By Paul Bianchina
One of the most important fixtures in the bathroom is also one of the least expensive and least noticeable - the ventilation fan. Mounted in the ceiling or in the wall, ventilation fans help rid the bathroom of odors and, more importantly, of potentially damaging moisture.
There are really four things you need to be concerned about in the selection and installation of a bathroom ventilation fan - air movement capacity, noise level, ducting and optional accessories. Each plays an important role in the fan's proper operation.
Air Movement Capcity
Ventilation fans are rated as to the amount of air they can move in cubic feet per minute (CFM), and determining how large a fan you need should be your first consideration.
First, you need to measure the air volume in the bathroom, which is simply a matter of the room's width times its length times its height. For example, if your bathroom is seven feet by 10 feet and has an eight-foot high ceiling, multiply 7 x 10 x 8 to arrive at 560, which is the number of cubic feet of air in the room.
For effective ventilation, a fan should have the capacity to completely change the air in the bathroom about 10 times per hour. For 560 cubic feet, the fan needs to move about 5600 cubic feet of air per hour (560 x 10 air changes per hour). Remember that ventilation fans are rated in cubic feet per minute, so you need to divide by 60 to convert the cubic feet per hour to cubic feet per minute. In this case, you would need a fan with a capacity of approximately 93 CFM (5600 / 60). You won't find a fan with that exact capacity - 100 CFM will probably be the closest.
Noise Levels
In order to be effective, a bath fan needs to be used, and that usually won't happen if it's too noisy. For that reason, the second consideration in the selection of your fan should be the amount of noise it makes while in operation.
In addition to the CFM rating discussed above, ventilation fans also carry a noise rating, listed in sones. Several things affect how loud or quite a fan is - its air-moving capacity, the type of fan blade assembly being used, how much insulation is placed in the fan housing, and where the fan is located. As you probably would expect, the quieter the fan is, the more you can expect to pay for it.
For the 100 CFM fan in the example above, the lower cost models will have a sone rating around 4.0 to 4.5 with a cost of around $40 to $50. At the quieter end of the spectrum, you'll find ones rated at a much quieter 2.5 sones, and the price goes up to about $100. Fans are a long-term investment, and the quieter unit is well worth the extra initial cost.
Installation and Ducting
Most fans are designed for direct ceiling mounting within the bathroom itself. There are also fans designed to mount in the wall, and fans, which mount in a remote location - up in the attic, for example -- to further cut down on noise.
The typical bathroom exhaust fan is basically a square metal box with two adjustable arms attached to it. The box contains the fan motor and blade assembly and a round outlet port for ducting. The two adjustable arms attach to the ceiling joists to support the fan in the desired location. A decorative grill covers the fan and completes the installation.
Remember that the primary function of a ventilation fan is to get rid of moisture, so it's crucial that the unit be vented all the way to the outside of the house. Venting a fan into the attic simply takes the moisture from the room and puts it up into the attic, where it can do just as much long-term damage to your house - it's also a violation of the building codes.
Most fans used in residential bathrooms have a 4" outlet port, which allows for easy connection to 4" solid or flexible metal ducting - the use of flexible 4" dryer hose is also not allowed by the building codes. The outlet port also contains a one-way spring-loaded damper, which is simply a weather-stripped metal or plastic flap that opens when the fan is turned on, and then closes again when the fan shuts off to prevent cold outside air from coming back into the room.
The exhaust ducting needs to run to a screened and covered opening in the roof, or to a screened opening in the blocking between the trusses or rafters - the dealer where you purchase the fan can help you select the right type of ducting and cap for your particular installation. Remember to install the ducting in a smooth run with no low spots where moisture can condense and accumulate.
Options
Fans are available as a fan only; a fan/light, which combines an incandescent or fluorescent ceiling light with the fan; a fan/heater, which combines the fan with a forced air heater or one or two heat bulbs; and a fan/heat/light, which combines all three. You'll also have a number of options for how to control the unit, ranging from a single switch that turns on the fan and light at the same time to multiple switches that control each function separately. You can use a simple dial timer to ensure that the heater or fan shuts off after a certain number of minutes, or a 24-hour timer that turns the fan on and off at preset times to help with ongoing ventilation needs. Finally, you'll find a number of options for the grill, ranging from plain white plastic to brass, gold and wood trim.
Ventilation fans are available at home centers, plumbing and electrical stores, as well as a number of discount stores and other retail outlets.
Copyright 2000-2006 Inman News Features. Distributed by Inman News Features.
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