storm slider said:
Is heat a big factor that shortens a CPU's lifespan?
It does, but it's not linear. Temperatures below 70 degrees centigrade are fine and the CPU should last for many years. However, temperatures above 90 can have a negative impact on the lifespan of the CPU or GPU if they are sustained for long periods of time. Most processors have a thermal cutoff which throttles the affected core if it gets too hot.