Designing for Humidity Why a 13.4 SEER2 Unit Behaves Differently in Wet vs. Dry Climates

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Jake’s complete guide to moisture load, coil behavior, latent vs. sensible cooling, and why climate matters more than tonnage.

Most homeowners shop for AC systems based on one number:

SEER2.

“Higher SEER2 = better cooling,” right?

Not exactly.

Here’s the truth most people don’t hear:

A 13.4 SEER2 system cools VERY differently depending on how much moisture is in the air.

And if your home is in a humid climate, the performance you get from your AC is determined just as much by moisture load as by heat load.

2.5 Ton Up To 15 SEER2 Goodman Air Conditioner Model - GLXS3BN3010

That’s why a 13.4 SEER2 system in:

Florida feels different than
Arizona, and both behave differently than
Tennessee, Georgia, or Utah

This guide breaks down exactly how humidity changes AC behavior, why modern SEER2 systems behave differently, and what homeowners must do to get the comfort they actually paid for.

Let’s get into the science—and the real-world fixes.

🧠 1. Sensible vs. Latent Cooling — The Key to Understanding Humidity

There are two types of cooling:

1️⃣ Sensible Cooling (temperature drop)

This is the cooling you feel on a thermostat.
It lowers air temperature.

2️⃣ Latent Cooling (moisture removal)

This removes humidity from the air.
It makes the air feel lighter, cleaner, drier, and cooler.

ASHRAE defines these as the two fundamental components of total cooling load:
ASHRAE Sensible & Latent Heat Fundamentals
https://www.ashrae.org

Dry climates = mostly sensible load

Think: Phoenix, Las Vegas.

Humid climates = heavy latent load

Think: Houston, Miami, New Orleans.

Why does this matter?

Because a 13.4 SEER2 unit is optimized for sensible efficiency, not necessarily humidity removal.

🌡️ 2. Why SEER2 Systems Struggle More in Humid Climates

SEER2 testing is performed under specific conditions that don’t reflect high-humidity environments.

ENERGY STAR explains that humidity is NOT included in SEER2 rating tests:
ENERGY STAR Cooling Efficiency Standards
https://www.energystar.gov

Here’s why this matters:

In dry climates:

A 13.4 SEER2 AC approaches its full efficiency.

In humid climates:

The same AC must work harder because latent cooling (water removal) is energy intensive.

Every pint of water removed from the air requires additional compressor energy.

Humid states force the AC to:

run longer
run colder coil temps
cycle differently
deliver less “felt cooling”

Even though it’s the same unit.

💦 3. The Hidden Number Homeowners Never Hear About: SHR

The Sensible Heat Ratio (SHR) tells you how much of an AC’s cooling goes to air temperature vs. humidity.

High SHR = more temperature drop, less water removal

Common in dry climates

Low SHR = more moisture removal, less temperature drop

Needed in humid climates

A typical 13.4 SEER2 system has an SHR of 0.75–0.80.
Meaning:

75–80% of cooling = temperature
20–25% = humidity removal

In a dry climate, that’s great.
In a wet climate, that’s limiting.

If humidity removal is insufficient, you get:

sticky rooms
swampy air
“cool but damp” feeling
mold-friendly conditions
poor sleep quality

The EPA warns that homes above 60% humidity rapidly increase mold risk:
EPA Indoor Relative Humidity Guidance
https://www.epa.gov/mold

Even a correctly sized AC can fail if the latent load is too high.

🌍 4. How R-32 Refrigerant Changes Humidity Behavior

R-32—now common in many 13.4 SEER2 units—has different cooling characteristics:

✔ Faster heat absorption

✔ Higher discharge temperature

✔ Lower refrigerant mass

✔ Higher vapor density

✔ Better efficiency at higher outdoor temps

Daikin’s R-32 research highlights these differences: Daikin R-32 Refrigerant Overview

What does this mean for humidity?

R-32 systems respond faster, but also lose coil temperature faster when airflow is high.

In a dry climate, this creates crisp, efficient cooling.

In a humid climate, this can cause:

shorter run cycles
less moisture removal
higher indoor humidity

This is why climate-based design is critical with SEER2 + R-32 systems.

🔥 5. Why Short Cycling Destroys Humidity Control

Short cycling = AC turns on and off quickly.

