The 91-013 is the 20” x 20” x 5” replacement Progressive Media air filter for the following Ultravation models:

Progressive Media Straight-Through Design
Whole House Air Cleaner models:
90-016

Photronic Straight-Through Design Multistage
Whole House Air Cleaner Models:
92-031, 92-032, 92-033, 92-121, 92-122, 92-123

The 91-013 replacement filter uses Ultravation Progressive Media Filtration with Ultrastrand fiber technology, which meets and exceeds MERV 11 (ASHRAE 52.2) performance standards. Ultravation MERV 11 filters can capture particles as small as .3 microns in size. The specially shaped surface of an Ultrastrand fiber captures and holds particles far better than the typical round fiber. To increase capture ability still further, Ultrastrand fibers carry a permanent electrostatic charge that attracts particles like a magnet.

Ultravation Progressive Media design increases fiber density from the upstream to downstream side, gathering the largest particles in the first part of the filter, while progressively smaller particles are captured through the filter. As a result, the media becomes filled edge to edge, providing very high dirt holding capacity.

The manufacturer recommends you change the filter every 6 months under normal operating conditions.