An episode of ask Google webmasters, Google’s John Mueller answer a question about multiple h1 headings and how to handle them.
This is a pretty common question and it’s pretty straightforward. Google doesn’t have a problem when it comes to multiple h1 headings on a page that’s a fairly common pattern on the web. Google uses headings to better understand the context of different parts of a page. Having clear semantically understandable headings is useful in understanding any given page. However, Google has to work with the web as Google find it and a lot of it isn’t semantically structured at all.
For users, the difference is minimal. Both kinds of pages can be extremely relevant to a question that they have. In turn, Google isn’t too picky and try to work with the HTML as we find it; be it one h1 heading, multiple h1 headings, or just styled pieces of text without semantic HTML at all.
In short, when thinking about this topic, SEO shouldn’t be your primary objective. Instead, think about your users if you have ways of making your content accessible to them; be it by using multiple h1 headings or other standard HTML constructs, then that’s not going to get in the way of your SEO efforts.
As usual, John Mueller did not give a clear answer to the question. What he was basically saying is mark up your site any way you want for humans and not for search engines. The Google algorithm will see your page the way humans do. Use multiple H1s if you like but one of them has to be dominant in terms of visual layout to establish what the whole page is about.
They’ve made it clear repeatedly that the content of your site most determines how SEO is handled for your site. How it’s structured internally shouldn’t really even be a factor. That said, HTML coders should be advised to use a single H1 on a page, and sub-headers for other, less important sub-topics.