Bathrooms equal moisture, and the more people living in your home the more moisture there will be– especially if you have teenagers. Every bathroom needs a fan to exhaust the hot, moist (and sometimes odorous) air from inside your home to the outdoors. This will prevent moisture and mold from damaging your bathroom structure. Even if you have a window, without an exhaust fan, humidity in your bathroom can cause brown water stains on the walls, peeling paint, and swollen drywall. Wouldn’t you rather install a fan and some simple ductwork than redo your entire bathroom?
The most common mistake people make when installing a bathroom fan is to do just that and nothing more. Without a ventilation system, your bathroom fan dumps all that hot, moist air into your attic or between the walls, subjecting your roof, insulation, ceilings, and your entire home to the moisture damage that once threatened your bathroom. Over time this will create the perfect environment for mold and bacteria to grow and spread throughout your home. Your roof in particular is at great risk to heat and moisture damage. When your attic is full of hot humid air, the roof sheathing will warp and the shingles will deteriorate, shortening your roof’s lifespan and causing you to replace it sooner.
To ensure your bathroom and the rest of your home is adequately protected from moisture damage, your bathroom fan will need to be equipped with a 4” duct pipe from the fan to a stem vent and both ends foil tape sealed to the outdoors.
To assemble a proper ventilation system, you’re going to need:
4” vent duct piping (smooth rigid) and 2 swivel elbows
bubble wrap insulation for around the duct if it’s longer than 10 feet
2” foil HVAC tape
4” metal stem vent which means it has a 4” nipple to receive the exhaust duct
and obviously the bath fan (with 4” outlet) installed in the ceiling and wired
Exit Strategy and Duct Orientation
Before you purchase the materials you need, it’s important to decide on the best duct and vent orientation for your situation. You have options:
You can direct the air to a soffit vent, but this is a poor choice if you have existing attic intake vents at the soffits. The bathroom air that is pushed out through the soffit could be pulled right back into your attic at the intake vent and defeat your efforts.
You can also direct the air to a gable vent if there is one close by. Running long ductwork to a distant gable vent could allow condensation to build on the inside of the duct as the hot air spends too long in the piping. You really want to use the shortest distance possible from the fan to any outside access point.
In most cases, the best exit strategy is to ventilate bathroom air through the roof. To do this, you’ll need to cut a very precise hole in your roof, which is an intimidating task for many homeowners– and for good reason. There are plenty of ways cutting a hole in your roof can go horribly wrong. So when in doubt, don’t hesitate to call a professional roofer.
This video from GAF offers a helpful step by step guide to installing your ducts and roof vent.
Quick Tips For Installing Your Bathroom Exhaust System
Ninety degree angles in ductwork should be avoided to maintain easy airflow. Instead, use two 45 degree corner pieces to create your 90 degree angle.
Fan ports are usually 3” or 4” in diameter. To reduce pressure on the fan, select a duct pipe with a larger diameter and get an increasing component to connect it to the port. This will allow for maximum efficiency.
It is best to use rigid piping over plastic or aluminum flex hose material unless you have a very short run. The inner surface of flex hoses is rough, which can disrupt the flow of air.
Not every region’s building codes require duct insulation, but if you want to be absolutely sure that you’re safe from condensation and moisture damage, its a good idea to insulate your ductwork.
For detailed guidance with your bathroom exhaust system installation, contact Pacific West Roofing today. Call (503) 635-8706 or click here to use our contact form.