🌡️ Introduction: Two Numbers That Make or Break Your System
Most installers talk about tonnage, SEER2, and BTUs like they’re the only things that matter.
Tony? No way.
He says every HVAC system lives or dies by two numbers:
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Heat Rise (heating performance)
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Temperature Split / ΔT (cooling performance)
These two numbers tell Tony instantly whether the blower speed is right, the airflow is right, and the system is delivering what the homeowner paid for.
Yet 90% of installations get blower speeds wrong.
Tony’s line:
“Your blower speed is the gas pedal. If you floor it or feather it without understanding heat rise and temp split, the system dies early — or the customer hates the comfort.”
This is the war that happens inside every HVAC system: Too much airflow kills heat rise. Too little airflow kills cooling temp split. And a bad installer kills both.
This article breaks down Tony’s field-tested process for balancing heat rise vs. temperature split in the age of SEER2.
3 Ton 15.2 SEER2 80,000 BTU 96% AFUE Goodman Upflow Air Conditioner System
🔥 1. What Heat Rise Actually Measures — And Why It’s Your Furnace’s Lifeline
Heat Rise = Supply Air Temp − Return Air Temp (Heating Mode)
It tells Tony how much the furnace is increasing the temperature of the air as it moves through the heat exchanger.
Typical manufacturer spec for a modern gas furnace:
40°F to 70°F
(e.g., a 96% Goodman furnace)
If heat rise is too high:
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The heat exchanger overheats
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The limit switch trips
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The blower motor strains
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The furnace short cycles
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Efficiency drops
If heat rise is too low:
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Furnace blows lukewarm air
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Vents feel cold
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Customers complain instantly
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Condensation forms where it shouldn’t
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Heat exchanger lifespan drops
Tony’s phrase:
“Heat rise tells me if the furnace is happy, angry, or dying.”
✔️ Verified reference on heat rise fundamentals: https://www.goodmanmfg.com
❄️ 2. What Temperature Split (ΔT) Measures — And Why It’s the Truth Detector in Cooling Mode
Temperature Split = Return Air Temp − Supply Air Temp (Cooling Mode)
This number tells Tony whether the evaporator coil is removing enough heat — and whether the airflow is right for cooling.
Ideal temp split:
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18°F to 22°F for most 3-ton SEER2 systems
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20–24°F in humid climates
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16–18°F in extremely dry climates
If ΔT is too low (<16°F):
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Airflow too high
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Coil is too warm
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Poor dehumidification
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Higher humidity
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Higher bills
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Short cycling in mild weather
If ΔT is too high (>24°F):
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Airflow too low
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Coil too cold
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Risk of freeze
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Liquid floodback to compressor
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Refrigerant charge misdiagnosis
Tony’s favorite quote:
“If temp split is wrong, start with airflow — not refrigerant.”
✔️ Coil performance & ΔT reference: https://www.ahridirectory.org
🥊 3. The Hidden War: Heat Rise vs. Temperature Split
Here’s the battle installers never talk about:
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Heating wants LOWER airflow → HIGHER heat rise
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Cooling wants HIGHER airflow → LOWER temperature split
The blower must do both, not just one.
Service mistake Tony sees constantly:
Installers choose one of these three bad habits:
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Use the factory default blower tap
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Set blower for cooling only
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Set blower for heating only
All three lead to callbacks — and Tony happily takes their money fixing it.
🧪 4. How SEER2 Made Blower Speeds Even Harder to Set
SEER2 coils are more restrictive.
Static pressure is higher.
Duct systems fail sooner.
Filter cabinets choke airflow.
Blower tables changed.
That means:
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Old airflow rules (400 CFM/ton) don’t work in many homes
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Factory blower settings almost never work now
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Most 3-ton systems deliver 20–30% less actual airflow than older systems
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Heat rise skyrockets
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Temperature split swings wildly
Tony explains:
“SEER2 units fight you. If you don’t measure static pressure, your blower speeds are guaranteed wrong.”
✔️ SEER2 technical documentation: https://www.energy.gov
📏 5. The Right Way to Choose Blower Speeds (Tony’s Method)
Tony’s method is simple but deadly accurate.
He doesn’t guess.
He measures the system, then adjusts airflow based on actual live readings — not marketing charts.
Here’s his sequence.
🧰 Step 1 — Measure Total External Static Pressure
Before Tony touches blower taps, he checks:
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Filter
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Coil
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Duct system
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Return drop
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Supply plenum
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Flex runs
Then he measures:
Return Static + Supply Static = TESP
Tony’s static thresholds:
| TESP | System Health |
|---|---|
| 0.3–0.5 | Excellent |
| 0.6 | Acceptable |
| 0.7–0.8 | Warning |
| 0.9+ | Failure |
If static is above 0.7, Tony says:
“You don’t have a blower setting problem — you have an airflow restriction problem.”
✔️ Static pressure reference: https://www.acca.org
💨 Step 2 — Pick Cooling Airflow Target
Tony sets cooling airflow FIRST because SEER2 coils demand specific CFM.
3-Ton Cooling Airflow Targets (Tony’s Rules)
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Dry climate: 400–425 CFM/ton (1,200–1,275 CFM)
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Mixed climate: 375–400 CFM/ton (1,125–1,200 CFM)
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Humid climate: 325–350 CFM/ton (975–1,050 CFM)
Why lower airflow in humid regions?
