Moisture Captured; The Problem Born Of Energy Efficiency

Let’s face it inside our home has always been there, and always will be as long as we cook and bath in our houses. When houses were “loose” not insulated well and had an abundance of air changes a day indoor pollutants and interior levels were not a concern. As houses are constructed tighter and tighter and every void is now filled with insulation, indoor air quality and issues have risen to problem level. Something as simple as cooking pasta or making homemade soup can and does add a lot of moisture into a home environment.  A quick and simple kitchen solution is to always run your kitchen exhaust fan when you are cooking, and make sure it is vented to the outside and does not just recalculate the air.

We are going to focus this article on bathroom moisture and how to reduce it correctly. The greatest aid in removing moisture from the bathroom is the exhaust fan. If it is not used and sized correctly it will have less than the optimum effect.

One of the ratings on exhaust fans is , “cubic feet per minute” of air displacement. To properly size the fan to your bathroom lets me introduce you to a formula that is used to calculate the correct size of fan needed. Use this formula WxLxHx8ACH = CFH then divide by 60m to get . (Cubic feet per minute is width x length x height x 8 air changes an hour = cubic feet per hour /60 minutes to get cubic feet per minute). A shortcut method is if you have an 8’ ceiling measure the square footage of the floor, say a 9’ by 5’ bathroom floor would equal 45 sq ft and 45 . It is important to properly size the fan because a fan that is too large will waste energy running and also remove too much heated/cooled air from the room.

Remember fans are there to remove moisture and odors, and the closer they are to the source, the better they will function. If you are installing a fan in an enclosed toilet room then consider a vertical mount position on a wall next to the toilet. If you are going to do this then make sure your fan is approved for vertical installation and that the required exhaust duct will fit in the existing wall cavity. If you are installing in a combination bathroom, toilet and tub/shower in the same room then a ceiling mount is the standard method of installation.

When installing the fan in the ceiling do not place it to close to the tub or you could create a draft situation. The goal here is to capture the warm moist air as it is naturally displaced by the water from the shower and not create a vacuum where air is literally sucked out of the shower area. Remember any air traveling over wet skin will feel cool.  A point to remember is as air is removed from the room new air must flow into the room, typically from under a door or from other openings. The discussion of negative pressure situations is a discussion for another article. Experts agree that leaving the fan run for 20 minutes after the water is turned off is sufficient time to remove the excess moisture. Another gauge is when the steam is gone from the bathroom mirror.

If you are installing a new exhaust fan then install a separate switch to operate it, so that you can leave it on without leaving a light on. When venting your fan make sure you vent it to the outside, not just into attic space or you will just be moving the moisture problem from the bathroom to the attic where it can be as troublesome.

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