I have some questions regarding my residential HVAC system.

First, the supply and return ducts are made of sheet metal and sized 7"x22". What is the CFM capacity of that size duct? Is there a max size of furnace and air conditioner that should be connected to that size duct?

Second, my system has an Aprilaire 700 humidifier installed in the side of the indoor coil cabinet. Is this an acceptable practice? Are there any long term impacts to the coil with this type of installation?