Airflow Reality Check:
Can Your Ductwork Actually Handle 3 Tons + a 3.5-Ton Coil?
(Mike’s CFM Rules You Wish Installers Would Follow)
Let’s get something out of the way before we even talk about CFM numbers:
Your Goodman 3-Ton R-32 system is only as strong as the ductwork feeding it.
I don’t care how shiny the condenser is.
I don’t care how efficient the coil is.
I don’t care how the brochure describes the SEER2 rating.
If your ducts choke airflow, your 3-ton system becomes a 2-ton system the moment you turn it on.
And if your ducts REALLY choke airflow, your 3-ton system becomes a no-ton system that freezes, sweats, roars, and dies way too young.
This is why Goodman pairs that 3-ton R-32 condenser with a 3.5-ton CHPTA4230C3 coil — bigger coil = lower static = easier airflow.
But even the best evaporator coil in the world is useless if the duct system can’t actually deliver or return the air it needs.
This is a Mike-level truth session.
1. First Rule: A 3-Ton System Needs REAL CFM — Not “Hope and Prayer” Airflow
A 3-ton Goodman system MUST move:
1,200 – 1,500 CFM
(400–500 CFM per ton)
Anyone telling you otherwise is working from duct charts written for mobile homes in 1978.
1,200–1,500 CFM isn’t “ideal.”
It’s REQUIRED.
At 1,200 CFM, your system is functional.
At 1,500 CFM, your system is optimal — especially with a bigger coil.
This range is backed by lab-tested rules similar to those found in the [Air Handler Operational CFM Output Verification Document], which shows the blower’s sweet spot for cooling requires that exact airflow rate.
Fall below this number and:
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coil stays too cold
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system freezes
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humidity skyrockets
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rooms feel uneven
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blower screams
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compressor overheats
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system loses 20–50% capacity
Airflow is oxygen.
Without it, the system suffocates.
2. Rule #2: Return Ducts Are the REAL Limiter — Not Supplies
Most homeowners obsess about supply vents.
But the supply is rarely the real bottleneck.
The return is the part nobody sizes correctly.
Most returns I see are:
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too narrow
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too long
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too restrictive
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using a 1" filter rack from the 1980s
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choked by a grille with tiny louvers
The [Residential Return-Air Velocity & Noise Threshold Chart] makes it painfully clear:
Return air velocity MUST stay under 350–400 FPM
(Feet Per Minute)
If velocity goes above that:
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noise increases drastically
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turbulence spikes
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blower RPM increases
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static pressure skyrockets
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efficiency drops
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temperature splits collapse
A 10" or 12" return duct feeding a 3-ton blower is like sucking a milkshake through a coffee stirrer.
If you don’t enlarge the return?
You’ll NEVER have quiet airflow OR strong cooling.
3. Rule #3: Your Duct Size Determines Your BTUs — More Than the Compressor Does
A compressor is strong.
Ductwork is fragile.
Air has to move through:
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trunks
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branches
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boots
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flex runs
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transitions
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grilles
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coils
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returns
Each one steals a little airflow.
Most homes have:
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6" branches that only deliver 60–80 CFM
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supply trunks smaller than 12"
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flex runs that sag and cut airflow by 30–70%
-
cheap stamped registers that reduce airflow by another 20–40%
According to the [HVAC Distribution Friction & Duct Loss Performance Sheet], the AVERAGE home duct system is only capable of handling:
800–1,000 CFM TOTAL
That means:
Your existing ductwork supports only 2–2.5 tons — NOT 3 tons.
This is why so many 3-ton systems underperform.
The compressor isn’t the problem.
The ducts are.
4. Rule #4: The 3.5-Ton Coil Helps — But It Can’t Fix Bad Ducts
Goodman pairing a 3.5-ton coil with a 3-ton condenser is one of the smartest design moves in modern HVAC.
Why?
Because:
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bigger coil = lower static
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lower static = easier airflow
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easier airflow = quieter system
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easier airflow = better SEER2 retention
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easier airflow = fewer freeze-ups
The coil acts like a “pressure relief valve” for the duct system.
BUT…
Even the oversized coil can’t compensate for:
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a 10" return
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a 12" supply trunk
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100 ft of sagging flex
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zero balancing
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one return grille
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high attic heat
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leaky ducts
The [Evaporator Coil Airflow Utilization Efficiency Report] confirms that a coil can only work with the air it receives.
And bad ducts don’t give it enough.
The coil is forgiving.
Your ductwork isn’t.
