In the picture you can see the cold air return close to the ceiling.
Cold air return in floor or wall.
This pulls the air across your body.
If you could see the air come out of the floor registers you d see it be pulled across and up through the room.
If you are in the far north or in the southern us the answer is simple.
Because your body is in this path way you get the benefit of either hot air or cold air being drawn across your skin providing you comfort.
A cold air return is for cold air other wise it would be called just a return.
The return vent pulls cold air from the bottom of the room and returns it to the furnace to be reheated and returned as warm air.
In most homes the builders will use the wall cavity as a cold air return.
Homes will either have multiple small grilles throughout or a single large grille installed in either ceilings or walls.
The supply vents should be in the floor and the cold air return grilles are high on wall.
He installed the return air vents in the wall cavity but they are only 1 inch above the floor.
That means the space between two wall studs.
Step 2 place your cold air return vents on the inside walls of buildings at the lowest point.
Supply air from furnaces and air conditioners should be on outside walls.
The problem comes when you use both heating and air conditioning.
By putting the cold air return on the floor it will vacuum up the cold air on the floor and draw down the warm air from the ceiling.
In a heating climate the return duct goes near the floor to draw off the cold air and heat it up.
It differs from a register because it does not have a damper to control airflow.
Ceiling or wall grate for return air intake or heat vents.
And at the floor.
The return air vent openings need to be on the opposite side of the room so the conditioned air is pulled across the room.
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However in one location there is a heat duct within 5 feet of the return air vent both at the floor.
He claims that this method pulls the heat down from the ceiling and warms the room.
I feel he put in the minimum return air vents.
So turn the cold air return 90 degrees through the wall so that it actually draws the air from the room next to the furnace room or from the hallway of the basement.
In an air conditioning climate the return duct goes near the ceiling to draw off the hot air and cool it down.
The function of a grille is to pull air from a room to return it to the heating or cooling system.
Heat rises to the top the cold air return is then pulling the coldest air in the room to the furnace this negative air pressure brings the hot air down and gives the room a more consistent temp.