The answer depends on several factors. There are different smoke absorbers, the FA-400 (and it's predecessor the 493) and the HJ3100. The HJ3100 can have from 1-4 ports in use. As more ports are used (and if longer connecting hoses are used) it will reduce the air flow causing the working distance to be decreased. The air flow in the room can have a big impact on work distance as well. If the room has alot of air movement it will decrease the working distance. As a general rule, you should be able to have a working distance of 6-12 inches.