Leaving a Florida House Empty for the Summer

Half the homes we inspect in the fall have the same story attached. The owners left in May, came back in October, opened the door, and immediately knew something was wrong. Nothing dramatic happened while they were gone. That is precisely the problem.

The number that matters is not temperature

The standard advice is to set the thermostat to 80 and leave. It sounds sensible and it is the single most reliable way to come home to mold.

Here is why. Your air conditioner removes humidity only while it is actually running. Set to 80 in an empty house with the blinds drawn and nobody cooking or showering, the system barely reaches that setpoint, so it barely runs. Barely running means barely dehumidifying. The house stays at 80 degrees and climbs to 70 percent relative humidity, and at that level surfaces stay damp enough for growth without one drop of water entering the building.

Temperature is the thing you can feel and humidity is the thing that does the damage. An empty house does not care whether it is comfortable.

What to actually set

Aim to hold relative humidity below about 60 percent, and ideally in the 45 to 55 range. There are a few ways to get there.

A thermostat with a built-in humidity setpoint is the cleanest option. Set the humidity target and let it call for cooling to hit that number rather than a temperature. Many modern units do this and most people never turn the feature on.

A separate humidistat wired to the system does the same job on older equipment and is a modest install.

If you have neither, setting temperature lower than you want to, around 76 to 78, is the crude version. It costs more in electricity than 80 and much less than remediation. This is the tradeoff people get wrong: the summer of AC bills is a fraction of what opening walls costs.

Whatever you choose, a cheap wifi hygrometer that reports to your phone turns this from a hope into a fact you can check from a thousand miles away.

Before you leave

Shut off the water supply to the house at the main. This is the highest-value thing on the list and it takes a minute. An unattended supply line failure is the single most destructive thing that happens to a closed-up house, and there is nobody there to notice for months.

Change the air filter, because a loaded filter restricts airflow and hurts dehumidification exactly when you need it most. Clear the condensate line and pour a little vinegar through it, since a clogged line in an unoccupied house either shuts the system down or overflows into the closet.

Open interior doors and closet doors. Air movement is free and stagnant pockets against exterior walls are where growth starts. Leave the fan set to auto rather than on, because continuous fan can re-evaporate moisture off the coil back into the house.

Pull anything organic out of the pantry and take the trash. Photograph the house on the way out, which costs nothing and is useful if anything does go wrong.

Have somebody actually walk through

Remote sensors tell you the humidity. They do not tell you that a ceiling has stained or that the closet smells. Ask a neighbor, a friend, or a property manager to walk the house every few weeks, look at ceilings and under sinks, and confirm the air handler is running and the closet floor is dry.

A leak found in week two is a repair. The same leak found in month five is a renovation.

When you come back

Do the first-breath test. Walk in and pay attention before your nose adapts, which takes only a few minutes. A musty first impression is real information and it is the most sensitive instrument you own.

Then look at ceilings below roof valleys and around penetrations, the exterior-wall side of closets, the base of walls behind furniture, under every sink, and inside the air handler closet. Check the drain pan.

If it smells and you cannot see anything, that is normal and it does not mean you are imagining it. Odor moves through cavities and ducts and shows up rooms away from its source.

The seasonal pattern we see

This is not a rare failure. It is the most predictable thing in our calendar. Homes across the 55-plus and snowbird communities from Boynton to Jensen Beach sit closed from May through October, through the entire wet season, on a thermostat setting chosen to save money. We find the same growth in the same places year after year: primary bedroom exterior walls, master closets, and the underside of ceiling drywall in the coolest rooms.

It is also almost entirely preventable, which is why it is worth a page rather than a shrug. Control the humidity, kill the water supply, and have someone look at the place.

If you are back and something smells off, call (561) 632-6387. We inspect and test only, so if the house is fine we will tell you it is fine and you can stop worrying about it.