The Florida Problem:
Why Miami Needs More Than Just "Cooling"

Ask anyone who's visited both Phoenix and Miami in summer, and they'll tell you the same thing: Miami feels hotter, even though the thermometer says otherwise.

Phoenix regularly hits 110°F+, yet people say, "It's a dry heat." Miami tops out around 92°F, but stepping outside feels like walking into a wet towel. This isn't just perception—it's physics. And it completely changes how you size an air conditioner.

The Two Types of Heat Your AC Must Remove

Most homeowners think an air conditioner just "makes cold air." In reality, it removes two distinct types of heat:

In dry climates like Phoenix, sensible heat dominates. Your AC spends 85-90% of its energy just cooling the air temperature.

In humid climates like Miami, latent heat is massive. Your AC must dedicate 25-35% of its capacity to wringing moisture out of the air. This is why Miami's "cooler" 91°F requires just as much tonnage as Phoenix's 111°F.

The Wet Bulb Temperature: The Real Villain

When HVAC engineers size a system, they don't just look at the Dry Bulb Temperature (what your weather app shows). They also check the Wet Bulb Temperature—a measurement that accounts for humidity.

Here's how it works: wrap a wet cloth around a thermometer and wave it in the air. Evaporation cools the thermometer. In dry air, evaporation is fast, so the wet bulb reading drops significantly. In humid air, evaporation is slow, so the wet bulb stays close to the dry bulb.

Compare this to Phoenix:

• Dry Bulb: 111°F
• Wet Bulb: 68°F
• Depression: 43°F (huge gap = bone dry)

Phoenix's massive wet bulb depression means evaporation happens easily. Your sweat works. Evaporative coolers (swamp coolers) work. And your AC coils shed moisture quickly.

Miami's tiny 14°F depression means the air is a sponge that's already soaked. Your AC must work much harder to condense water vapor, and it takes longer to do it.

Why This Destroys the "Square Footage Rule"

The old "500 sq ft per ton" rule assumes a sensible-only load. It was invented in the 1970s for moderate climates (think: Ohio, not Florida).

But in Miami, a significant chunk of your cooling load is invisible. Let's break down a real example:

Notice how Miami's sensible load is actually lower than Phoenix (because 91°F vs. 111°F), but the latent load more than makes up for it. The total tonnage ends up nearly identical.

This is why you can't just copy an HVAC system from Arizona to Florida. The equipment must be optimized for different work.

The "Clammy House" Syndrome

Here's the most common mistake in Florida HVAC: oversizing the unit.

A contractor looks at your 2,000 sq ft home, applies the "500 sq ft rule," and installs a 4-ton unit. On paper, this seems safe—maybe even generous.

But here's what happens:

This is why Florida homes often have that musty, damp smell. It's not mold (yet)—it's an oversized AC that can't do its second job: removing moisture.

How to Size AC Correctly in High-Humidity Climates

In Florida, you need to prioritize runtime over raw capacity. Here's what that means:

Our Miami-specific HVAC calculator automatically adjusts for this. When you enter a Miami zip code, it:

• Pulls the 77°F wet bulb temperature from ASHRAE data
• Calculates a latent load multiplier (typically 0.25-0.35 for Florida)
• Adds this to the sensible load to get your true total tonnage
• Recommends slightly undersizing (by 5-10%) to ensure longer runtimes

Should You Add a Dehumidifier?

In extreme cases—especially in newer, super-insulated homes—you might need a dedicated whole-home dehumidifier.

Here's the paradox: modern homes are so well-insulated that the sensible load (temperature) is tiny. Your AC might only need to run 10 minutes per hour to maintain 75°F. But that's not enough runtime to remove moisture.

Miami vs. Other Florida Cities

Not all of Florida is created equal. Coastal cities have higher wet bulb temperatures than inland areas:

*Data from ASHRAE climate stations. Coastal cities have consistently higher wet bulb temps due to ocean moisture.

The Bottom Line: It's Not Just About Temperature

If you're sizing HVAC in Miami (or anywhere in Florida), you cannot ignore humidity. The "feels like" temperature on your weather app is closer to reality than the actual temperature.

Don't let a contractor size your system based on square footage alone. Demand a calculation that includes your zip code's wet bulb temperature. In Florida, that number matters more than the thermometer reading.