how to extreme

Fan-tastic Bath Venting Tips

Bath, Construction How-To, Projects, Remodeling March 22, 2017 Sonia







Circulate fresh air and get rid of unwanted moisture.

By Rob Robillard

Prior to and even during a bathroom remodel, I often have conversations about tile and fixture layout, style and finish. But the conversation seldom leads to discussion of bathroom ventilation, issues like CFMs, minimizing ductwork and the placement of external heads and backdraft dampers.

In my Boston Globe column and on my ConcordCarpenter website, I often receive questions relative to ventilation and moisture in bathrooms. Unfortunately, there’s plenty of misinformation about bathroom ventilation.

Some folks ask if it’s okay to vent moist shower air into a roof soffit or unheated (but vented) attic. Others ask whether they should be concerned about their current “mile-long” plastic duct tubing.

Then there are those who complain of having a mystery stain on their ceiling. The stain is the result of a fan pipe that was installed through an unheated attic where moisture built up from a pipe dip, froze, and months later melted, staining the plaster ceiling below. Mystery stain solved!

Not venting a shower or improper venting can result in high humidity in the bathroom. When bathroom humidity builds up, warm moisture-laden air moves toward cooler wall surfaces, where it condenses back into water.

Moist air can also work its way into a wall cavity and condense inside the wall. Both situations can result in mold, odors and sometimes structural damage.

Moisture will also peel off wallpaper or paint. Seeing or smelling mold and mildew is a good indicator that you have a high moisture problem.

So how do we remodel our bathrooms and still enjoy that hot, steamy shower and avoid mold problems?

This loft ceiling will be home to the new bath fan on this project.

The only effective way to prevent mold is to attempt to keep indoor moisture levels low. A properly vented bathroom shower fan will remove moisture and decrease the humidity in your house.

Inspect the framing to determine the best duct path and mounting position for the fan.

Choosing the Best Exhaust Fan

The most important feature in a bathroom shower fan is its ability to remove moisture not only as it’s created but also while moisture droplets are floating in the air prior to condensing on the walls and ceilings.

Establish a wiring path for the power supply and switch control.

In order for a bathroom fan to do its job you need to focus on five main points:

  • Sizing the fan to the room
  • Placing the fan in the best location to succeed
  • Installing the fan properly
  • Mitigating fan noise
  • Timer switch

Sizing the Fan

Prior to purchasing your bathroom fan you’ll need to size it to your room so it can adequately handle the airflow for that space. That means you need to match the fan CFMs to the size of your bathroom. Most people size the fan to the room dimensions correctly but fail to factor into their calculations the length of duct run and elbows.