Installing a Bathroom Exhaust Fan

Ventilate space properly with a quiet and efficient fan.

Many homeowners take hot baths or showers without thinking about the impact of moisture and humidity on their bathrooms. In fact, a typical shower can produce a pint of water in the form of humidity. In very cold or hot weather, we don't typically open windows, so the damp air can't escape. Lingering damp air can wreak havoc; over time it can cause paint to peel, doors to warp, and may even lead to mold growth.

To reduce humidity and make the bathroom more comfortable, damp air must be quickly and efficiently removed from the room. The best practice is to install a bath exhaust fan that is quiet and properly sized to the room dimensions. Additionally, it should have a feature that enables it to be controlled on a timer. Bath exhaust fans are a type of spot ventilation, which removes moisture and pollutants at the source where they're generated. Spot ventilation is also used in the kitchen.

Here are some things to think about when choosing and installing a bath exhaust fan:

How quiet is it? Many homeowners don't use exhaust fans in the bath because they can be loud and annoying. By choosing a quiet bath fan, chances are the homeowner will use it more often. Fan loudness is measured in "sones." The lower the sone, the quieter the fan is. The best fans have sound ratings of 0.5 sones or less. Units that produce more than 4 sones or more should be avoided. Small bathroom fans (less than 76 cfm) must have sound levels of no more than 2.0 sones to be labeled as Energy Star compliant; large bathroom fans must have sound levels of no more than 1.5 sones.

What's the capacity for air flow? Fan exhaust capacity is rated in liters per second (L/s) or cubic feet per minute (cfm). A standard 5 x 8 bathroom needs a good-quality fan that draws a minimum of 50 cfm. Larger master baths may require stronger fans to efficiently pull the humid air from the room. To calculate the size of fan needed, use this equation: Multiply the total cubic feet of the bathroom buy 8. Then divide that number by 60, and you'll get the required cfm. This equation is based on recommendations from the Department of Energy's Energy Efficiency and Renewable Energy (EERE) program.

Is the exhaust fan equipped with an electronic timer? In general, bath exhaust fans should stay on for one hour after baths or showers to effectively remove excess moisture from the room. Bathroom fans connected to light switches or exhaust fans that have a simple "on/off" switch normally won't run as long as that because the homeowner doesn't think about the real function of the fan. Also, homeowners may not remain at home long enough to keep the fan on the recommended amount of time. A fan equipped with a timer will ensure the fan remains on as long as needed to exhaust moisture.

An electronic timer is usually quieter than a mechanical timer and offers a wide range of settings. Make sure the timer setting instructions are easy to understand and the timer itself is easy to operate. Use a delayed fan shutoff to keep the fan running for at least one hour after the homeowner leaves the room. Other options include a motion sensor that activates the fan when someone is in the bathroom.

Where in the bathroom should the fan be located? Because exhaust fan will inevitably exhaust clean room air along with moist air, locate exhaust vents as far away as possible from space heating and cooling registers. This will minimize the amount of conditioned air that is directly exhausted out of the bathroom. When mounting bath exhaust fans remember to seal the gaskets and fan houses mounted on ceilings to reduce gaps that could result in air leaks. In insulated ceilings, use fans that are rated for insulation contact.

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