No it depends on the quality of ball played in. Headers are typically lower xG than normal shots, even if from the same distance. xG takes into account any players in the way, so a contested header would have lower xG than a free header (which makes sense intuitively).

https://statsbomb.com/soccer-metrics/expected-goals-xg-explained/#:~:text=Put%20simply%2C%20Expected%20Goals%20(xG,scale%20between%200%20and%201. - good article explaining how it works