Humidity & AC

An air conditioner consumes energy at a rate that is determined by both the outdoor temperature and relative humidity.

You air conditioner reduces the air temperature and also reduces the relative humidity in your home. Removing moisture is important to comfort because high humidity slows the evaporation of sweat from your skin.

In an air conditioner, the refrigerant in the evaporator coil extracts heat from the moving air. But this cool coil surface also encourages condensation to take place, as moisture from the room air reaches its dew point. This condensation releases heat, which is removed by the air conditioner. Higher humidity leads to more condensation, and more condensation produces more heat for the air conditioner to remove. This increases your electricity costs.

If it seems odd that condensation releases heat, just think about getting out of the swimming pool and how the evaporation of water from your skin cools you off. Water condensation, on your evaporator coil or anywhere else, is just the opposite. Heat is released wherever water condenses.

You can reduce the cost of air conditioning by following these steps to reduce the humidity in your home:

  • Cover the ground in your crawl space with a ground-moisture barrier to reduce summer indoor relative humidity.
  • Be sure your dryer is vented to the outdoors
  • Avoid drying clothes on an indoor clothes line
  • Cover pots when cooking
  • Use exhaust fans in your bathroom and kitchen
  • If you don’t have exhaust fans in your bathroom and kitchen, have them installed
  • If you have a crawl space, be sure any bare dirt is covered with a plastic ground-moisture barrier

When you reduce the humidity in your home, you also reduce the possibility of having mold and mildew growth. There are a lot of a good reasons to control moisture in your home year round.

To avoid high indoor summer humidity, remove moisture where it is released: in the bathroom and kitchen.

See also Control Moisture in Your Crawl Space, How Moisture Moves Around in Your Home, Building Science: Moisture and Humidity , and Solving Moisture Problems.

Both Residential Energy: Cost Savings and Comfort for Existing Buildings and Saturn Energy Auditor Field Guide contain more information about solving moisture problems.