Multi-purpose flexible cover with magnetic attachment

A method of sealing over a furnace filter slot in a ferro-magnetic return duct of a heating, ventilation, and air conditioning (HVAC) system, said return duct having a generally rectangular configuration with opposite faces and opposite sides, one of said return duct faces including said furnace filter slot, which sealing method comprises:

• providing inner and outer sheets of flexible, impermeable material;
• sealing said sheets together along their respective side edges and ends, forming a sheet assembly with first and second side edges and first and second opposite ends;
• providing first and second side sets of magnet segments and sealing each said magnet side set between said sheets adjacent to a respective first and second side edge;
• providing each said set of magnets with multiple, individual, magnet segments longitudinally aligned and extending between said sheet ends in proximity to a respective sheet side edge;
• providing first and second end magnet segments;
• sealing said first and second end magnet segments between said sheets in proximity to said first and second sheet assembly ends respectively;
• providing first and second transverse fold lines each extending between said first and second side edges in proximity to a respective sheet assembly end;
• installing said sheet assembly in an installed, sealing position overlying said furnace filter slot;
• magnetically, releasably attaching said first and second side sets of magnets to said return duct face;
• folding said sheet assembly ends over respective return duct side faces along respective fold lines;
• and
• releasably, magnetically attaching said duct assembly ends to said return duct side faces by said end magnet sets.