With some exceptions, such as the impressive growth of The Yankee Candle's brand, Fragrance Spheres, passive diffusers
are giving way to power-operated devices under the active segment that increased by nearly 5%.
Sizing of air terminals and determination of the number and location of passive diffusers
should recognize that Type II leakage will contribute a significant amount of uncontrolled conditioning air to the space.
"They typically are less fragrant than a scented candle or electric plug-type fragrancer, but more robust than potpourri, fragranced gel, and other passive diffusers
. Additionally, they have the advantage of portability and flexibility (they don't need a plug), ease-of-use (don't need to light) and aesthetics (fits any room decor)."