Everything you need to know about choosing, installing, and configuring smart thermostats in high-humidity environments like South Florida. Default factory settings are optimized for moderate climates — this guide covers the adjustments that actually save money and prevent mold in subtropical heat.
Maintained by AC Repair Today — Licensed Florida HVAC Contractor (CAC1824118)
Smart thermostats promise 10-15% energy savings, but those numbers come from Department of Energy studies conducted in temperate climates. In South Florida's heat and humidity, default settings cause three common problems:
- Humidity creep — Default target of 60% RH is too high. Above 55%, mold growth accelerates on walls, in ducts, and behind furniture
- Aggressive setbacks — An 8-10°F night setback that works in Denver creates a humidity spike in Miami that takes hours to recover from
- Away mode too high — Setting to 85°F while at work allows humidity to climb above 65%, creating conditions for mold in just 24 hours
The fix isn't complicated — it's just different from what the manual says.
| Feature | Ecobee Premium | Google Nest Learning | Honeywell T9 | Honeywell T6 Pro |
|---|---|---|---|---|
| Price | $250 | $250 | $200 | $120 |
| Remote Sensors | 1 included | Sold separately ($40) | 1 included | None |
| Humidity Control | Good | Basic | Best | Good |
| Dehumidify Mode | AC overcool | Fan timer only | Dedicated mode | AC overcool |
| C-Wire Required | Yes (adapter included) | No | Yes | Yes |
| Geofencing | Yes | Yes (excellent) | Yes | No |
| Voice Assistant | Alexa built-in | Google built-in | Both via app | Both via app |
| Best For | Large homes with hot spots | Tech-savvy, set-and-forget | Humidity priority homes | Budget, straightforward |
Best overall: Honeywell T9 — best humidity control, remote sensors included, no-nonsense interface.
Best for tech enthusiasts: Google Nest Learning — excellent geofencing and learning algorithms, but humidity management requires manual configuration.
Best for large homes: Ecobee Premium — remote sensors detect hot spots and redirect cooling where needed.
- Turn off power at the breaker (not just the thermostat)
- Photograph your current wiring before disconnecting anything
- Label each wire with the terminal it's connected to (R, W, Y, G, C, etc.)
- Check for a C-wire — it provides constant 24V power to the thermostat
Most South Florida homes built before 1995 lack a C-wire (common wire). Your options:
- Included free with every Ecobee thermostat
- Installs at the air handler, no new wire needed
- Works with most single-stage and two-stage systems
- Not compatible with: heat pumps with auxiliary heat strips using W2
- Converts your existing 4-wire cable to carry a C-wire signal
- Brand: Fast-Stat Common Maker or Venstar Add-a-Wire
- Installs in 15 minutes at the air handler
- Works with Nest, Honeywell, and most other brands
- Google Nest can power itself from the G (fan) wire
- Trade-off: fan always runs with cooling (no independent fan mode)
- Acceptable in South Florida where independent fan mode increases humidity anyway
- Required for complex systems (multi-stage, heat pump with aux)
- 18/5 or 18/8 thermostat wire through attic or wall
- Cost: $150–$300 professional installation
- Worth it if you're also replacing the thermostat during an AC upgrade
Standard residential HVAC wire colors:
| Wire Color | Terminal | Function |
|---|---|---|
| Red | R (Rh/Rc) | 24V power |
| White | W | Heat (or W1/W2 for stages) |
| Yellow | Y | Cooling (compressor) |
| Green | G | Fan |
| Blue | C | Common (24V return) |
| Orange | O/B | Heat pump reversing valve |
| Brown | varies | Auxiliary/emergency heat |
Warning: Wire colors are conventions, not standards. Always verify by tracing each wire to the air handler control board. The terminal letter matters, not the color.
