Tjernlund Products. The XChanger’s two reversible 90-cfm basement fans vent stale air to the outdoors, draw fresh outside air into the home, or do both when positioned in opposite directions. The dual fans use 35 watts and automatically turn on or off via a humidity detector. The unit is available with an optional timer control, fan speed control, and a duct take-off for ventilating adjacent rooms. 800.255.4208. www.tjernlund.com.