Your HVAC system will typically have 2 types of vents: Air supply and air return vents. With Ecovent, you only need to replace your supply vents.
Here are the differences:
Air supply vents
These are the vents that push air into your room. Air supply vents are the type of vents that Ecovent replaces in your home.
How to identify typical air supply vents:
Typically the smaller vents in your home
The vents have louvers or slats behind the "grill"
Turn the system fan on; if you hold a piece of paper up, the paper should blow away from the vent due to the exiting air
Air return vents
These are the vents that pull air out of your room into return vents, and back to your heating and cooling system. You do not replace return vents with an Ecovent vent.
How to identify typical air return vents:
Typically the larger vents in your home
The vents do not have louvers or slats behind the "grill"
There is a filter connected to this vent
Turn the system fan on; if you hold a piece of paper up, the paper should be pulled towards the vent due to the air entering the vent