R-32 is shaking up the HVAC world. It’s more efficient, lower-GWP, easier to charge accurately, and gives homeowners cooler air using less energy. But Mike Sanders will tell you the real truth:
“You don’t get R-32 performance unless your ductwork is ready for it.”
The refrigerant, the coil, the blower, and the duct system operate as one machine. And when you drop next-gen refrigerant technology into old ducts built for R-22 or R-410A systems, you’re mixing modern efficiency with 20-year-old airflow math.
That’s where Mike’s R-32 Integration Matrix comes in — a ruleset he uses to adapt legacy duct systems to modern refrigerant performance requirements, ensuring the home actually sees the efficiency R-32 is capable of delivering.
This article gives you the full blueprint.
📘 1. Why R-32 Systems Behave Differently Than R-410A
Before you match any next-gen equipment to old ducts, you need to understand why R-32 behaves differently.
🧊 1.1 Higher Volumetric Efficiency
R-32 carries more heat per pound than R-410A — roughly 10%–12% more thermal capacity.
This means:
-
Faster heat transfer
-
Higher coil performance
-
Lower refrigerant mass flow
-
More efficient compressor operation
But also:
-
Coil saturation happens faster
-
Blower speed becomes more sensitive
-
Poor ducts choke performance faster than before
External Link: Basic R-32 vs R-410A comparisons
🔥 1.2 Higher Discharge Temperatures
R-32 compressors run at higher discharge temps, which impacts:
-
TXV behavior
-
Coil temperature splits
-
Sensible cooling ratios
In a restrictive duct system, higher discharge temps can force the compressor into shorter cycles, tanking efficiency.
🌡️ 1.3 Faster Coil Response = Less Room for Airflow Mistakes
R-32 systems have faster evaporator coil reactions — meaning:
-
Undersized ducts → coil freezes sooner
-
Oversized ducts → lower coil temperature split
-
Bad return paths → pressure imbalance faster
This makes R-32 far less tolerant of old ductwork problems.
🗂️ 2. Mike’s Integration Matrix: The Four Pillars of R-32 Compatibility
Mike’s entire approach comes down to four pillars:
🌀 Pillar 1: Static Pressure Control
R-32 systems need lower total external static pressure than older systems.
Ideal: 0.4–0.5 inWC total ESP for most 3–5 ton systems.
Legacy duct systems often hit 0.7–0.9 inWC—or worse.
🔍 Mike’s Rules:
-
If ESP exceeds 0.6, R-32 performance drops by 15–30%.
-
If ESP exceeds 0.8, the system loses SEER2 efficiency entirely.
-
Tight ducts must be enlarged, not “balanced.”
🚫 What Mike Never Does:
“I never install a variable-speed R-32 system on legacy 6-inch supplies alone.”
Most older homes have:
-
6" supply runs
-
Undersized returns
-
Flex duct with sag
-
Sharp-elbow takeoffs
All of which kill airflow.
🔄 Pillar 2: Return Air Capacity
R-32 systems REQUIRE high return air volume because the coil works harder.
🧮 Mike’s Return Air Rule:
Every ton of cooling requires 350–425 CFM — and that airflow must actually reach the coil.
Mike’s Return Rules:
-
Minimum 1 sq in per 1 CFM for filter area
-
No single return may serve more than 900 CFM
-
Homes with closed-door bedrooms must have jumper ducts or transfer grilles
-
Return air must be within 25 ft of the air handler for 4+ ton systems
Why this matters:
R-32 evaporator coils produce stronger negative pressure on the return side.
Weak returns = starved coil = short cycling + poor humidity control.
External Link: EPA guidelines on airflow & return sizing
🚚 Pillar 3: Duct Travel Distance Limits
R-32 systems hate long duct runs.
Mike’s Rule:
No individual branch should exceed 25–30 linear feet for a 4–5 ton system.
Anything longer must be:
-
upsized
-
re-routed
-
or split into two branches
Why?
Long runs = friction loss
Friction loss = reduced CFM
Reduced CFM = coil freezes faster
Legacy systems commonly have:
-
40–50 ft attic runs
-
Compressed flex duct
-
90° hard elbows
These choke R-32 coils immediately.
❄️ Pillar 4: Coil & Blower Synchronization
R-32 systems often use:
-
optimized evaporator coils
-
larger fin density
-
higher SUCTION pressure requirements
-
more aggressive TXVs
The blower must be tuned exactly right to match coil behavior.
Mike’s Coil-Blower Rules:
-
If coil is oversized, blower must ramp slower
-
If coil is undersized, blower must ramp faster
-
Always use TXV or EEV on R-32 systems
-
Never rely on piston metering devices in retrofits
External Link: ASHRAE refrigerant design standards
🧱 3. What Legacy Ductwork Does Wrong With R-32
Mike has seen this hundreds of times:
“The homeowner buys a fancy new system, but the old ducts force it to run like a 15-year-old unit.”
Here’s where old duct systems fail the most.
🟥 3.1 Undersized Supply Trunks
A 4-ton system should have:
-
18–20" main trunk
-
14–16" secondary trunks
Legacy systems often have:
-
14" trunks for 4–5 ton units
-
Bottlenecked wyes
-
Mismatched trunk insulation
This can cut system CFM by 40%.
