Ventilation Fans: the New Energy Hogs?

Table 3 on page 18 lists the efficiencies of the quieter ventilation and exhaust fans used in American homes. The table reveals a major scandal regarding the status of residential mechanical ventilation: all of these fans are pitifully inefficient. Only a few (mostly manufactured by Panasonic) have efficiencies above 10%. This is surprising because the manufacturers have invested significant re-engineering effort into making them quieter.

These low efficiencies weren't a problem a decade ago when most fans were operated for brief periods. The small power draw of a fan multiplied by the few hours per year that it operated did not consume much electricity. It didn't pay to invest much in improving efficiency.

But the situation has changed. New homes rely increasingly on controlled ventilation instead of haphazard air infiltration to provide fresh air. As a result, fans now operate many more hours-and sometimes even constantly-to maintain adequate air quality. One builder of new homes placed the switch for a ventilation fan in the attic to discourage the occupants from turning it off. More fans are also attached to lights and sensors. The small power draw of a few fans multiplied by many hours per year of operation translates into a significant amount of electricity. An efficiency improvement can save a lot of energy (especially when one starts from such an abysmally low level).

Is it easy to improve a fan's efficiency? Yes and no. Small fans typically use shaded-pole motors. These are the least efficient motors made but they have one redeeming feature: they are dirt cheap. It is a simple (but more expensive) matter to switch to more efficient motors. The fan blades and housings themselves can also be redesigned so that they move more air per unit of energy invested. Finally, the whole ventilation system holds potential for improvements, including the ducts and the grilles. These techniques for improving fan efficiency are pretty well understood, but they haven't been applied systematically to small fans.

There are still millions of fans operating less than 100 hours per year. Realistically, not many improvements can be justified for these fans. But there are millions more for which efficiency improvements are justified. Consumers deserve-and will pay for-fans that are both quiet and efficient.

Home Energy can be reached at: contact@homeenergy.org
Home Energy magazine -- Please read our Copyright Notice