[cinntaile]

On top of that, 20 plants won't reduce the CO2 in any meaningful way. You need a lot more of them. An order of magnitude more.

[antisceptic]

Maybe you're right that 20 plants wouldn't be enough help, but growing a plant is a real method of replacing CO2 with O2. Running a box fan with a filter taped on it isn't. That was my point.