🟥 3.2 Undersized Returns
A 4-ton unit requires 1600 CFM minimum.
Legacy returns often supply only 900–1200 CFM.
R-32 coils starve instantly.
🟥 3.3 Flex Duct That Is Sagging or Crushed
Mike calls this “the silent killer.”
A flex run sagging only ½ inch per foot reduces airflow by:
-
8–12% over 20–25 ft
-
20–30% with two bends
-
30–50% with attic heat
🟥 3.4 Leaky Ducts in Attics
Attic duct leakage causes:
-
20–30% loss in delivered BTUs
-
Higher heat gain
-
Return air pulling in 140°F attic air
External Link: Duct leakage & energy losses
🟥 3.5 Wrong Filter Rack Geometry
Older systems often used:
-
1" filters
-
Undersized filter grilles
-
Poor sealing
R-32 systems need MERV 8–11 at low pressure drop.
1" filters often add 0.20–0.25 inWC to static pressure — which is unacceptable.
🏗️ 4. Mike’s Retrofit Framework: Upgrading Old Ducts for R-32
This is Mike’s actual checklist when retrofitting next-gen refrigerant systems into legacy homes.
🔧 Step 1: Measure Total Static Pressure
Mike uses a manometer to measure:
-
Return static
-
Supply static
-
TESP (total external static pressure)
Good: 0.30–0.50
Acceptable: 0.50–0.60
Bad: 0.60–0.80
Fail: 0.80+
If ESP > 0.6, he starts correcting immediately.
🔧 Step 2: Fix the Returns First
For 4–5 ton units:
-
Add dedicated return to master bedroom
-
Add 2nd story return
-
Add jumper ducts for closed-door rooms
-
Switch to 2" or 4" media filter cabinets
-
Replace closets with air-tight return enclosures
Return centric design is the MOST important part of R-32 retrofits.
🔧 Step 3: Resize Critical Supply Branches
Mike upsizes:
-
6" → 7"
-
7" → 8"
-
8" → 10"
Especially for:
-
long runs
-
rooms with high solar load
-
2nd-floor zones
He also removes:
-
sharp elbows
-
unnecessary wyes
-
kinked flex
🔧 Step 4: Correct Duct Leakage
He seals ducts with:
-
mastic
-
foil tape
-
aerosol duct sealing if extreme
Goal: <10% leakage
Old ducts often leak 20–40%.
🔧 Step 5: Clamp Down on Attic Heat Transfer
Mike reinsulates:
-
supply trunks
-
return trunks
-
branch ducts
Target: R-8 insulation minimum for attics.
🔧 Step 6: Tune the Blower to the Coil
Variables include:
-
coil tonnage
-
blower motor (ECM vs PSC)
-
duct size
-
return capacity
Mike uses static pressure targets and temperature splits to dial blower speed to match the coil’s optimal evaporating temperature.
External Link: Goodman / Daikin R-32 engineering specs
https://www.goodmanmfg.com
📊 5. Real-World Case Study: Mike’s R-32 Duct Retrofit Formula
Home: 2,800 sq ft two-story
Original Ducts: 1998 R-22 system
New System: 4-ton Goodman R-32 14.5 SEER2
Problems:
-
high static pressure (0.82)
-
hot 2nd floor
-
low humidity removal
-
noisy airflow
-
compressor short cycling
Mike’s Fixes:
-
Added 2nd return upstairs
-
Upgraded 1" filter to 4" media cabinet
-
Upsized three 6" ducts to 8"
-
Removed two 90° elbows
-
Reinsulated attic duct trunks to R-8
-
Added jumper ducts to bedrooms
-
Balanced blower speed from 75% to 65%
Result:
-
Static pressure dropped to 0.47
-
Upstairs temps evened out
-
Compressor cycles stabilized
-
18–22% lower energy consumption
-
35% better humidity control
THIS is what proper R-32 pairing looks like.
🧠 6. Mike’s R-32 Retrofit Rules (Quick List)
✔️ Rule 1: Fix returns before supplies
✔️ Rule 2: 4-ton = minimum 1600 CFM delivered
✔️ Rule 3: No branch run >30 ft
✔️ Rule 4: Always upgrade filter racks
✔️ Rule 5: Aim for ≤0.5 inWC total static pressure
✔️ Rule 6: Seal all ducts in unconditioned spaces
✔️ Rule 7: Match blower speed to coil tonnage
✔️ Rule 8: Use TXV/EEV — no piston metering
✔️ Rule 9: Add jumper ducts for closed-door rooms
✔️ Rule 10: Replace sagging flex duct immediately
Follow these rules and R-32 will perform at the efficiency levels promised on paper.
Ignore them, and your “efficient system” will run like a 2006 R-410A unit.
🎯 Final Takeaway: R-32 Performance Lives or Dies by Ductwork
Mike Sanders says it best:
“R-32 isn’t magic. It’s a high-output refrigerant that needs high-capacity airflow. Give it good ducts, and it’ll outperform anything you’ve ever installed.”
The R-32 Integration Matrix is all about respecting how advanced these systems are — and how outdated most duct systems in American homes have become.