Because slower air across the coil increases latent removal.
Tony’s words:
“If you live in Florida or Louisiana, 400 CFM/ton is a disaster.”
🔥 Step 3 — Check Heat Rise on That Cooling Airflow Setting
Here’s where 99% of installers get it wrong.
Most will set cooling airflow and walk away.
Tony measures heat rise while the blower is still on that cooling CFM.
Example:
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Goodman 96% furnace
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Heat rise listed: 35–65°F
If the furnace produces:
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70°F rise → Airflow TOO LOW
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Fix: Increase blower speed for heating mode
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30°F rise → Airflow TOO HIGH
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Fix: Slow blower in heating mode
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Tony tunes the furnace to hit the MIDDLE of its rated rise range.
🚦 Step 4 — Create Different Airflow Profiles for Heating vs. Cooling
This is the magic step almost nobody does.
Tony does not use one airflow setting year-round.
Instead, he programs:
Cooling Mode:
Lower ESP → Higher airflow
Heating Mode:
Higher static → Lower airflow
Most modern ECM blowers allow two independent airflow tables:
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Y1 = Cooling
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W1/W2 = Heating
Tony uses them separately.
Because he says:
“Heating airflow and cooling airflow are NOT the same animal. Treating them the same is bad design.”
❄️🔥 6. What Happens When Blower Speed Is Wrong in Cooling Mode
A. Airflow Too High
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Low ΔT
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Coil runs warm
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Humidity stays high
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Rooms feel sticky
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AC runs nonstop
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Poor dehumidification
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Sweating ducts
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High energy bills
B. Airflow Too Low
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ΔT too high
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Coil gets too cold
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Frost forming
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Evaporator freeze
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Liquid floodback
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Compressor damage
Tony’s line:
“Any fool can get cold air. The real pros get the right split.”
🔥🌬️ 7. What Happens When Blower Speed Is Wrong in Heating Mode
A. Airflow Too Low
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Heat rise too high
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Limit switch trips
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Furnace short cycles
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Heat exchanger stress
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Burners shut down
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Reduced furnace life
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Customer feels ‘cold-blow’ between cycles
B. Airflow Too High
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Heat rise too low
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Vents feel lukewarm
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Rooms heat unevenly
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IAQ worsens due to low coil temperature
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Furnace efficiency suffers
Tony says:
“You know you set heat rise wrong when the homeowner says the heat turns on but the vents feel cold.”
✔️ Furnace heat rise reference: https://www.goodmanmfg.com
📡 8. Why Heat Rise Affects Cooling (and Vice Versa)
This is where the war becomes real.
The blower setting you choose for cooling affects:
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Duct pressure
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Motor torque
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Heat exchanger performance
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Coil temperature
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Return air mixing
And the blower setting for heating affects:
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Cooling charge accuracy
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Coil latent capacity
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Summer humidity
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Temperature split
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Fan ramp performance
Blower speed is the bridge between both worlds.
Tony’s golden rule:
“Temperature split lies if heat rise is wrong. Heat rise lies if temp split is wrong.”
🧩 9. Why Most Installers Guess — and Why Tony Never Does
Most installers:
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Never measure static pressure
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Never measure ΔT
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Never measure heat rise
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Never read blower tables
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Never adjust heating vs. cooling CFM
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Leave blower on ‘Factory Auto’ or ‘High’
Because it works “good enough.”
But Tony’s installs last decades and deliver perfect comfort.
Why?
Because he measures EVERYTHING.
“You need instruments — not instincts — to set blower speed.”
✔️ EPA indoor air quality & airflow guidance: https://www.epa.gov/indoor-air-quality-iaq
🧠 10. Tony’s Real-World Example: Fixing a 96% Furnace & 3-Ton SEER2 Coil
Customer complaint:
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AC runs constantly
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Humidity always 62–67%
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Heat feels “weak”
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Rooms never fully warm
Tony tests:
Cooling mode:
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ΔT = 14°F (way too low)
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Airflow too high
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Humidity out of control
Heating mode:
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Heat rise = 72°F (above spec)
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Airflow too low
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Limit switch cycling
Both modes were wrong because the installer left blower on single-speed auto.
Tony’s corrections:
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Lowered cooling airflow (mixed climate → 350 CFM/ton)
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Raised heating airflow
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Corrected static by enlarging return drop
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Added 4" filter cabinet
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Reset refrigerant charge after airflow tuning
Final numbers:
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ΔT = 20°F
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Heat rise = 49°F
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Static = 0.49 in. w.c.
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Humidity = 48–52%
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Comfort = flawless
Tony’s summary:
“The equipment wasn’t broken — the installer just never tuned the blower for the real world.”
🏁 Conclusion: Tune the Blower, Win the War
Heat rise and temperature split are not two random numbers — they’re the core of proper HVAC system design.
They reveal:
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Airflow problems
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Static pressure issues
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Coil performance
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Furnace health
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Humidity control
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Comfort level
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Efficiency losses
But only if the blower speed is set correctly.
Tony’s final words on the topic:
“Blower speed isn’t an option. It’s the foundation.
Get it wrong and the whole system is wrong.”
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In the next topic we will know more about: Why Your Thermostat Location Makes or Breaks Efficiency — Tony’s Field Rules for Sensor Placement