5. Rule #5: Horizontal Installations Need EVEN MORE Airflow
A horizontal coil (like the CHPTA4230C3) always requires more attention because:
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attic heat makes the coil hotter
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horizontal airflow is harder to distribute evenly
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condensate re-evaporation increases
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coil face velocity must be perfect
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plenum geometry makes or breaks airflow
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longer attic duct runs increase resistance
This is backed by the [Thermal Load Mitigation Paper], which notes airflow loss of:
12–22% in attic installations
due to heat soak, duct insulation aging, and radiant load.
If your home uses attic ducts, you often need:
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larger returns
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larger supply trunks
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fewer flex runs
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more rigid duct
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better balancing
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attic insulation upgrades
Horizontal installs punish weak ductwork.
6. Rule #6: Static Pressure Is the Silent Killer of SEER2 and Quiet Operation
Static pressure is the most misunderstood measurement in HVAC.
Static pressure is basically air resistance inside the ductwork.
Your Goodman system needs:
0.36 – 0.50" WC total external static
Most homes I test sit at:
0.70 – 1.20" WC
That is catastrophic.
The [Residential Static Pressure Diagnostic Case Study] shows that for every 0.10" WC above 0.50, the system loses:
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3–7% efficiency
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10–20% airflow
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5–10% capacity
That means at 0.90 static, your 3-ton system is delivering:
1.5–2 tons of real cooling
This is why people say:
“My house takes forever to cool!”
“My AC never shuts off!”
“My system is loud!”
“It’s only 3 years old — why does it struggle?”
Static.
Pressure.
Kills.
Systems.
7. Rule #7: Duct Leakage = Guaranteed Tonnage Loss
If your ducts leak:
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cold air dumps into the attic
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hot attic air gets pulled into returns
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system loses cooling
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blower ramps up
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coil temperature rises
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humidity skyrockets
The Residential Duct Leakage & Thermal Degradation Field Audit shows:
The average home loses 20–30% of cooling to duct leaks.
Older duct systems?
40–50% loss.
That means a 3-ton system becomes a 1.5-ton in minutes.
Leaks are airflow murder.
8. Rule #8: Even If Everything Else Is Perfect — Bad Grilles Kill Airflow
Most supply grilles (the pretty ones you see in the ceiling/wall) are actually terrible for airflow.
Stamped-face grilles:
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choke airflow
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create turbulence
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increase noise
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increase static pressure
The [Supply Register Free-Area Performance Chart] measured dozens of common registers and found many deliver:
Only 50–60% of the airflow you THINK you’re getting.
That means a 100 CFM duct may only deliver 50–60 CFM into the room.
Multiply that across the whole house, and your 3-ton system is struggling before it even starts.
**9. Mike’s CFM Rules:
Want 3 Tons of Cooling? Here’s the Reality.**
Here are the true, field-tested rules:
✔ Rule 1 — You need 1,200–1,500 CFM
Non-negotiable.
✔ Rule 2 — Return duct must be 14–16" minimum
Smaller = noise + inefficiency.
✔ Rule 3 — Supply trunk must be 14–18"
Anything smaller chokes airflow.
✔ Rule 4 — Keep return velocity under 400 FPM
Lower is quieter.
✔ Rule 5 — Keep static pressure under 0.50" WC
Above that? You’re losing tonnage.
✔ Rule 6 — Fix duct leaks
A 3-ton becomes a 2-ton instantly with leakage.
✔ Rule 7 — Avoid long, sagging flex duct
Rigid duct = better airflow, quieter operation.
✔ Rule 8 — Use oversized grilles
Small grilles crush CFM.
✔ Rule 9 — Horizontal installs need extra airflow
Attic heat and long duct runs demand it.
Follow these rules, and your 3-ton Goodman R-32 system will deliver the full 3 tons of cooling power you paid for.
Ignore them, and your system will never perform — no matter how good the equipment is.
**10. Mike’s Final Verdict:
Your Goodman System Isn’t the Problem — Your Ducts Are**
Here’s the reality HVAC salespeople don’t tell you:
✔ The Goodman condenser is powerful
✔ The Goodman coil is efficient
✔ The R-32 refrigerant cools like a beast
✔ The blower can move plenty of air
But your ductwork decides whether ANY of that matters.
You can ruin a perfect system with bad ducts…
or you can make an average system feel amazing with good ducts.
If you want true 3-ton performance:
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test static
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measure airflow
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upgrade returns
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replace restrictive grilles
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fix or replace ducts
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balance the system
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eliminate flex duct abuse
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seal everything
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cool the attic
Do that, and your system will blow cold, quiet, beautiful air for 15–20 years.
That’s the Mike way.
Now, let's understand the seasonal maintenance for this system in the next blog.
