JSF Tip #61 - What does 'com.sun.faces.responseBufferSize' do?
Note this blog is obsolete, see https://www.manorrock.com/blog/ for the current blog
If you want to determine the size of the response buffer the JSF runtime uses when buffering then the 'com.sun.faces.responseBufferSize' context-param allows you to set the size to something you want. The default is 1024 bytes, which is not big, but also not too large.
See the example snippet below which you could put in your faces-config.xml.