With the hot and humid summers that we experience in Southern Illinois, air conditioning is an important part of indoor comfort. High humidity also affects how the AC works. It is important to understand why high humidity impacts your HVAC system and what the options are for dealing with it.

Why Does Your House Feel Humid with the AC On?

Moist air holds more heat energy than dry air, which makes it harder to cool. As your body tries to cool you down by letting heat dissipate and sweat evaporate, it simply takes longer in moist air to cool off. Notably, the feeling can be significant. This is why the weather forecast includes the heat index, and a meteorologist talks about what it feels like compared to the actual temperature. To provide comfort, the AC must bring the heat index closer to your thermostat's target temperature.

Optimal Comfort Levels

Optimal humidity in a home is below 50%. Some people like their indoor air on the drier side, but be aware that relative humidity less than 35% can be uncomfortable and cause damage to things like flooring, wallpaper, and paint. If you experience sinus irritation in a very dry house with the air conditioning on, you might want to raise the humidity level to see if the discomfort goes away.

Dehumidification

Even when your air conditioner is running, it needs to remove excess humidity before your home truly feels cool and comfortable. Many AC units are unable to control indoor humidity when moisture levels are very high. Many homeowners add dehumidifiers to their homes to address this issue. With a dedicated whole-house dehumidifier, your air conditioning equipment doesn't have to work as hard to achieve your desired temperature.

Air Conditioner Sizing Issues

Notably, an air conditioner can be either undersized or oversized, and both conditions can impact indoor humidity and comfort. AC unit capacity is typically measured in tons or BTUs. As a general estimate, a 1,000-square-foot home may require around 1.5 to 2 tons (18,000–24,000 BTUs) of cooling capacity. Larger homes in humid areas like Southern Illinois might need 4 to 5 tons (48,000–60,000 BTUs), depending on insulation, layout, and local climate factors. An undersized AC will run constantly, struggling to cool your home or remove enough moisture from the air. Over time, that excessive strain leads to wear and tear, poor dehumidification, and higher energy bills. If your system seems to be running nonstop and never catches up, it may not be sized appropriately for your home. On the other hand, an oversized AC unit can also cause problems, particularly with humidity control. These systems cool the air too quickly and shut off before completing a full dehumidification cycle, which can leave the indoor air feeling cool but clammy. Short cycling also wastes energy and puts stress on components. If you're unsure whether your current AC is sized correctly, our technicians at One Hour Heating & Air Conditioning® can evaluate your system and perform a proper load calculation. Getting the sizing right is one of the most important steps to achieving consistent comfort, efficiency, and humidity control in your home.

System Age, Wear, and Tear

If you've noticed that your house feels more humid than it usually does, your system may be suffering from the effects of age, wear, and tear. Notably, the solution could be as simple as a tune-up. AC units can easily lose 5% of their effectiveness annually without a tune-up. Our technicians may be able to tweak a few settings, lubricate moving parts, recharge the refrigerant, and clean the coils to get your AC back to normal operation. Components do eventually fail. This doesn't necessarily mean that you need to replace your whole AC system, though. For example, the AC unit's compressor may fail after years of use. Many times, the compressor's performance declines rather than the whole unit failing. One of the first symptoms of a declining compressor is a noticeable increase in indoor humidity. The compressor struggles to power the unit, and then the unit doesn't pull as much moisture from the air. It is also a good idea to check out the condition of sensors and controls. A house might already have a dehumidifier, but perhaps the humidistat is getting old. Replacing or tuning the humidistat may be all it takes to restore normal comfort levels in the house. Thermostats can have similar issues, too.

Humidity and Mold

High humidity levels also drive mold growth in homes. This creates indoor air quality problems that can interfere with health and even hurt your HVAC's operation. The target level of preventing mold growth is 50% or lower. Mold growth is another indicator that your home might need a more aggressive dehumidification solution. If you smell musty odors from your AC's vents, then there's a good chance the humidity level in your home is too high. You may also see dust settling on the surface inside your home or experience an increase in allergies. Mold growth can clog the filter in your HVAC system. This is particularly true because humid air holds on to particulate matter more easily than dry air, leading to a greater contaminant exposure. This can also cause dust to settle on interior AC components, particularly coils, leading to system strain and potential damage. Options for addressing the problem are largely the same. You can add a whole-house dehumidifier to your HVAC system. Likewise, you will want to be sure that your AC is correctly sized for your home's demands. Additionally, you may want to look at replacing filters more frequently and cleaning the AC's coils to maximize performance.

Do You Need a Dehumidifier, or Can the AC Remove Humidity on Its Own?

If your house feels muggy in the summer despite having an appropriately sized AC unit, there's a good chance you'll need to consider a whole-house dehumidifier. Some locations have very high humidity levels. A house in a river valley might see higher humidity overnight and in the morning due to local conditions, for example. Conversely, there isn't anything wrong with primarily using just your AC unit if it's handling the job of dehumidification on its own. You may want to look at a whole-house dehumidifier to handle days that are very humid but slightly warm, especially during the summer months. This is a good way to get relief without straining your AC, which can lead to frequent repairs and shortened system lifespan. One Hour Heating & Air Conditioning® offers a 100% guarantee of satisfaction with all our work. People have trusted our brand since 2003. We take pride in handling heating and cooling work for customers in Herrin, IL, and the surrounding areas. Customers can schedule assistance with installations, repairs, replacements, and maintenance. Our technicians are experienced and reliable, and they provide straightforward pricing for all projects. We offer 24/7 availability. We are always on time … or you don't pay a dime! Our team brings great integrity and honesty to each job, and you can relax knowing we'll respect you and your property. If you're worried about humidity issues in your Herrin home, contact One Hour Heating & Air Conditioning® today.