Was wondering if there're one-way return vents that I can install to
allow
the cold air to be sucked into the vents when the blower/heater's
running and
NOT allow cold air to escape the other way (back into the room) when
the blower's
idle.

For some reason, when the blower's not running, there's cold air
coming outta return vents - a whole lot of it. Figuring out where it's
coming
from is a whole different task.