Hatching?

[Yorkshire Coop]

A rotten egg could explode but all eggs should be warm in the incubator.

 

[Ridgerunner]

Would an egg explode if it is dead or would it be cold?

Everything in the incubator should be warm.

Whether the egg has a living embryo or is dead has nothing to do with it exploding. If bacteria gets inside it multiplies. If there is a living embryo inside the multiplying bacteria will kill it. That is a common myth on this forum, that a living embryo makes a difference, but it doesn't.

Not all eggs that get bacteria inside explode either. That's another myth. Pressure will build up but quite often a slimy smelly fluid leaks through the porous egg shell. No explosion.

If you smell the rotten egg smell in the incubator you have a rotten egg. If it is not obvious which one it is, sniff them individually and carefully remove the bad one, they can actually explode so be careful. It is absolutely horrible when you get one but very few people actually ever experience that. I never have in an incubator but did once under a broody hen.