After you defeat Heat Man, or if you happen to have his weapon, go to Crash Man's stage. In the very first area where you are teleported, climb the first two ladders, jump on the highest pipe, and select the Atomic Heat. Run to the wall and begin pressing A + B rapidly (try not to charge), jumping and shooting facing the wall. You must have some Atomic Heat weapon energy in order for it to work. If it does not work and you cannot fire anymore, just get a weapon refill from the enemies around that area and try again. If done correctly, your Atomic Heat will automatically refill itself and you will never run out no matter how long you charge. This trick will not work on any other stage or using any other weapon.