The 20″x25″x1″ Flanders flat-panel 1-inch deep furnace filter is rated at MERV 5. Referred by the industry as no more than a rock-stopper, this air filter is a poor choice for those that are concerned with air quality.

With a permeability score of 9.62 (higher means better), the Flanders MERV 5 flat panel furnace filter offers a superb pressure-delta. The lower the pressure delta, the better your HVAC system would perform, which is why many HVAC installers would usually install this filter (vs. more restrictive air filters).

With a 30-day replacement recommendation (by the manufacturer), the dust holding capacity of the Flanders flat-panel is considered as low as it gets, which often leads to even poorer air quality as the more maintenance an HVAC system requires, the more likely it would end up being neglected altogether.

The filtration performance of the Flanders MERV 5 flat panel furnace filter is horrible on every level. At the sub-micron level, this filter offers no protection (0.1% @ 0.3-1µm) and abysmal protection at the 1-3µm level (12.3%). The performance of this filter at the 3-10µm level is bad (27.3%), however, Fltest.org does not incorporate this category into the weight of our scores.