Moisture, mold & pests

High humidity indoors year-round

Consistently sticky or damp-feeling air inside the house makes mold, dust mites, and musty smells more likely, and usually comes down to too much moisture source and too little ventilation.

Difficulty
Easy
Time
1–2 hours to assess
DIY cost
$100–$300
Pro cost
$1000–$2500 for a whole-house unit

Symptoms

  • Air feels sticky or damp indoors even with AC or heat running
  • Condensation on windows or cold surfaces
  • Musty smell or visible mold in various spots

Likely causes

  • CommonInsufficient bathroom and kitchen exhaust ventilationDaily activities like cooking and showering add a lot of moisture that needs somewhere to go.
  • CommonOversized or poorly set air conditioning not removing enough humidityAn AC that cools quickly without running long enough doesn't dehumidify the air as effectively.
  • PossibleMoisture intrusion from a damp basement or crawl spaceGround moisture entering the lowest level can raise humidity throughout the house.

What to do

  1. Measure indoor humidity with a hygrometer in a few rooms; above roughly 50–55% consistently is a sign of a problem.
  2. Run bathroom and kitchen exhaust fans during and after activities that generate moisture.
  3. Check that exhaust fans vent all the way outside, not into the attic or crawl space.
  4. Address any known basement or crawl space moisture source, since it affects the whole house's air.
  5. Consider a whole-house dehumidifier connected to the HVAC system, or portable units in problem areas, if humidity stays high.
  6. Have an HVAC technician check that your air conditioner is properly sized, since an oversized unit cools without adequately dehumidifying.
  7. Recheck humidity levels after making changes and adjust as needed across seasons.

Tools and parts

  • Hygrometer
Whole-house or portable dehumidifierSearch: “whole house dehumidifier”

When to call a pro

Call an HVAC technician to evaluate air conditioner sizing or install a whole-house dehumidifier.

Safety

Generally low risk

Generally low risk for a careful person. Stop if anything looks different from what this guide describes.

Related guides

Operator provides AI-generated troubleshooting information. It can be wrong. For safety-critical, electrical, gas, structural, medical, automotive safety, or other high-risk problems, consult a qualified professional.