Climate Zone 1A Sizing Chart: Pick the Right AC for Humid Homes

Let’s start on the porch: why 1A homes feel different

Step outside in Miami or the Gulf Coast and you can feel the air thick, warm, and heavy with moisture. In Climate Zone 1A (very hot-humid), your HVAC isn’t just a cooler; it’s your home’s moisture manager. The right size system keeps temperatures steady and holds indoor humidity near 50%. Go too small and you’ll chase temps all day. Go too big and the system cools fast but doesn’t run long enough to dry the air, leaving rooms clammy. This guide walks you through a practical, story-style plan to pick the right size (2.5–5.5 tons for 1,500–3,000 sq. ft.) and the right features for reliable comfort. We’ll also point you to helpful tools and equipment options so you can make confident, no-nonsense decisions.

Our general Sizing Guide and keep it open as you read.

What “very hot-humid” really means (and why it matters)

Zone 1A brings 9,000+ Cooling Degree Days, sky-high relative humidity (often 74%+), and year-round cooling demand. Heating needs are minimal; the real battle is latent load the moisture your system must remove to keep indoor air healthy and comfortable. In parts of Florida, Texas Gulf Coast, Louisiana, Puerto Rico, and Hawaii, ACs run long and often, and homes can stay muggy unless your system is sized and set up for dehumidification. That’s why our recommendations lean on variable-speed and multi-stage systems, smart controls, and sometimes supplemental dehumidifiers. We’ll translate the engineering into simple steps: how many tons you likely need, what features to prioritize, and which products match those needs.

Quick 1A sizing chart (1,500–3,000 sq. ft.)

Use these Zone-1A-adjusted ranges as a practical starting point (we’ll show how to refine them next):

• 1,500–1,600 sq. ft.: 3.0–3.5 tons (lean high for humidity)

• 1,800–2,000 sq. ft.: 3.5–4.0 tons

• 2,400–2,600 sq. ft.: 4.25–4.75 tons

• 2,800–3,000 sq. ft.: 4.75–5.5 tons

Why is it larger than “rule-of-thumb”? In 1A, you need longer runtimes at lower speeds to pull moisture off the coil. A variable-speed or two-stage unit keeps the coil cold longer so the air dries properly.

• Exploring equipment? See R-32 condensers here and R-32 AC + air handler systems here.

Humidity control > “colder air” (the 1A reality)

Cooling removes sensible heat (temperature) and latent heat (moisture). In 1A, latent load is the bully: systems may need to remove 40–50% more moisture than in dry climates. The fix is time on the coil your system should run longer at lower output, not blast full-tilt and shut off. That’s why we recommend:

• Variable-speed compressors and indoor fans

• Enhanced dehumidification modes (lower fan speeds, smarter staging)

• Smart thermostats that control humidity, not just temperature

If your air feels “cool but sticky,” you likely have oversizing or airflow issues.

The oversizing trap (and how to dodge it)

Oversized systems short-cycle they hit the temp fast, shut off, and don’t dehumidify. That leads to:

• 60%+ indoor RH (feels clammy, invites mold)

• Uneven room temps

• Higher bills from inefficient cyclin

• Wear and tear on parts

How to avoid it:

1. Favor variable-speed or two-stage equipment sized for humidity, not just square footage.

2. Set proper airflow (CFM/ton) and verify static pressure.

3. Use longer fan/coil contact time via dehumidification modes.

4. If needed on larger homes, add a whole-house dehumidifier.

Manual J: the math that pays you back

A Manual J load calculation is the difference between guessing and getting it right. It accounts for:

• Orientation & solar gain (east/west glass can spike loads)

• Insulation & air sealing (tight homes often need smaller systems)

• Window SHGC/U-value & shading

• Occupants, lights, appliances (internal gains)

• Local design temp & humidity

In 1A, Manual J helps size for both sensible and latent loads. It may confirm the chart above or nudge you up/down a half-ton based on your home.

Want a quick path to pro eyes on your numbers? Try our Design Center for help choosing matched equipment: Design Center or get a fast Quote by Photo: Upload photos.

The feature set we trust in 1A

When you’re shopping, prioritize:

• 16+ SEER2 (efficiency for long cooling seasons)

• Variable-speed compressor and indoor blower

• Smart humidity control (thermostat that targets %RH)

• Coastal-grade, corrosion-resistant coils/cabinets if you’re near salt air

• Quiet operation (long, low-speed runs)

• Proper refrigerant charge and matched components

Why we like R-32 in hot-humid climates

R-32 systems are designed for high efficiency and strong performance at higher outdoor temps perfect for 1A. Paired with variable speed and thoughtful airflow, they deliver steady temps and better moisture control without constant full-tilt operation. They also support modern coil designs that withstand demanding run hours. If you’re replacing older equipment, consider a complete matched set (condenser + air handler/coil) for best results.

Upgrading the indoor coil and line set together prevents restrictions and oil issues. See Line Sets.

Ducts, airflow, and the “even room” test

Even the best condenser struggles with leaky or undersized ducts. In 1A, aim for tight ducts, balanced supply/return, and proper CFM/ton (~350–450 CFM/ton, then fine-tune for humidity). Bedrooms and far rooms need measured supply; big returns help systems breathe. If ducts are a mess or space is tight, ductless can be a smart pivot.

• Central components: Air Handlers

• Ductless choices: Mini-Splits (wall, cassette, concealed, floor console)

Ask for a static pressure test at commissioning. High static = noisy vents, low airflow, poor dehumidification.

When to add a whole-house dehumidifier

For homes over 2,000 sq. ft. or with high internal moisture (lots of cooking, showers, large families), a dedicated whole-house dehumidifier can pull 70–100 pints/day and let your AC focus on cooling. It ties into your ductwork, runs when humidity is high, and drops RH faster without overcooling rooms. It’s also a lifesaver during mild but muggy days when the AC doesn’t run much.

• Planning accessories? Browse Accessories.

• Need help deciding size/placement? Visit our Design Center.

Set your dehumidifier target ~50% RH; coordinate with the thermostat so they don’t fight each other.

Real-world 1A scenarios (what we’d recommend)

Scenario A: 1,600 sq. ft. bungalow with average insulation, sun-exposed windows. We’d look at ~3.0–3.5 tons with variable speed and a thermostat that controls %RH. If ducts are tight on space, consider a ductless multi-zone: Wall-Mounted Systems.

Scenario B: 2,000 sq. ft. two-story. Start ~3.5–4.0 tons variable-speed split system and verify returns on both floors.

Scenario C: 2,800–3,000 sq. ft. with open kitchen and big glass. Consider 4.75–5.5 tons total capacity sometimes as two smaller systems or a packaged unit if the layout fits: Packaged Units.