Personally, I work to never have to load additional charcoal. I load my charcoal ring as full as possible and do not use water. I can easily go over 12 hours and 16 is about max. If I did have to load charcoal, I would pull the middle and reload. That's not the safest way to load charcoal, but that's how I'd do it if I needed to. Thankfully, I've never had to.