By design, filters allow some percentage of particulate to pass through the HVAC system. Retro-installation of high efficiency filters (HEPA or ULPA) to address this situation is ineffective because:

• the higher air flow restriction of these filters increases differential pressure
• the HVAC system requires major modification to accept the filters

A typical VIGILAIR® system uses high filtration filters that yield a minimum of added pressure to the HVAC unit. VIGILAIR® systems are designed so that in most cases the pressure increase of high efficiency filtration is completely compensated by a pressure decrease caused by clean, irradiated cooling coils.

HEPA White Paper

If you have HEPA filtration, you're free from airborne contamination, right?  The idea that HEPA filters provide 'absolute' protection from microbial contamination is absolutely not true.  Find out why by down loading our White Paper, "The Myth of HEPA."