Hello, here I’m rendering smoke and as it takes some time to render
But why does the rendering part take some much time rendering the transparent background (orange brackets)…doesn’t blender know that there is nothing there so it should just render it out fast with no problems. In my case it takes as much as the smoke, and I don’t know why? Can anyone help me?
And does anyone have any advice/tips to speed up the rendering in smoke. Current frame can take to 1 minute and more.
This is normal behavior, it is part of the smoke domain, so there is volume in there even though the density is “set” to zero (by some multiply node) and you can’t see it.
I figured, but in other software where I use simulators and they have the domain, this doesn’t seem to be a problem and rendering is much faster. I hope they look at PhoenixFD and others for improving in this matter.
Thank you for you reply tho 
Are you using “adaptive domain” for your smoke?
I don’t think Cycles actually knows if there is any smoke or not in the area it is rendering within a Domain, until it fires rays through the smoke.
To get around this, try one of the builds with adaptive sampling. That stops working on a tile when there is no visible changes after x passes, works great for smoke rendering for me as it would almost instantly stop rending an empty tile in your situation.
@ Kauranga Yes and high res smoke
I’m not using cycles.