In the photo there are two vent openings on the living room floor. One is a supply vent and one is a return vent. When vents like this are so close together they aren’t very efficient because they just cycle the air from one vent to another and not through the living space of the house. The air from the HVAC system is meant to condition the air in the house and not just cycle through the vents. In this case there must have originally been a wall that divided two rooms near where these vents (now in the floor) are. When a house is remodeled or walls are removed it is important to take into account the duct work system and air flow in the house.
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