Disable screen turn off

i3wm users usually annoyed with screen getting blank issue. Screen
times out after 5 minutes of inactivity. This is actually is a
feature of X.org. X.org has screen saver and power saving features.
These settings can be seen using

$ xset q

…
Screen Saver:
prefer blanking: yes allow exposures: yes
timeout: 600 cycle: 600
….

Now to increase timeout you can use

$ xset s <time_in_seconds>

s option lets you set screen saver parameters

for example

$ xset s 900 # increase to 15 mins [900 / 60]

or if you want to disable screen saver and energy saver feature completely
use

$ xset s noblank && xset -dpms

You may restart X.