In the past, a common way to return air back to the air conditioning system was to use the wall cavity. An intake register would be placed near the floor and the air would travel between the studs and drywall up into the attic where a duct would take the air the rest of the way. The wall cavity is not complete sealed and you end up with the following:
- Dust and debris – Dust and debris is pulled into the air system from inside the walls and attic, and will come out of the supply air vents or get stuck in the air conditioner (See attached picture). Also because the intake is low to the ground it tends to pull in more dust and debris which would have otherwise settled on the ground and been cleaned up by a vacuum or floor cleaner.
- Increased humidity – Humidity is pulled in through the walls and attic. It cycles through the air conditioning system and is introduced into the home.
- Inefficiency – Wall returns are typically not large enough to handle the amount of air needed to cycle through the air conditioning system and will restrict air flow. When an air conditioning system is not providing its full cooling capacity it will run longer. Also, wall returns typically heat the air being returned back to the air conditioning system which is counterproductive and also causes the system to run longer. The added run time on your air conditioning system will add $$ to your utility bills.
The best thing to do is use ceiling returns in place of wall returns to see the benefits of clean air, lower humidity, and reduced utility bills.