The idea of stacking air filters is a tricky proposition. With all these HEPA filters on the market , one may think a better flow can be achieved and better quality of air as a result of finer air-filtration in an existing system. Not unless you have a clean duct system that includes a clean return duct to the furnace/Air blower unit. You can over heat the motor and blow a circuit if you’re not doing it properly. My question is : why are there so many systems with so poor return ductwork ? The filter at the blower exchange on the system picks up all the crap in the walls ! Cobwebs, dust bunnies, insects, hairs, plaster powder, you name it ! You can’t improve air quality by just putting a HEPA filter in that Return environment! What are these installers thinking . Just as long as the Mfg. unit has its filter in place , that meets the warranty requirement ? The HEPA filter is going to clog up , like tomorrow ! With a closed system, wouldn’t it be a whole lot cleaner ? The mfg required particle filter size at the unit could be maintained while a second closer monitored HEPA filter could be at the register upstairs. Wouldn’t that be efficient and cleaner air all around ?
My friend said her installer poopahed that and said she’s jeopardizing the system. Meanwhile the return filter gets all this dirt from inside her open wall duct channeled through her house ? That’s a pretty powerful blower too. I say this because we put a filter upstairs and it’s cleaner than the filter at the unit downstairs. The problem was the unit filter clogged anyway and the breaker blew !