If you're reading this blog post chances are you're either one of our loyal followers (thank you very much) or you purchased a Com-Pak, Com-Pak Bath, Com-Pak Max or Energy Plus and are wondering "What the heck do I do with these little foam thingies I found inside the box?" If you're in the later group, this blog post should answer all your pressing questions. So we do mention those foam thingies in our owner's guide -- we call them "rubber shims."
Of course, that is easy to miss because there's a lot of info in our owner's guide. But here's the TLDR version: They can be used to fill in gaps between your stud and the wall can. Our wall cans are ever so slightly tapered towards the back. The shim should be placed on the back of the can on the side facing the wall stud.
The foam helps keep the can and heater assembly secure and aligned, because it only attached on one side. Our engineering team says that it will also help dampen vibrations when the motor is running. So there you have it. Don't put them between the heater and the wall can, behind the motor or anywhere else for that matter. They just go between the stud and the wall can or directly into your garbage can.