Cold Air Return - near ceiling

[HDVH2024]

Looking for help regarding cold air returns on the 2nd floor of a 35 year old 2 story house, approximately 2200 sq feet; newer natural gas furnace. The cold air return registers on the 2nd floor are in the wall approximately 12 inches down from the ceiling. The cold air returns on the main floor are about 8 inches up from the floor. Since cold air falls shouldn't the 2nd floor cold air registers also be just above floor level? The 2nd floor is 2 - 3 degrees colder than the main level, Fall / Winter / Spring. With the cold air returns up high I expect that they are sucking out the hot air from the floor heat registers. Should blocking the 2nd floor cold registers during the heating season help to increase the 2nd floor rooms warmth?   

[InfinitudeMECH]

Cold air returns provide two functions, they are cold air back to the furnace to be heated when the furnace is in heat mode.

In cooling mode, they are a path for warm air back to the evaporator coil, for that airs heat to be removed. 

Cold air returns in the low wall orientation on the main floor are usually standard, main floor areas almost never have a thermal stratification issue with temperatures. 

High wall returns grills are normal in 2nd floor installations, as hot air rises.  Being in the high wall orientation, the rooms with return grills are self stirring per-say.  2nd floor levels are always an issue with cooling, hence the high wall return placement. 

You can purchase additional return vents for your 2nd floor and install them, some grills offer shutters than can be opened and closed.  High wall grill open in cooling, low wall grill closed in cooling,  high wall grill closed in heating, low wall grill open in heating.  But given your situation, you will always have a temperature difference between main and second floor, thermostat being on main floor which drives the temperature of the house, the one square foot of air space around the thermostat is a educated sample of what temperature your house temperature should be. 


Thermostats with multiple averaging sensors can be installed as well,

[HDVH2024]

Thank you for your explanation. I've blocked the 2nd floor ceiling returns for the heating season. Will remove the blockage when we return to hot weather again. Also added 18 inches of blown insulation to the attic to help with heat / cooling retention.