By Hood Service Company · Corsicana, TX · Updated
The short version
- Aim for indoor relative humidity roughly between 30 and 50 percent, and keep it below 60 percent.
- Your air conditioner removes moisture as it cools, but only when it runs steady, full-length cycles.
- An oversized AC or a fan left set to 'On' can leave a home cool but clammy.
- A whole-home dehumidifier may help when a correctly working AC still can't keep up.
What is relative humidity, and what level should you aim for?
Relative humidity is how much moisture the air holds compared with the most it could hold at that temperature. The U.S. EPA recommends keeping it below 60 percent indoors, ideally between 30 and 50 percent.
Because cooler air holds less moisture, the same amount of water vapor reads as a higher percentage as air cools. That's why a cool house can still feel damp. A digital hygrometer placed away from the kitchen and bathrooms gives you a reading to compare against that range.
Why do Texas homes get so humid?
North-Central Texas sees humid springs and early summers, and moist outdoor air finds its way inside through leaks, open doors and ventilation. Cooking, showers, laundry and the people living there add more moisture every day.
- Outdoor air leaking in around doors, windows, attic hatches and leaky ducts in unconditioned spaces.
- Daily living: showers without the bath fan running, cooking without the range hood, and drying clothes indoors.
- Mild, muggy days when it isn't hot enough for the AC to run much, so it removes little moisture.
- Damp spots such as standing water near the foundation or a crawlspace that stays wet.
How does your air conditioner control humidity?
As warm air passes over the cold indoor coil, moisture condenses on the coil and drains away. That works well only when the system runs steady cycles long enough to wring water out of the air.
An oversized system cools the house quickly and shuts off before it removes much moisture, leaving the air cool but clammy. Systems with a two-stage or variable-speed compressor can run longer at lower output, which often helps with moisture removal. Sizing is covered in HVAC sizing and load calculations.
Your thermostat's fan setting matters too. With the fan set to 'On,' the blower keeps running after cooling stops and can blow moisture from the wet coil back into the house. 'Auto' is usually the better summer setting for humidity.
What are the signs your home is too humid or too dry?
Too much moisture shows up as a clammy feel, musty odors, foggy windows and condensation on cool surfaces. Air that's too dry, more common on cold winter days with the heat running, brings static shocks and shrinking wood.
Sustained high humidity can encourage mold growth and damage finishes and furnishings, so it's worth fixing the cause rather than just turning the thermostat lower.
- Too humid: sticky air even at a cool setting, musty smells, condensation on windows or supply vents, mildew spots in closets or bathrooms, and doors that swell and stick.
- Too dry: frequent static shocks, gaps opening in wood floors or trim, and hygrometer readings that stay below about 30 percent.
What can you do to bring humidity under control?
Start with simple habits and settings, then have the system checked. If the AC is sized and working correctly but the house still feels damp, a whole-home dehumidifier or other indoor air quality equipment may help.
A whole-home dehumidifier works with your ductwork to remove moisture independently of cooling, which helps on mild, muggy days. If your AC runs and runs without the house ever feeling dry, our HVAC troubleshooter can help narrow down why. Our indoor air quality services page covers the options, and you can contact us to talk through what your house needs.
- Set the thermostat fan to 'Auto' during cooling season.
- Run bath fans during and after showers, and the range hood while cooking.
- Keep the air filter clean so the system moves its full airflow. See air filters and MERV ratings.
- Take a quick look around the indoor unit and condensate drain line. If water is pooling or the drain pan is full, call a technician.
When should you call a technician?
- Indoor humidity stays above 60 percent even with the AC running normally.
- Water is pooling around the indoor unit, or the drain pan or condensate line is backing up.
- Supply vents or ducts are sweating or dripping.
- Your AC runs short on-off cycles and the house never feels dry.
- You keep finding mildew or musty odors you can't trace to a source.
Frequently asked questions
Should I buy a portable dehumidifier or a whole-home unit?
A portable unit can help a single room or a damp area, but it needs emptying or a drain and covers limited space. A whole-home dehumidifier ties into the duct system and handles the entire house. The right choice depends on how widespread the problem is.
Will lowering the thermostat reduce humidity?
Sometimes a little, because the AC runs longer. But if the system is oversized or the fan is set to 'On,' a lower setting may simply make the house colder and clammier. Fixing the cause works better than chasing a lower number.
Can my home be too dry in a Texas winter?
Yes. During cold stretches when the heat runs often, indoor humidity can drop. If readings stay low and you notice static and shrinking wood, ask a technician whether humidification makes sense for your home.
Does a new AC automatically fix humidity?
Not automatically. Correct sizing, airflow setup and sealed ducts matter as much as the equipment itself. A load calculation and a look at the ductwork help make sure a new system controls moisture well.