HEPA Filters cont...
We used to have to modify the filter housing and make compression spacers to squeeze them tight together and sometimes tape the borders together in clean rooms applications to minimize leakage. The highest quality with stiff frames work best but cost more. Since they capture more dust, they clog faster and want to collapse into the coil which actually helps save the motor but exacerbates the leakage aspect. Pre-filters prolong the lifespan by capturing the bulk of contaminants but all of this adds to cost and labor. Seems like a band-aid for sure with no guarantees. When you start replacing motors that burn up, everyone freaks out because it always happens late on a Friday and not a replacement in stock. 20 years as a building engineer provides a thousand examples like this.