It sounds harder than it was. Our furnace was on its last leg, huge, loud, and inefficient. We made sure that our replacement could handle a heavier load that a HEPA filter would add when we bought it. The second HEPA air exchange filter was an off the shelf unit, put in the room that our immunosuppressed relative worked from. We have allergies, (not serious, but uncomfortable at certain seasons) so the HEPA upgrade seemed to just make sense. Because the new furnace was smaller, making room for a thicker filter was easy. It was an easy swap. Our heating bills went down, so the payback is relatively short.