Final answer:
The recommended distance to hold a blowing gun from the inside of an air filter element depends on the size and age of the filter.
Step-by-step explanation:
The recommended distance to hold the blowing gun from the inside of an air filter element depends on the size and age of the filter. An older "rule of thumb" suggests holding the gun 5 inches side-to-side and 7-8 inches deep. However, newer research suggests that it is more effective to hold the gun up to 8 diameters side-to-side and up to 15 diameters deep.