Ventilation fans and performance-based building codes
The 2013 version of ASHRAE 62.2 includes performance-based measurements, rather than relying on the tested performance of a fan. Under older versions you could rely on manufacturer's specifications and industry standards for duct runs.
Now, the fan installation will have to be tested by an energy rater. It won't matter what the specs say. Installed performance is the criteria now.
A problem installation with an inexpensive fan that perhaps barely met code, or a long duct run, or someone stepped on the duct during installation, may not meet the performance standards in the installation. For bath ventilation fans, the minimum code is 50 CFM, but if there's a problem, it might actually perform in the 30s or 40s for CFM.
Unfortunately, those problems are putting builders and contractors in a tough spot. If they can't fix the ductwork to meet the standard, they may have to put in new ducts or a higher powered fan.
If contractors are working in a subdivision using fans of the same type and similar installation, all the houses could fall short of meeting code. They may have to tear out fans or ducts, and no one wants to do that.
One solution is to use fans with DC motor technology, like Broan's ULTRA Smart™ DC Motor & Control Technology. With a DC motor, a fan is able to maintain its airflow even at high static pressures, and supply the required air movement levels for whole-house ventilation while meeting the spot ventilation needs of a bathroom. Multi-speed version can adjust as needed to meet the air flow requirements of a specific installation.
A fan with a DC motor helps avoid unpleasant surprises on the job site and can save contractors time and money.