When a resistor is rated at "3W" or "5W", that means it's capable of that level of power output, while in free-air, while maintaining it's properties within it's specification. We don't care so much about it staying within a 5% tolerance of it's rated values and are mounting it into what ammounts to a large heatsink, that has the effect of allowing it to survive a much higher power than it's specified rating. Usually they are wirewound resistors, since wirewounds tend be a lot more abuse-tolerant than other type.
My hot-end is a home-built one and it uses a 3.9Ohm 3W resistor on 12V, so it's actually running at well over 30W.
My hot-end is a home-built one and it uses a 3.9Ohm 3W resistor on 12V, so it's actually running at well over 30W.