Air Handler Closet Dimensions . The code here in tucson requires an additional. As its name suggests, an air handler “handles” the air. Air Handler Closet Retrofit Building America Solution Center from basc.pnnl.gov This is for a 2200 sq ft residence. According to experts, there should be at least 6 to 8 inches of the gap from the closet walls to the actual hvac system on both sides. 4 for an air handler installed in a closet with a louvered return opening, the minimum open area for the louvers will be as shown below.