lenses for wider/side views, IP67 rating, and a semi-rigid cable.
How to use it: Snake into Y-strainers and suspect sections; record photos/video to show debris buildup before you drain/tear down.
Field Tip: Use it post-construction or after “mystery” ΔP spikes, the camera pays for itself the first time you catch weld slag before a shutdown.
Pro Tip: Build a quick clip library (clean vs. clogged) to train operators on what “normal” looks like.
The Field Playbook: Finding Hidden Efficiency Killers
Airflow issues aren’t complicated, but they are sneaky. Here’s how to catch them systematically:
1. Start at the filters.
Don’t just peek through the access door and say, “looks fine.”
If you can write your name in the dust, it’s not fine.
Take ΔP readings across every filter bank.
Pro move: log baseline ΔP at install and compare on every visit.
2. Move to the strainers.
Strainers are like the appendix, ignored until they nearly kill you.
Blow them down monthly, weekly if it’s post-construction.
If you need a shovel to clean your strainer, something’s gone wrong.
3. Inspect fins and coils.
Shine a flashlight through the coil, if you can’t see light, neither can the air.
Bent fins collapse airflow like a kinked straw.
Straighten what you can with a fin comb. If it looks like graffiti art, start pricing replacements.
4. Check the fans and belts.
Loaded filters = higher static = belt life cut in half.
A squealing fan belt is just a loaded filter complaining in another language.
Always check alignment and tension after airflow restrictions are fixed.
5. Verify the alarms.
Filter switches and flow sensors aren’t decorations.
Calibrate them and teach the customer what they mean.
A dirty filter alarm is not a suggestion.
6. Seasonal sequence.
Cooling season? Filters load faster with pollen.
Heating season? Moisture around coils turns filters into soggy cardboard.
Document seasonal differences, facility managers appreciate patterns.
7. Document, document, document.
Take readings, photos, and notes.
Nothing saves you from the blame game faster than proof.
Troubleshooting Guide
Symptom | Likely Cause | Fix |
Low airflow, but BAS shows “normal” | Loaded filters | Check ΔP, replace filters |
Pump cavitation, noisy vibration | Plugged strainer | Blow down or clean strainer |
Chiller amps climbing, poor cooling | Coil fouling or bent fins | Clean coil, comb fins, check refrigerant |
Occupant complaints: hot/cold, odors | Moldy/disintegrating filters | Replace filters, sanitize, check coil leaks |
Short cycling, nuisance alarms | Airflow restriction | Trace back to filters, strainers, fins |
Economizer won’t track properly | Coil face plugged with debris | Clean thoroughly, retest actuator |
Humidity keeps spiking | Filters bypassing/leaking | Seal filter frames, replace media |
Smoke detector nuisance trips | Dust bypass from collapsed filters | Inspect, reseal, replace filters |
Recommended Books
The Right Kind of Crazy
Written by Adam Steltzner
Best for: Understanding why small oversights in engineering create massive failures.
An Astronaut’s Guide to Life on Earth
Written by Chris Hadfield
Best for: Seeing how meticulous attention to small failures creates resilience in high-stakes environments.
Maintenance and Reliability Best Practices
Written by Ramesh Gulati
Best for: Facilities and service leaders who want a structured approach to inspections, PMs, and troubleshooting.
Field Checklist
Spot-check ΔP across every filter bank you open.
Verify filter alarms trip when expected.
Blow down strainers monthly (weekly after new construction).
Shine a flashlight through coils to check blockage.
Carry a fin comb and manometer at all times.
Log baseline ΔP after install for every system.
Compare field readings against BAS trends.
Train operators to spot the early signs.
Document airflow issues with readings + photos.
Always check belts/fans after restrictions are cleared.
Results & ROI
Catching these hidden blockages early means:
Fewer callbacks (no chasing phantom BAS alarms).
Energy savings (dirty filters can add 10–15% to fan power).
Healthier IAQ (no moldy paste in the fan housing).
Longer belt/fan life.
Trust, facility managers see you as the tech who proves, not guesses.
And if you’re still not convinced? Go carve your name into a condenser coil. Then watch how fast your efficiency disappears. (Kidding. Don’t. Please don’t.)
Wrap-Up
Airflow is invisible. That’s why it’s the easiest way for your BAS to lie, and for you to get caught chasing ghosts. Loaded filters, unchecked strainers, bent fins, they’re not glamorous problems, but they’re the ones that quietly choke efficiency, comfort, and credibility.
Catch them early, prove them with real measurements, and you’ll never be the tech who gets fooled by “normal” graphics again.
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