BBQ raises your carbon footprint. And the heat contributes to global warming.
The truth is with any BBQ the top should stay fully open all the time. You control the air flow with the bottom vent. Fully open will allow more air to enter the coal area, thus burning hotter.
Hot air rises, leaves the top vent and thus sucks new air in through the bottom. Being a lib you should know all about hot air...and sucking for that matter
.