We all know what humidity does to Aunt Linda’s hair, but do you know what humidity does to your air conditioning system? Understanding humidity, its effects on your air conditioner, and how to control humidity levels in the home will help you increase your comfort during the dog days of summer.

What Is Humidity?

High indoor humidity can negatively affect the efficiency and longevity of your A/C and cause health problems for you and your family. But what is humidity, anyways? There are two main measures of humidity:

  • Absolute humidity measures how much water vapor is in the air, regardless of the temperature. To calculate the absolute humidity of a given volume of air, the mass of water vapor is divided by the mass of dry air.
  • Relative humidity measures the actual amount of water vapor in the air compared to the highest possible amount of water vapor that could be in the air at that temperature. Warm air can hold more moisture than cool air.

High humidity makes the air feel muggy, stuffy, oppressive, and steamy, among other unpleasant feelings.

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How high humidity affects us

Our bodies sweat to regulate our temperature. The body perspires, releasing water and salt, and when this water evaporates it takes some of the body’s heat with it. If the relative humidity is high, sweat evaporates slowly because the air is already saturated with moisture and does not have the capacity for more. There’s nowhere for your sweat to go.

This is why you feel so hot on humid days, even if the temperature is at a normally tolerable level. Your body has a harder time regulating its temperature, which means it becomes more susceptible to heat stroke. Take extra precautions when you go out in the heat and humidity.

Many of us stay indoors during swelteringly humid days, but sometimes there’s no escape from the humidity, not even in your air conditioned home.

Air Conditioning and Indoor Humidity

condensation on window from high humidity levels

What is the ideal indoor humidity level?

The ideal indoor humidity level is between 30 and 50–60 percent. You can determine whether you have high humidity levels in your home by:

  1. Testing your indoor humidity levels with a hygrometer, which can be found at most home improvement stores.
  2. Checking your windows for condensation and your walls and ceilings for moisture or mold.

Indoor humidity can get too high if the outdoor humidity levels are high and outside air gets into your home, such as through opened windows or poor seals around your windows or doors. Indoor humidity levels can also be affected by activities that increases moisture, such as cooking, showering, or hanging clothes to dry inside.

Does air conditioning control humidity?

Your air conditioner is controlled by the thermostat, which senses temperature—not humidity. When the temperature climbs above a certain level, the thermostat tells the air conditioning to kick on.

While your air conditioning is working, some moisture is drawn out of the air. However, air conditioners are not specifically designed to control humidity, so they can’t always handle the amount of water vapor in the air.

Turning the thermostat temperature down won’t increase your A/C’s ability to remove humidity from the air.

What happens to my A/C when it’s too humid inside?

If your home is too humid, the air conditioner will have to work overtime to make you comfortable. You’ll likely be tempted to turn the thermostat down further than you normally would to get relief from the oppressive humidity. But an overworked air conditioner will run less efficiently and require more maintenance. The lifespan of the unit will decrease as energy bills increase.

How does humidity affect mold growth?

Humidity levels above 50 percent encourage mold and mildew growth. Whether mold is growing on your walls, your bathroom ceiling, or inside your air conditioner, the system can circulate mold spores throughout your home. Mold can cause or irritate health issues and can grow on furniture, clothes, and food, so it’s in your best interest to solve your high indoor humidity problem.

How to Control Home Humidity Level

HVAC technician repairs air conditioner unit

Regular maintenance checks

This is probably the best thing you can do for your air conditioning and heating system, period.

Regular maintenance of your system allows your HVAC pro to catch issues before they become catastrophic. Your A/C technician will also monitor the health of your equipment and keep the system clean. Consider signing up for an HVAC maintenance program in order to proactively care for your system.


If you need to dehumidify your space, a dehumidifier is a logical choice. There are stand-alone options as well as whole home dehumidifiers that are installed into your existing HVAC system.

Dehumidifiers use the process of condensation to remove moisture from the air.

  • Air enters the system and passes over cooling coils.
  • The temperature of the air drops, and so does the air’s capacity to hold water vapor.
  • The water vapor condenses into liquid and collects in the dehumidifier’s reservoir.
  • The system then reheats the air and puts it back into the room.

Ask your HVAC pro if you’re not sure what type of dehumidifier is best for your situation. If you’re not ready to install a whole home dehumidifier, there are plenty of stand-alone options available, although you may need to purchase more than one to address humidity in multiple rooms.

New air conditioning system

If you’re having a lot of problems with your air conditioning and it’s time to replace it, this could be an opportunity to get a new A/C with a higher SEER rating than your current unit. Ask your air conditioning technician about installing a whole home dehumidification system at the same time as your new air conditioner.

The Bottom Line

  • Ideal indoor humidity is generally between 30 to 50 percent relative humidity. Anything higher than 50 percent is a recipe for mold growth.
  • Humidity is hard on your home. Take control by measuring home humidity levels and implementing solutions if levels are too high.
  • Take care of your air conditioning system. Schedule regular HVAC maintenance to ensure your system runs efficiently throughout the year.

Contact a professional HVAC company today to schedule an inspection of your air conditioning system.