Where should you vent a bath fan?

Bath fans, or bathroom fans, are important pieces of equipment to remove moisture from your attic. Not long ago we watched a video online that was nicely edited - and the host spoke with confidence on how to vent the bathroom fan to the outside. In the first 30 seconds, he told us 3 wrong ways of doing it, thought he was convinced he was doing it right. Make sure you make the right choice for your home.

Why vent the bathroom fan to the outside? 

  • You want to remove moisture from your home. 
  • Taking hot showers can put a lot of moisture in your home. If the moisture is not removed properly from the home, you may have a mold problem on your hands. 

What happens if you do not vent the fan properly?

  • Strong likelihood of mold! Look below, the bath fan is vented to the soffit (not the way to do it)

The bath fan is located in the center cavity just below the eave chute. When a bathroom fan is vented into the soffit, it puts the moist are outside. Many contractors do this as it's easy and they do not have the proper knowledge. Then, due to how the attic ventilates, the moist air reenters the home right through the eave chute. As you can see on the other cavities, no mold / moisture problems!

What are the best practices of venting the bath fan to the outside, and why?

  • Vent to the outside - put the duct through the roof, air seal, install roof cap on the roof, and use tar to seal down shingles
  • Use rigid duct, not flex duct
  • Do not vent into the soffit nor in the attic
  • Use duct wrap insulation to insulate the ducting. This prevents chances of condensation in the winter

Dangers of Too Much Air Sealing

Every home has to breathe. Air has to enter and air has to leave. Otherwise, pollutants can stay in the home and affect your health. Moisture can build up and damage the home's structure and/or create mold. We are certain that you want to be healthy and have a solid home structure to have a good resale value. 

We talk so much about air sealing because it is so important to limit the amount of air changes occurring in a home. There are a lot of companies out there who will spray foam your wall cavities, attic spaces, basement spaces - or will even rent you the equipment to do it yourself to save a few bucks. The thing they do not do is actually test your home for air infiltration. Effectively they seal up your home, stop air from entering, but have no idea how much should be entering and much actually is entering. Sounds a little unsafe to me. 

Every home has a standard level of how many air changes it needs per hour called the Building Airflow Standard. This is easily calculated after finding the volume of your home. Next, you need a blower door test to confirm how leaky or tight your home is. You may seal up to 70% of the BAS levels before needing mechanical ventilation to bring more air into the home. 

At Sellair, we want to air seal properly. We want to make sure your home is left with proper ventilation so that you can feel confident knowing that your home is not only more comfortable and energy efficient, but that your home is also attaining the proper amount of ventilation because it was air sealed the correct amount. 

The right thing to do is to get an Energy Audit before air sealing your home. Then after air sealing is completed, run the blower door again to confirm your results. If you air seal too much, bring in mechanical ventilation to the home. This will give you adequate amounts of airflow and filter pollutants in the home. 

While this may be a lot of information, we are here to educate you. Please contact us if you have any questions or concerns regarding this process.