Bath Fan or no Bath Fan?

Bath fan or no bath fan?
Is it really important to have a bath fan?
Bathroom renovations are a big part of what we do at Home Remodeling Pros and it is no surprise that often times homeowners are misinformed about the importance and purpose of bath fans. While this post is not intended to provide a definitive answer to whether or not your specific bathroom needs a fan, we hope that this post will provide some useful information for anyone pondering the purpose or importance of our old friend the bath fan.

To start, while it is a nice added benefit at times, the bath fan’s main purpose is not really to expel odors. It’s main purpose is to remove humidity from the bathroom.
Why is it important to remove humidity from the bathroom?
Great question. The two answers are mold and rot. Let’s focus just on mold since it’s a far more common issue.
An esteemed professor of mine, Paul Fisette, taught me that mold spores are everywhere and they require the same three things that we require to stay alive: oxygen, food, and water. Since most residential building components constitute as food for mold and we humans would also have a hard time if we somehow removed oxygen from our homes, we then turn to controlling water. In Maryland, outdoor relative humidity levels tend to range between 20% and 40% in the colder months, and 50% to 75% in the warmer months. Building occupants inadvertently increase humidity levels slightly with the vaporization of sweat and running of cold water and we increase humidity levels greatly with the use of hot water for things like cooking, dishes, and showers. When it is cold and dry outside, this can be a good thing and we may feel more comfortable when we are increasing the humidity levels. When it is hot and humid outside, this can be quite problematic. One saving grace is that air conditioning also does a great deal of dehumidification. Mold has sufficient water to absorb from building materials when relative humidity levels are above roughly 70%, depending on temperature, for an extended period of time, which typically only occurs naturally for short periods of time but can be an issue in the bathroom where showers frequently take place and it’s a smaller enclosed space (do you shut doors to enclose your kitchen?). So how do we prevent mold growth in the bathroom? You could try not showering… or, alternatively, we could mitigate the time spent at or above 70% relative humidity so that mold spores are unable to thrive. How do we reduce the humidity?
Building code states that a bathroom must be equipped with ventilation to the exterior either by window or by a bath fan that terminates to the exterior of the building. The problem with this code is that few people actually open their bathroom windows. Luckily many of these homes have vents for heating and air conditioning in the bathroom forcing new air into the room which in turn forces the old air out and I’ve seen few homes that have actively used air conditioning vents in the bathroom with mold issues. It’s the homes where the humid air is allowed to remain stagnant in the bathroom where problems are most common. So, if you have a bathroom without an AC vent or bath fan and you don’t open the window frequently, you may be at risk for mold growth. Feel free to share your stories and how they compare with what we’ve shared in this post!

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