How to export a render as an item to add to a comp?

I made a fire animation, and I want to export it in such a way that I could add it as a tool in the node viewer (if possible). Whats the best way to export/save your comps to add into other comps?
https://forum.blackmagicdesign.com/
https://forum.blackmagicdesign.com/viewtopic.php?f=22&t=29949