Insulate and air seal.

Your AC can provide either optimal efficiency or optimal dehumidification, but it can’t usually provide both. Air conditioners, designed for energy-efficiency, may not run cold enough to condense sufficient water vapor out of the indoor air. The air conditioner may fail to dehumidify a building for these reasons.

  • The air conditioner is oversized and doesn’t run long enough.
  • Thermostats control air conditioners by temperature, not Rh so if the temperature is satisfied, no dehumidification.
  • Fish tanks, plants, cooking, and showering create too much humidity for the AC to remove.
  • Energy-efficient AC evaporator runs too warm, or the airflow is too high, or both.
  • Humid air leaks through the building enclosure, introducing too much water vapor for the AC to condense.
  • Mild outdoor temperature during spring, fall, and at night doesn’t activate the AC thermostat.
  • Air sealing, insulation, exemplary windows, and shading combine to make indoor temperature and sensible-cooling load too low to activate the AC during humid weather.

Try these potential solutions.

Install a Dry Well

  • Do whatever possible to improve drainage and fix water leaks.
  • Pay for air-leakage testing, air sealing, and insulation when possible.
  • Ask your HVAC professional to adjust air-conditioner controls to run longer with a colder evaporator coil.
  • Consider a dehumidifier if you live in a humid climate and your indoor relative humidity reaches 60% or more.

A guide to low-cost cooling

For more information on low-cost cooling see Cool Buildings for Hot Weather

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