The blower motor is the fan that pushes heated or cooled air out of your furnace or air handler (the indoor cabinet) and through the ducts to each room. Without it, the equipment would make hot or cold air but never deliver it. It runs more hours than any other motor in the system, so its type shapes both your comfort and a large slice of your electric bill.
There are two main kinds. Older systems use a PSC (permanent split capacitor) motor, which runs at one fixed speed and is roughly 60% to 65% efficient. Newer systems use an ECM (electronically commutated motor), an electronically controlled motor that varies its speed and reaches about 80% efficiency or higher. The ECM's adjustable speed means longer, gentler runs instead of blasts at full power.
A federal rule pushed the industry toward ECMs. Since July 3, 2019, the Department of Energy's furnace-fan standard means new residential furnaces ship with electronically commutated motors. So most equipment sold today already has the more efficient motor; the PSC question mainly comes up when you repair or keep an older system.
For a buyer, the blower motor matters in two ways. A failed motor is a common repair, and an ECM replacement part costs more than a PSC but uses less power and runs quieter. On a new system, a variable-speed ECM paired with a multi-stage compressor gives the steadiest airflow and the best humidity control — worth the premium in a humid climate, less so in a dry one.