These settings are the core of this guide. Apply them after installation.
| Setting | Factory Default | South Florida Setting |
|---|---|---|
| Target humidity | 55–60% | 45–50% |
| Humidity alert | Off or 65% | 55% |
| Overcool to dehumidify | Off | On, max 2°F |
| Fan after cooling | Off | Off (running fan re-evaporates moisture) |
| Fan schedule | Circulate 15 min/hr | Off (adds humidity in shoulder seasons) |
Why "Fan: Circulate" is bad in South Florida: In dry climates, circulating air helps distribute temperatures. In South Florida, running the fan without cooling blows humid air across the wet evaporator coil, re-evaporating condensed moisture back into your home. This can add 5-10% RH.
| Time Block | Recommended Setpoint | Notes |
|---|---|---|
| Morning (6-8 AM) | 75°F | Comfortable wake-up |
| Day/Away (8 AM-4 PM) | 78°F | Max 78° to prevent humidity spike |
| Pre-cool (4-5 PM) | 75°F | Cool before peak demand pricing |
| Evening (5-10 PM) | 75°F | Active hours comfort |
| Sleep (10 PM-6 AM) | 76-77°F | Only 1-2° setback, not 8-10° |
Critical: Never set Away above 80°F in South Florida. National energy guides recommend 85°F for away mode. In South Florida humidity, 85°F allows indoor RH to climb above 60% within 2 hours. Above 60% RH, mold begins growing on drywall, wood, and fabrics within 24-48 hours.
- Home radius: 2 miles (South Florida traffic means you could be "close" for 30+ minutes)
- Away delay: 30 minutes (prevents away trigger for quick errands)
- Away setpoint: 78°F (not 85°F — see humidity warning above)
- Pre-cooling lead time: 30 minutes before arrival
If your home has 2+ zones:
- Upstairs zone: Set 1-2°F cooler than downstairs (heat rises)
- Guest room zone: Never fully shut off — minimum 80°F to prevent musty odors
- Use remote sensors to measure actual occupancy temperatures, not just hallway reading
- Check that temperature differential isn't set too small (less than 1°F causes rapid cycling)
- Verify overcool-to-dehumidify isn't set above 3°F
- If outdoor temp is above 95°F, your AC may legitimately need to run continuously
- Check fan setting: Must be "Auto" not "On" or "Circulate"
- Check filter: A dirty filter reduces coil contact time, reducing dehumidification
- Check sizing: An oversized AC cools too quickly and shuts off before removing humidity (short cycling)
- Check ductwork: Leaky supply ducts in the attic pull humid outside air into the system
- Remote sensors override the thermostat's built-in sensor — check which sensor is active
- Direct sunlight on the thermostat adds 3-5°F ghost reading
- Mounting on an exterior wall transfers heat through the drywall
- Ensure thermostat is within router range (interior walls reduce signal)
- Metal ductwork near the thermostat can block Wi-Fi
- Use 2.4 GHz network (better range than 5 GHz)
Realistic savings for South Florida, not manufacturer marketing numbers:
| Scenario | Expected Annual Savings |
|---|---|
| Replacing a manual thermostat with programmed schedule | $150–$300 |
| Adding geofencing (irregular schedule household) | $100–$200 |
| Optimizing humidity settings (reducing overcooling) | $50–$100 |
| Remote sensors (reducing hot-spot overcooling) | $50–$150 |
| Total realistic savings | $200–$500/year |
Savings assume a typical 2,000 sq ft South Florida home with a 3-ton AC system and current FPL rates.
docs/ecobee-humidity-settings.md— Step-by-step Ecobee humidity configurationdocs/nest-schedule-optimizer.md— Optimal Nest schedules for South Floridadocs/honeywell-t9-dehumidify.md— Honeywell T9 dehumidification setupdocs/wiring-diagrams.md— Common thermostat wiring configurations for South FL homes
Found something inaccurate or have a tip for a specific thermostat model? Open an issue or PR. We especially value feedback from South Florida HVAC technicians and homeowners with real-world experience.
MIT License — see LICENSE for details.
This guide is maintained by AC Repair Today — your licensed South Florida HVAC contractor. For professional thermostat installation including C-wire solutions, call (800) 917-2580.