This is fatal for humidity removal because moisture extraction only happens when:

the coil is cold enough
long enough
to condense water vapor out of the air

Short run times = minimal condensation.

Causes of short cycling include:

oversized AC
undersized ductwork
high airflow
leaky returns
thermostat location problems
humidity-based load mismatches

If your AC cools your home in 5–10 minutes, it’s too powerful for humid climates.

Jake’s rule:

**Dry climate → fast cycles OK

Humid climate → long cycles required**

❄️ 6. Wet vs. Dry Climate Airflow Requirements

Dry climate airflow:

400–450 CFM per ton

Why?
Fast airflow across the coil = rapid temperature drop.

Humid climate airflow:

325–375 CFM per ton

Why?
Slower airflow = colder coil = more moisture removal.

ACCA supports lowered airflow for better dehumidification in wet climates: ACCA Manual S – Equipment Selection

Jake always reduces blower speed in humid regions after confirming static pressure.

🧊 7. Coil Temperature: The Silent Player in Moisture Control

Coils must reach ~45–50°F to pull moisture out of the air.

Your 13.4 SEER2 unit may struggle to reach this coil temperature if:

❌ airflow is too high

❌ ducts are undersized

❌ return air is too warm

❌ the attic is superheated

❌ the system is oversized

❌ the TXV is mismatched

A hot, wet climate pushes indoor humidity into the ducts.
If ducts leak, return air warms up.
Coil temp rises.
Moisture removal stops.

This is why homes in:

Florida
Georgia
Alabama
Texas
South Carolina

often feel clammy even when cool.

🌡️ 8. Humidity Makes Your AC Feel “Weak” Even When It’s Working

If humidity is 60–75% indoors, your AC will feel like it’s underperforming because:

Moist air feels warmer than dry air.

This is psychrometrics—the science of air properties.

According to ASHRAE psychrometric charts: ASHRAE Psychrometrics

Air at:

75°F @ 40% RH = comfortable
75°F @ 70% RH = feels like 82–84°F

That’s a 7–9° perceived increase.

So even if your SEER2 unit is cooling perfectly…
…it still feels warm because humidity is too high.

📝 9. The 6 Big Risks of Using a 13.4 SEER2 AC in a Humid Climate Without Proper Design

1. Mold Growth

Humidity > 60% becomes mold-friendly.

2. Dust Mites Increase

Ideal dust mite humidity is 70–80%.

3. “Wet Sock Syndrome” Odor

Occurs when coils stay wet too long.

4. Comfort Drops Dramatically

Humidity robs temperature of its cooling effect.

5. Higher Energy Bills

System runs longer trying to dehumidify.

6. Shortened Equipment Life

Humidity stresses both coils and blowers.

🛠️ 10. Jake’s Wet Climate Design Strategy for 13.4 SEER2 Units

To get maximum comfort in humid states, Jake does the following:

1. Reduce Airflow (After Static Pressure Check)

Drop to 325–375 CFM/ton.

2. Ensure Proper TXV / Coil Matching

R-32 systems are VERY sensitive to mismatched coils.

3. Improve Return Duct Sizing

Return air must breathe easily.
High static pressure kills dehumidification.

4. Seal Duct Leaks

Especially in attics where humid air infiltrates.

5. Add a Whole-Home Dehumidifier (Best Fix)

Ideal for Gulf Coast states.

6. Increase Runtime

Sometimes via:

longer fan-off delay
humidity-based staging
smart thermostat tuning

🪭 11. Jake’s Dry Climate Design Strategy for 13.4 SEER2 Units

Dry climates want maximum sensible cooling.

So Jake increases:

✔ airflow (400–450 CFM per ton)

✔ condenser placement airflow

✔ blower speed curves

✔ duct size for high-volume airflow

Humidity removal is not the priority.

Rapid temperature reduction is.

📊 12. Comparing Real-World Behavior: Humid vs. Dry Climate Performance

Feature	Wet Climate (FL, GA, TX)	Dry Climate (AZ, NV, NM)
Ideal Airflow	325–375 CFM/ton	400–450 CFM/ton
Runtime	Longer needed	Shorter cycles
Coil Temp	Must be lower	Can be higher
Comfort Factor	Affected by humidity	Affected by radiant heat
Risk	Mold, clammy air	Hot rooms, dry sinuses
Design Priority	Latent cooling	Sensible cooling