Bathroom Fans Venting Into the Attic: Why It Matters

The fan turns on. The noise is there. But where is the air going?

A bathroom exhaust fan has one job: get the steam from your shower out of the house. Pretty often, I go up into the attic and find the fan's duct ends right there in the insulation, or it's fallen off, or it was never connected at all. The fan is working hard to move wet air from your bathroom into your attic.

Why that's a problem

• Moisture in the attic. Warm, wet air hits cooler roof decking and condenses, especially in winter.
• Mold and mildew on the roof decking and framing over time.
• Wet, matted insulation that doesn't insulate as well.
• Rot and rusted nails in the roof deck if it goes on for years.

Our humid East Texas climate makes it worse, because the attic air already holds plenty of moisture.

What I check

• That the fan runs and actually pulls air
• Where the duct goes, and whether it ends outside
• Whether the duct is disconnected, crushed or kinked
• Signs of moisture, staining or mildew on the decking near the fan

Is it a big deal?

Usually it's an easy fix: a qualified contractor runs the duct to a proper roof or wall vent cap. It's the kind of item worth fixing soon, before it turns into a moldy roof deck. If I do see staining or mildew around it, I'll show you and recommend the right professional to look further.

A quick tip for owners

Run the bathroom fan during your shower and for 15 to 20 minutes after. A fan on a timer switch makes that easy.