Ok my furnace has two filters at the base of the unit, one on each side. I want to remove them and put the filter in the return air grille. I live in a very dusty area and the return air duct work gets so dirty every year and I am tired of having to spend several hours to clean it up. I have seen other systems that had the filter in the return grille instead of at the furnace.
So my return air grill is a 25x25 unit and what I am wondering if by moving the filter to the grille if I need to change the size of the return air for some reason I am not aware of. I tried to do the figuring for needed return air size for my unit but am not figuring it out.
Here are some details
Current filters are (1) 20x25x1 on one side of the furnace and 20x20x1 on the other.
Current return air grille 25x25
Furnace is a Lennox
Model # CB19-51-3p-TXV
Serial # 5895F61762
Any help would be greatly appreciated.