Sensible vs. Latent Load: Why Humidity Matters in HVAC

There are two completely different types of cooling happening in your home. If you confuse them, you'll end up with a cold house that's still humid—or worse, an AC that can't keep up.

The Two Types of Cooling

Sensible Load: Cooling the air temperature. (Thermometer goes down.)
Latent Load: Removing moisture from the air. (Humidity goes down.)

Your AC has to handle both. If it only handles one, you'll be uncomfortable.

The Physics: How Air Conditioners Work

An air conditioner works by running refrigerant through an evaporator coil. The coil gets very cold (usually 40-50°F). When warm, humid air from your home passes over this cold coil, two things happen:

The air cools down. Heat is removed from the air and carried away by the refrigerant. This is sensible cooling.
Moisture condenses on the coil. Like water droplets forming on a cold window, moisture in the air condenses into liquid water on the cold coil. This water drains away. This is latent cooling.

Both happen simultaneously. But the balance between them depends on your home's humidity level.

Sensible Load: Cooling the Air Temperature

Sensible load is the cooling capacity needed to lower the air temperature from outside (108°F in Phoenix) to your desired inside temperature (72°F).

In dry climates like Phoenix or Denver, sensible load is the dominant factor. The air is so dry that latent cooling is almost negligible.

Phoenix: Desert Climate

Outside: 108°F, 20% humidity
Inside: 72°F, 50% humidity
Sensible: 90% of cooling
Latent: 10% of cooling

Miami: Humid Climate

Outside: 91°F, 80% humidity
Inside: 72°F, 50% humidity
Sensible: 60% of cooling
Latent: 40% of cooling

Notice the difference? In Miami, 40% of your AC's cooling capacity is being used just to remove moisture, not cool the air. This is why Miami needs a proportionally larger AC than a desert city with the same temperature.

Latent Load: Removing Humidity

Latent load is the cooling capacity needed to condense and remove water vapor from the air.

In humid climates, this is massive. The outside air in Miami in summer can have an absolute humidity of 180 grains per pound of dry air. Your AC has to pull all that moisture out.

Why Undersized ACs Cause Humidity Problems

Remember the short-cycling problem we mentioned in the 500 Sq Ft Rule article?

An undersized AC in a humid climate is even worse because:

It runs constantly trying to remove heat, but never reaches the desired temperature.
It doesn't get cold enough to dehumidify. The coil never gets cold enough to condense significant moisture. The air gets cooler but stays humid.
Result: Cold, clammy, uncomfortable home. Mold risk. The AC is overworked and fails early.

Why Oversized ACs Cause Humidity Problems (Again)

Ironically, oversized ACs also fail to dehumidify properly. Here's why:

It cools too fast. An oversized AC reaches the desired temperature in 10 minutes and shuts off.
The coil doesn't run long enough. It takes about 15 minutes of continuous operation for the coil to get cold enough and stay cold enough to pull significant moisture.
Result: The house feels cold but clammy. You're uncomfortable even though the thermometer says 72°F.

This is why proper sizing is critical in humid climates. You need enough capacity to handle both sensible and latent loads, and the AC needs to run long enough to dehumidify.

How to Account for Latent Load

Latent load depends on:

Outside Humidity

Measured as wet bulb temperature. Miami: 77°F. Phoenix: 50°F. Higher wet bulb = higher latent load.

Desired Inside Humidity

Most homeowners want 45-55% relative humidity. Florida might struggle to reach 50% due to outside humidity.

Air Infiltration

Leaky homes bring in more humid outside air. Air sealing reduces latent load.

Internal Moisture Sources

Showers, cooking, washing clothes. More people = more moisture.

A proper Manual J calculation accounts for all these factors. A rough rule of thumb: In humid climates, add 10-30% to your sensible load to cover latent load.

Real-World Scenario: Why Florida Homeowners Suffer

The Miami Problem

A 2,500 sq ft home in Miami with typical 1970s construction. Contractor uses the old "500 sq ft rule."

Rule of Thumb Calculation:

2,500 sq ft ÷ 500 = 5 tons

Manual J (Proper Calculation):

Sensible load: 3.2 tons
Latent load: 1.8 tons
Total: 5 tons (happens to match!)

But Here's the Problem:

The 5-ton AC was sized for average conditions. On the wettest day (80°F outside, 90% humidity), the latent load skyrockets. The AC can't keep up. Result: AC runs 24/7 and home feels sticky.

This is why our calculator includes a humidity factor based on your climate data. Miami, Houston, and New Orleans get higher latent load factors than Phoenix or Denver.

The Takeaway

Never ignore latent load. It's not just a number—it's the difference between:

Feeling comfortable all summer
Feeling cold and sticky despite the AC running
Preventing mold and water damage
Having an AC that lasts 15 years instead of failing in 8

If you live in a humid climate, your AC sizing must account for latent load. Period.

Sensible vs. Latent Load
Why Your AC Can Cool But Still Feel Sticky