I’m looking for a hepa exhaust filter to put on a 6" inline duct fan to have an air filter. I need hepa or merv 13 or higher rating. I know this will slow down airflow, that’s why I’m adding the inline duct fan too.

Initially I got 6" to 8x8 register box to put an 8x8 merv13 filter in, but there’s too much space around the filter and the register boxes don’t fit together. I’d prefer avoiding the register if possible, I’d prefer an inline filter.

Does anyone have suggestions for a hepa filter that could fit directly over a 6" inline duct fan?