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In our Bathroom Heating and Cooling for a Healthy Home article, we discussed how important these systems are for your bathroom. 

We briefly touched on ventilation, but the topic deserves an in-depth look altogether. 

Elaborate ventilation systems that duct fresh air into every room in the house are becoming more common, but a relatively simple fan mounted in the ceiling and vented to the outside can still be an excellent hedge against moisture damage and mold as well as an effective way of maintaining good indoor air quality. Even better, a good-quality fan doesn’t have to cost a fortune. 

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Fans are rated by how much noise they make, called “sones,” and how much air they are capable of moving, expressed in cubic feet per minute, or CFM. 

In a small bathroom, up to 100 sq. ft., industry guidelines suggest ventilation at the rate of 1 CFM per sq. ft. of floor area. In larger bathrooms, ventilation rates are based on the number and type of fixtures located in the bathroom. (For more information, visit the Home Ventilating Institute’s website at www.hvi.org.)

Fans located directly over the source of the moisture are most effective, so a larger bathroom with a separate tub and shower might have one fan over the shower and another over the tub. 

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The most basic bathroom fan incorporates both the fan and motor in a housing that’s mounted in the ceiling. 

More powerful in-line fans can be located some distance away and serve more than one bathroom. 

However, they’re more expensive and typically make more noise than a basic model. 

One key to any fan installation: Never vent the fan to an attic, basement, or other conditioned space where moisture can condense on cold surfaces and lead to mold and decay. 

Make sure your builder runs the vent to the outside. Rigid pipe offers less resistance to airflow than corrugated plastic pipe. 

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What to Look for In a Fan 

Fan manufacturers use an odd metric for quantifying the sound their products make. Noise levels are measured in “sones,” units of perceived sound. 

The industry describes one sone as the amount of noise a quiet refrigerator makes in a quiet room. 

Bargain fans, the kind that builders or electricians may install if you don’t ask the right questions, may be rated at 4 or more sones.

If a fan is really noisy, chances are good you’re less likely to use it, so it may not run as long as it should and consequently will be that much less effective. 

And fan noise is just plain irritating. 

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Even though a large-capacity fan is going to make more noise than one designed for a very small bath, it pays to look for the lowest sone rating available for the fan size you need. 

Bathroom Fan Essentials 

Ceiling-Mounted Fans 

  • Often packaged with a light, ceiling-mounted units include the fan and motor in a metal housing that is recessed into the ceiling. 
  • Some units draw air through a light fixture, with no visible grill. 
  • Look for a fan with a low sone rating for quiet operation. 
  • Some can be equipped with infrared light bulbs for spot heating. 
  • Small bathrooms need only one ceiling-mounted unit, but larger bathrooms with a number of separate fixtures may be better served with two. 

Wall-Mounted Fans 

  • Good solution when framing or accessibility constraints prevent you from mounting a fan on the ceiling and venting through the roof. 
  • Ensure the unit has a screen to keep out critters. 

In-Line Fans

  • Fans are installed in the duct itself, some distance away from the bathroom, and connected to one or more ceiling-mounted grills. 
  • Can draw air from more than one room; helpful for back-to-back bathrooms, for example, or multiple grills in a large bathroom with a number of fixtures. 
  • More powerful and more expensive than simple ceiling-mounted fans. 
  • Can be noisy. 

Switches and Timers 

Bathroom fans should continue to run for 20 minutes or so after a shower to completely clear the room of moisture, experts often recommend. 

While some homeowners are good about remembering that, many others aren’t, and that’s a good reason to consider installing a timer. 

Very simple models can be set easily to run for up to 30 minutes at the push of a button. 

Programmable switches are a step up. They can be adjusted to turn on the fan for a certain amount of time every day, let’s say between 7:00 and 7:30 a.m., for those folks who are on a rigid workday schedule and always shower at the same time. 

Programmable switches also can cycle a fan on and off throughout the day, which is useful when the bathroom fan is being used in lieu of a whole-house ventilation system. 

This is an option that should be discussed with a heating, ventilation, and air conditioning (HVAC) or energy professional since ventilation requirements vary with the size and construction of the house. 

Another type of automatic switch is called a humidistat. It incorporates a humidity sensor and turns on the fan when moisture levels reach a certain threshold. 

When controlling airborne moisture levels, and not necessarily improving air quality, is the main objective, a humidistat is a hassle-free way of meeting your objective. 

Ventilation Systems that Save Energy 

Installing the right fan can be a small, but meaningful step toward an energy efficient home. (For more information on this topic, read our 13 Green Building Questions to Ask Your So Cal Contractor.)

In some ways it’s counterintuitive to spend a lot of money heating or cooling your home and then running fans to blow all that conditioned air outside. Yet from an air-quality standpoint, it does make sense, and there are ways to minimize the energy penalty. 

A heat recovery ventilator, or HRV, simultaneously draws fresh air into the house and pushes stale indoor air outside. The air streams pass through a heat exchanger so that some of the energy that would normally be lost is transferred to incoming air. 

For example, in winter, warm indoor air raises the temperature of incoming cold air from outside, lowering the amount of energy that’s wasted. 

For an air-conditioned house in summer, the process would work in reverse. (More relevant for South Bay homeowners.) 

Energy recovery ventilators, ERVs, are similar, but they also are capable of exchanging some of the moisture in the air stream. 

When to choose an HRV over an ERV (or vice versa) is not a simple question, and even manufacturers may be dispensing incomplete advice. 

While climate is a key factor in choosing between the two, it’s not the only criterion. 

Before making the decision, it would be best to read up on the subject in addition to talking with a competent professional. 

A good source of information on this subject is Green Building Advisor.

Hopefully, now you have a better grasp of bathroom fan essentials.