Abstract: An across the wall pressure differential indicating apparatus comprising a wall duct having first and second open ends, first and second mounting plates respectively attached to the wall duct at the first and second open ends respectively, a low speed airflow indicator adapted to indicate a pressure differential and mounted in fluid communication with the wall duct such that substantially all airflow passing through the wall duct also passes through the indicator, and an intumescent material disposed in the wall duct between the first and second ends.

Abstract: A pressure differential indicating apparatus has a wall duct with first and second ends, first and second flange like mounting plates respectively disposed around and attached to the first and second ends, a low speed airflow indicator mounted at one of the ends on a side of the mounting plate opposite that to which the wall duct is mounted, and a fire damper with a closable fire damping door that is disposed in the duct. The fire damper includes an actuation device for keeping the door open until the actuation device is caused to close the door. One particular embodiment of the actuation apparatus has a spring counter loaded solenoid that keeps the door open when energized and a spring operably connected to the solenoid so as to close the door when the solenoid is de-energized.