I am going to have to agree with mdshunk, one of the most irritating things as a service tech is not being able to rationalize with the customer when you tell them that something as simple as a filter choice caused their grief. And like he talked about on commercial equipment, they have the pressure switch that reads the differential and shuts it down if blower static gets too high. I wish they would do that myself on low and midgrade equipment, not just on the high end residential like the Infinity/Evolution (in the CBP products). That would also help when it came time to explain what happened. Thats about all i'd better say, but do people like md and I a favor, treat your equipment well.