Bathroom and kitchen exhaust fans are good things. They remove moisture and odors right where they are created. But leave them running for hours, or install a fan that runs constantly, and in our climate they can quietly make the whole house more humid.
Air out means air in
A house is a closed box. When a fan pushes air out, the same amount of air has to come back in somewhere: around windows and doors, through the attic, through gaps around pipes and wires. On a summer day on the Northshore, that replacement air is hot and full of moisture.
If the replacement air comes through the attic or a crawlspace, it can also bring dust and odors with it.
Use them the right way
- Run bath fans during showers and for about 20 minutes after, then turn them off. A timer switch makes this automatic.
- Use the range hood every time you cook, and make sure it vents outside rather than recirculating.
- Avoid running a whole-house or attic fan in humid weather.
Fresh air, without the moisture
Homes still need fresh air. The answer is controlled ventilation: bringing in a measured amount of outdoor air through a known path, filtered, and paired with dehumidification so it does not raise indoor humidity. Monitoring CO₂, VOCs and humidity tells us how much fresh air your home actually needs.