internal enclosed environment via positive pressure port 28 the magnahelic gauge 10 determines the difference between the two and displays that differential pressure therefore any positive pressure reading on the magnahelic gauge 10 indicates a higher air pressure in the interior environment than the external environment typically the magnahelic gauge 10 can measure a pressure differential in the range of 0 2 inches of water column inches wc in one embodiment of the present invention the positive pressure reading is in the range of 0 5 to 0 7 inches wc referring now to fig5 the window 38 is to be left open about 6 inches to allow for a window sealer made of plexiglas or other type of weather resistant material 46 to fill in the 6 inch opening a 3 inch hole cut out of the plexiglas for the hose 7 from the air intake port 6 on the filtered positive pressure air unit 100 will go through the hole to accept outside air dirty air 12 in another embodiment an appropriately sized flanged bracket can be attached to the window sealer 46 to accept the hose 7 the hose 7 will be sealed to the hole and the window sealer 46 will.