What I've Learned About Custom Replacement Coils (And Why "Standard" HVAC Coils Rarely Are)
- Matt Calleja
- Jan 21
- 6 min read
Updated: a few seconds ago
Category: Experiences / Industry
Real-world coils we've measured and assessed. Some show damage, others are discontinued - all needed custom solutions.
From Commercial Construction to Custom HVAC Coil Manufacturing: My Journey
I spent years as a project manager in commercial construction, coordinating the trades that make buildings work - electrical, plumbing, fire protection, and mechanical systems.
The mechanical side pulled me in. There's something about HVAC that most people don't see or think about until it stops working. It's the hidden infrastructure that keeps server rooms cool, production floors comfortable, and hospitals at precise temperatures. In 2017, I got deep into the mechanical and HVAC world, learning the technical side - load calculations, ductwork design, refrigeration cycles, system balancing. By 2022, I'd moved into coil sales specifically, working with contractors and facility managers who needed replacement parts for aging commercial systems.
What drew me away from the corporate climb? The chance to build something. Not navigate politics or chase the next rung on the ladder - but to directly help others achieve project success with reliable HVAC solutions.
What I didn't realize was how much this work would change the way I think about problem-solving.
The Hidden Importance of HVAC Coils in Commercial Operations
Why Coil Failures Create Business Crises
The biggest surprise when I started? The magnitude at which coils are part of business operations and their impact on daily operations.
When an evaporator coil or condenser coil fails:
Production lines stop
Server rooms overheat
Entire buildings become uncomfortable
Operations scramble for expensive emergency HVAC repairs
A failed coil isn't just an inconvenience - it's a crisis that demands immediate attention and can cost thousands in lost productivity.
Common Myths About HVAC Coils That Cost Money
Here are the misconceptions about replacement coils I hear constantly:
MYTH: "A coil is a coil - they're all basically the same."
Reality: Design, materials, circuiting, and fin spacing dramatically affect performance and longevity. Not all replacement coils are created equal.
MYTH: "If the unit still cools, the coil is fine."
Reality: A struggling coil costs you in energy bills long before it completely fails. Inefficient coils can increase HVAC operating costs by 20-30%.
MYTH: "Leaks always mean bad manufacturing."
Reality: Most coil leaks come from corrosion (environment, cleaners, installation), vibration, or airflow issues - not factory defects.
MYTH: "Just match the size and tonnage."
Reality: Real-world HVAC systems operate outside ideal design conditions. Dimensions, airflow patterns, and cabinet constraints matter just as much as tonnage ratings.
MYTH: "Just copy the OEM coil."
Reality: OEM parts get discontinued. Buildings age. Equipment gets modified. What worked in 2005 might not even be available in 2026. OEM coil replacements aren't always an option.
MYTH: "Coils fail randomly."
Reality: They fail for specific, identifiable reasons - and custom coil design can address those root causes.
What the HVAC Coil Industry Really Looks Like
"Standard" HVAC Systems Rarely Stay Standard
On paper, HVAC systems are built around "standard" sizes, tonnages, and components.
In reality:
Buildings age and cooling needs change
Equipment gets modified over time
OEM replacement parts get discontinued
Systems operate outside ideal design conditions
Surrounding infrastructure doesn't always match the original specs
The result? Real-world HVAC systems almost never match the catalog assumptions they were designed under.
How the HVAC Industry Has Changed
Technology:
Higher-efficiency systems mean coils do more work in tighter spaces
New refrigerants require material and design changes
Thinner metals and tighter tolerances improve efficiency but reduce forgiveness
Controls and diagnostics improved, but physical heat transfer is still the bottleneck
Bottom line: Tech evolved fast, but replacement coils now fail faster when systems aren't perfectly balanced.
Customer Expectations for HVAC Repairs:
Customers are less tolerant of:
Long downtime waiting for OEM replacement coils
"Close enough" replacements that don't fit properly
Repeat coil failures requiring multiple service calls
They care more about:
Fit-first solutions that work the first time
Predictable performance and longevity
Avoiding redesigns of surrounding equipment
Speed and accuracy now matter more than lowest upfront cost for commercial HVAC replacements.
Regulations:
DOE efficiency standards keep rising
EPA refrigerant regulations keep changing
OEMs discontinue coil models faster than ever
This pushes more HVAC systems into a gray area where OEM support disappears, but the equipment is still very much in service.
