A number of leading green building programs have adopted the ASHRAE 62.2 standard that calls for constant air movement throughout an ultra-tight new home. An energy recovery ventilator or a central exhaust system will fulfill this whole-house ventilation requirement, but a single, relatively inexpensive bath fan can do the job—that is, if it’s smart enough.

Manufacturers including Broan-NuTone, Panasonic, and Air King have surpassed this whole-home challenge with fans that leave homeowners out of the equation entirely. These units can communicate with each other; know when to cycle 80 cfm and when to drop to 40 cfm; and can factor dew point, occupancy, and humidity into how long and fast to run.

Broan-NuTone’s SmartSense technology, for example, ties fans in multiple bathrooms together via wires servicing other systems in the home to share the daily air-exchange requirement and evenly distribute airflow.

“The key is that they all talk to each other,” says Pat Nielsen, marketing manager for ventilation fans at Broan-NuTone. “Instead of one running at 60 cfm all the time, these fans will talk to each other and take turns.”

When a bather turns a fan on, it remembers how long it ran at a higher cfm and deducts the time from the home’s daily requirement. The sister fans then run less throughout the day to avoid over ventilation, says Nielsen.

“It’s great for the builder because there is no extra low-voltage wiring to install to get them to communicate,” he adds.

Meanwhile, Panasonic’s third-generation WhisperGreen fans exhaust stale air while creating a slight negative pressure to draw fresh air through the house. If the standard calls for continuous 40-cfm airflow, the installer can set it to run constantly at a low speed until its motion sensor detects moisture and boosts the power to 80 cfm. A time delay leaves it running at that level for up to an hour before slowing back down to the pre-set continuous speed.

“You have a fan that can be a whole-house indoor air quality fan but also a bath fan depending if you’re in the bathroom,” says Jim Shelton, national sales manager for Panasonic. “The homeowner doesn’t have to worry ‘Did I turn the fan on? Did I not turn it off? Am I using it enough?’ The fan does the job for you.”

With bath fans running non-stop, energy efficiency and noise level matter more than ever. A DC motor in a WhisperGreen fan draws the energy equivalent of a night light at low speed, according to Panasonic.

To meet green building standards, round-the-clock fans must operate at no louder than 1.0 sone, and some are even quieter. For instance, the AKF100D Deluxe Quiet dual-speed exhaust fan from Air King runs at a barely audible 0.3 sone in continuous mode.

Smart controls and DC-powered technology come at a premium price. But as air quality becomes increasingly important for owners of super-insulated homes, one bathroom fan can free a whole house of off-gassing, formaldehydes, chemicals, and humid air, manufacturers claim.

“More and more you’re hearing people say ‘Build tight and ventilate right,’” says Shelton.