In the US 'heya' is a normal greeting, as are: hiya, hey, hi, and hello along with other casual greetings like 'what's up' and how's it going.'

Although we typically use "g"day" and "how's it going" in Australia, it's also normal to use "heya" and other casual greetings.

"Hiya" is a standard greeting in many parts of northern England.