Check out some similar questions!

shader · Feb 20, 2006, 01:59 PM

Each one of my bedrooms has two cold air returns. One is located near the floor and has a grill that can be opened & closed. The one located near the ceiling is just a grill. I know hot air rises, cold air is heavier, etc. When should the bottom one be opened or closed-summer/winter seasons? Should the top one also be able to open close, or is the plain grill OK? :confused:

labman · Feb 20, 2006, 02:07 PM

I would open the bottom ones in the winter and let the coldest air return to the furnace. I guess it wouldn't hurt to have ones at the top you could close as long as you never close both. Nothing you have to do.

shader · Feb 20, 2006, 02:12 PM

Thanks, labman-just one less thing to do!!

Frank Mangrum · May 13, 2012, 11:21 AM

Originally Posted by labman

I would open the bottom ones in the winter and let the coldest air return to the furnace. I guess it wouldn't hurt to have ones at the top you could close as long as you never close both. Nothing you have to do.

Frank mangrum-The system would operate more efficient if return air was pulled from the upper return in heating mode assuming each return was sized to handle total air requirements of area to be heated. Since heated air stratifies at ceiling it is wise to pull this heated stratified air back to the heating unit to be reheated to a higher temperature than the cooler air from the lower return. This higher output temperature will heat room faster and it utilize this much warmer stratified air at ceiling to do so-this saves energy.

Frank Mangrum · May 13, 2012, 12:01 PM

Originally Posted by Frank Mangrum

Frank mangrum-The system would operate more efficent if return air was pulled from the upper return in heating mode assuming each return was sized to handle total air requirements of area to be heated. Since heated air stratifies at ceiling it is wise to pull this heated stratified air back to the heating unit to be reheated to a higher temperature than the cooler air from the lower return. This higher output temperature will heat room faster and it utilize this much warmer stratified air at ceiling to do so-this saves energy.

The lower return should be used in the cooling mode to return the cooler air at floor level back to the cooling coil which will be cooled to a lower temperature as it passes through cooling coil as opposed to using the upper return that has much warmer stratified air temperature. The goal is to allow heat to stratify in ceiling area after all we are trying to keep people comfortable not the ceiling. When people are seated they only occupy the lower half of the room, we will call this the comfort zone. This techique will keep the comfort zone cooler while leaving the stratified warmer air near the ceiling alone which will reduce cooling demand on the cooling system- this saves emergy