I have been debating on whether or not to install a whole house air filtration on my HVAC systems. I've read several reviews pleading their case to install or not to install. I can see how they help but based on the discussions and opinions not sure how effective these systems are. I have the media filters on my two forced air units but still see a lot of dirt on the return air vent and even on the supply vents. I've even considered buying portable air purification units.