The regulations are available online, if you care. You’re looking for title 47 part 15, and you can start here: [Title 47 part 15.
A couple of clues to help you with this mess:
Class A and Class B are defined in 15.3 (Definitions, how logical is that?). If it’s “marketed for use by the general public” it’s Class B, and standards are stricter.
Intentional Radiators: it is supposed to radiate RF energy. It’s a Radio!
Unintentional Radiators: it radiates, but not in order to communicate. It’s a TV receiver or a computer or something of that ilk. It’s Not A Radio (but it radiates)!
Have fun! The Real Answer ™ to any question you might have is in there. As you can see if you look at the regulations, it’s not really easy to summarize.](http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=2a611d3b89795659895a0caf303c2f01&rgn=div5&view=text&node=47:1.0.1.1.14&idno=47)