Turn the Honeywell 50100 on its side, and locate the nut on the bottom of the unit. Turn the nut counterclockwise with your hand to remove it.
Slide off the bottom cover. Inside you'll see the HEPA filter. Pull the filter out.
Locate the pre-filter package that came with the Honeywell. Open the pre-filter package and slide the filter around the HEPA filter. Insert the HEPA filter back into its place.
Replace the bottom cover, then replace the nut. Turn it clockwise. Set the Honeywell 50100 upright and plug it into the wall outlet.
Verify the Honeywell 50100 system is at least 3 feet from any wall or furniture. Also verify that it is on a flat surface.
Turn the power switch to the desired level. For optimal performance, turn it to "Turbo." For a quieter operation, turn it to "Sleep" or "Day."