Hope this is the right area for this question;

I have several glass tanks that I use to house my frogs, one giant pixie, one dwarf pxyie and a fantasy horned frog, and use heat mats on rheostats on them. I have had a couple of them now since 2007 and was wondering if there is a 'lifespan' or recommended time to replace the mats? I haven't had any issues at all and installed them as the manufacturers stated with the tanks elevated to allow excess heat to escape and have made sure not to rest the edges of the tanks on the electrical wiring. In addition I have them plugged into power surge type power strips and have not overloaded the outlets, but I am conscious of a potential fire risk.

If anyone has any insights on this I would very much appreciate it, thanks in advance.