This type of warranty tends not to be a written one, or at least not one put in writing by the manufacturer. It comes from your local installer because the installer maintains responsibility for dealing with clogged systems. Further, you should keep in mind that most of these warranties are for specific periods of time, or are prorated based on how long the system is on your home. And when you do have a problem, keep in mind most of these companies have a crew or two just to deal with clogged systems, so your name will join the ranks on their list for service calls.