You turn on the bathroom fan and it "ventilates," drawing out humid and stale air, but to where? It pays to do a ventilation check before your fan wrecks your attic or crawl space. Here's why: While exhaust fans should always be vented outside your home, many homeowners unhappily discover that their bathroom fan vents directly into their attic or crawl space. And, whether by carelessness or shoddy workmanship, it has been delivering a steady supply of humid air and moisture onto raw wood, insulation and drywall surfaces, often for many years. This leads to the potential for wood rot, fungus, and mold to develop. To find out if your fan vents outdoors or not, climb into your attic or under your house to see if there's a flexible metal duct leading from each fan to an outside roof or wall vent. If there isn't, and there's evidence of moisture near the fan's exhaust outlet, take immediate steps to correct the mold and exhaust situation. And that's the On The House tip for today.