There are several important layers of function in these things: the cells, prefilter and charcoal filters, for example. Also they require the fan to be running constantly to effectively clean the air. Most of them I see are a shambles. The above video gives you the instructions for proper maintenance.

The filters below are a fallback solution: low tech replaces high tech if all should not go well...click on image for link.

#HVAC #ventilation