How To: Install a Bathroom Fan
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Replacing or installing a bathroom fan will keep mold, mildew, and odors away. Here’s how to determine the size and type of fan you need, and what you need to DIY the project.
Bathroom fans don’t have to sound like a jet engine to remove enough moist air to keep your bathroom mold- and odor-free. In fact, a loud bathroom fan may signal just the opposite: inefficiency. The latest bathroom fans are so quiet you can barely hear them run, yet they remove just as much air (if not more) than your old rattletrap—and they’re more energy efficient too. While most homes that are at least 20 years old have bathroom fans that consume about 125 watts of energy and rate 5 to 6 sones (roughly five times the noise of an average refrigerator, which rates only 1 sone), today’s fans range from a $100 model that uses around 55 watts and rates 1.5 sones to a super-quiet 0.3-sone model that uses just 5.8 watts and costs around $200.
Switching out your bathroom fan for a newer, more efficient model means you’ll be able to run it longer to remove more humidity and still save money on your energy bill, all without the nuisance of an obnoxiously loud roar. You may be apprehensive about taking on the installation yourself, but don’t let fear hold you back. This guide to installing a bathroom fan will set you on the right course.
Key Considerations Before Replacing or Installing a Bathroom Fan
Taking on any home renovation project can be challenging and rewarding, but before you decide to replace or install a bathroom fan, there are several factors to consider, including whether a permit is necessary, the type of bathroom fan that you need, and both the size and style of the existing bathroom fan.
Determine Whether You Need an Electrical Permit
A permit is an official government document that gives a person or company the authorization to perform certain work. It’s commonly used by local governments to ensure that any work performed on a home or commercial building is safe and appropriate and takes into consideration the age and condition of the existing structure, the age of the electrical system, and local laws that may inhibit significant changes to a building.
A bathroom fan requires an electrical circuit for the fan as well as ducting to carry humid air to the outside of the home for proper ventilation. This work will likely fall into mechanical and electrical categories, which generally require a permit. It’s important to note, however, that every city has somewhat different guidelines for permits, so check with your local municipality to determine if you need a permit for this work.
Determine the Type of Fan You Need
Bathroom fans can be separated into three types: ceiling-mounted, wall-mounted, and inline fans. It’s important to know what type you already have before choosing a replacement.
- Ceiling-mounted bathroom fans have a self-contained fan unit that pulls air in from the bathroom and pushes it out through ducting that runs up to and out through the roof. This is the most common type of bathroom fan.
- Wall-mounted bathroom fans are essentially the same as ceiling-mounted fans, except they are mounted in the bathroom on an exterior wall of the house, and their exhaust ducting runs out through the wall instead of the roof.
- Inline bathroom fans have one or more exhaust ducts that run to the various bathrooms in the home. The actual fan, however, isn’t installed in the bathrooms but rather in a remote location, such as an attic. These fans are typically much larger than ceiling- or wall-mounted fans because they need to be powerful enough to provide adequate ventilation to multiple bathrooms.
Select the Right Size and Style of Fan
Bathroom fans come in several sizes, from small units that exhaust just 50 cubic feet of air per minute (CFM) to larger units that remove almost 200 CFM. It’s important to choose the proper fan size from this wide range. A fan that’s too small won’t remove enough odor or moisture, leaving your bathroom subject to mold, mildew, and peeling paint. One that’s too big could, in some instances, contribute to a dangerous negative air pressure situation that could pull deadly carbon monoxide back through the flue of a furnace or water heater.
To calculate the size that will meet your needs, multiply the bathroom’s length, width, and height to arrive at total cubic feet. To determine the target CFM, multiply the total cubic feet by .13 and round up to the nearest 10. For example, a 7-by-9-foot bathroom with an 8-foot ceiling equals 504 cubic feet. When you multiply 504 by .13, you get 65, so you would round up and buy a 70 CFM bathroom fan. If you have a large bathroom (600 cubic feet or more) or one with a jetted tub, it’s best to bump up fan size by 50 CFM.
Quieter fans cost more, but you may decide that the reduced noise is worth the higher price. If you have a mold problem in your bathroom, you may want to consider a model with a built-in moisture sensor that runs the fan until the humidity drops to a normal level. For easiest installation, DIYers who are replacing an existing bathroom fan should consider choosing a replacement fan with slightly larger dimensions than their current fan. Retrofit models can be installed from inside the bathroom, which saves you a trip to the attic, and their larger footprint eliminates the need to patch the wall afterward.
Tools & Materials
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