Humidity · Guide
AC and Humidity Settings for an Empty 30A Second Home
Insured Florida LLC · Watersound Origins · Alys · Rosemary · Scenic 30A
The air on 30A is the thing most likely to damage a house that sits empty. Mold, swollen doors and a musty smell almost always trace back to a thermostat setting or an AC that quietly stopped pulling water out of the air.
By Ryder Schilling, owner of Coastal Home Management 30A · Updated September 27, 2026
The short answer
An empty second home on Scenic 30A should keep the air conditioning running, set around 78 to 80°F, with indoor humidity held below 60 percent and ideally near 50. Turning the AC off, or letting an eco or away mode float the house past about 82°F, lets Gulf Coast humidity build fast enough to grow mold within days. The most common failure in a closed-up 30A house is a clogged AC condensate line, which shuts the system off or leaks into the ceiling. Coastal Home Management 30A checks the thermostat, humidity reading and condensate line on every home watch visit.
The settings
The Environmental Protection Agency recommends keeping indoor relative humidity below 60 percent, ideally between 30 and 50. On 30A the outdoor air sits well above that most of the year, so the AC is doing two jobs: cooling and pulling water out.
| Setting | Empty 30A home | Why |
|---|---|---|
| AC | On, cool mode | Off means no dehumidifying at all |
| Temperature | 78 to 80°F | Warm enough to save money, cool enough to keep running |
| Humidity | Under 60%, aim for 50% | Mold needs sustained humidity above about 60% |
| Fan | Auto, not On | On blows water back off the coil into the house |
| Eco or away mode | Off, or capped at 80°F | Some float the house to 85°F or more |
| Ceiling fans | Off | They cool people, not rooms |
Why cooler is not always drier
An AC only removes moisture while it runs. A system that is oversized for the house cools the air in short bursts and shuts off before it pulls much water out, so the house feels cold and clammy. If your thermostat reads 76°F but humidity sits at 65 percent, a lower temperature will not fix it.
Thermostats with a dehumidify setting, or a whole-home dehumidifier on the return, solve that. A smart thermostat that shows humidity lets you watch it from wherever you are.
The part that fails most: the condensate line
Every AC drips water from the coil into a drain line. On the coast that line grows algae and clogs. When it does, a float switch shuts the whole system off, or, on older units, the pan overflows into a ceiling or closet. Either way the house starts climbing in heat and humidity, and nobody knows until someone walks in.
This is the single most common thing a home watch visit catches in a closed-up 30A house. It is also why a humidity number from a smart thermostat is not enough on its own: the thermostat can keep reporting while the unit sits tripped.
Before you leave
- Set 78 to 80°F, fan on Auto, and turn off any away mode that lets it float higher
- Put in a new HVAC filter
- Leave interior doors open so air moves through every room
- Crack the cabinet doors under sinks and leave closet doors open
- Close the blinds on the sun side of the house
- Have the condensate line flushed once or twice a year
- Give your home watch company the thermostat app login or show them the humidity reading
Have someone read the thermostat for you.
Weekly and every-other-week visits, with photos and a written report every time. The first home check is free.
Questions
Asked plainly.
Should I turn off the AC in my 30A second home when I leave?
No. On the Gulf Coast the AC is what keeps humidity down. A house left with the AC off can reach mold-friendly humidity within a few days in summer.
What humidity is too high in an empty house?
Anything that stays above 60 percent for more than a day or two. Aim for about 50 percent. A hygrometer costs a few dollars and many smart thermostats show humidity directly.
Do I need a dehumidifier on 30A?
Not always. A correctly sized AC set to 78 to 80°F keeps most homes under 60 percent. If yours reads higher with the AC working, a whole-home dehumidifier on the return, installed by a licensed HVAC contractor, is the fix.
How often should someone check an empty house for AC problems?
In summer, weekly is the safe interval, because a tripped AC can raise humidity to mold levels in under a week. Every other week works for many homes in the cooler months.
What does a home watch visit check on the AC?
On every Coastal Home Management 30A visit: the thermostat setting and indoor temperature, the humidity reading, whether the system is actually cooling, the condensate line and float switch, and any water around the air handler. HVAC filter changes are included on Coastal Elite.