Why HVAC Coils Fail and When Custom Replacement Makes Sense
Common Causes of Coil Failure
Problems I see repeatedly in failed HVAC coils:
Coils failing before their expected 10-15 year lifespan
OEM replacement coils that don't fit without modification
Airflow or pressure issues caused by incorrect "drop-in" parts
Corrosion tied to environment, cleaners, or installation - not age
Vibration damage from poor cabinet fit
Why Businesses Choose Custom Replacement Coils
Not because they want something fancy - but because:
The original OEM coil no longer exists or is on permanent backorder
The cabinet opening doesn't match modern coil designs
The system has known issues they want corrected (airflow, efficiency)
Replacing the entire HVAC unit would cost 5-10x more
They need specific dimensions for tight retrofit applications
Custom replacement becomes the practical option, not the premium one.
Custom vs OEM Replacement Coils: What You Need to Know
The Biggest Misconception About Custom HVAC Coils
"Custom = more expensive, slower, and only for extreme cases."
The truth about custom replacement coils:
Custom is often cheaper than repeated OEM failures
Lead times are competitive (often 2-4 weeks) when the alternative is redesign or rework
Most custom jobs are about fit and correction, not complexity
Custom isn't about doing something exotic - it's about doing the right thing once.
When Custom Replacement Coils Make Sense
Custom HVAC coils are worth it when:
OEM coils are discontinued or unavailable
Exact dimensions matter for retrofit applications
Space constraints can't change
The original design had known performance issues
Downtime or repeat service calls are costly
The HVAC system is otherwise sound and worth preserving
If the system stays, the coil should fit it - not the other way around.
When Off-the-Shelf OEM Coils Work
OEM replacement coils make sense when:
The HVAC system is new and standard
OEM parts are readily available with short lead times
There's no history of repeat failure
Small performance compromises are acceptable
Budget is extremely tight
Not every job needs custom - and knowing that builds trust with customers.
The "Repeat Failure" Job
The situation:
A commercial customer was on their third replacement coil in the same rooftop unit over just a few years. Each time, they bought the OEM part. Each time, it failed within 18 months.
The temptation:
Just build another replacement and move on. Collect the payment and let them deal with it.
What we did differently:
We stopped and asked:
Why is this HVAC coil failing repeatedly?
What hasn't changed in the system?
What keeps failing around the coil?
What we discovered:
Chronic airflow imbalance causing hot spots
Vibration causing tube rub-through and refrigerant leaks
A coil design that never fit the cabinet properly, creating stress points
The change:
We designed a custom replacement coil that:
Adjusted refrigerant circuiting for better heat distribution
Modified mounting supports to eliminate vibration
Matched fin density to actual airflow conditions
Addressed stress points at cabinet interface
The outcome:
That custom coil outlasted the previous three OEM replacements combined. It's still running strong three years later.
What it changed forever:
We stopped seeing custom as "replacement" and started seeing it as correction. Every coil failure is a chance to solve the underlying problem.
The Real Value of Experience in HVAC Coil Design
After years in commercial construction project management and now deep in the custom coil business, here's what I know:
The technical knowledge matters. Understanding materials, refrigerant circuiting, heat transfer, and airflow is essential for quality HVAC coil manufacturing.
But the real skill is asking the right questions:
Why did the last coil fail?
What's different about this installation?
What hasn't been addressed in previous repairs?
What's the actual problem we're solving?
Because in the HVAC industry, "standard" rarely is.
And custom coils aren't about being fancy - they're about being right.
The Future of Custom HVAC Coil Replacement
The HVAC industry keeps evolving. Regulations change. Technology advances. Customer expectations rise. Refrigerants transition to lower-GWP alternatives.
But one thing stays constant: systems need to work, and when they don't, someone needs to figure out why.
That's where custom replacement coils come in - not as a premium option, but as the practical solution when the OEM catalog doesn't have the answer.
If you're dealing with repeat coil failures, discontinued OEM parts, or HVAC systems that never quite perform right - let's talk. Because the right replacement coil isn't always the obvious one.
Get Expert Help with Custom HVAC Coil Replacement
Dealing with a coil problem that won't stay fixed?
Let's figure out why. Contact us to discuss your HVAC system and find the right solution - whether that's custom or OEM.
Have questions about custom vs OEM replacement coils?
Drop a comment below or reach out. I'm happy to help you think through your options and determine the best approach for your specific situation.