Rxvt and Inconsolata (a font)

From the man page:

CHANGING FONTS Changing fonts (or font sizes, respectively) via the keypad is not yet supported in rxvt-unicode. Bug me if you need this.

   You can, however, switch fonts at runtime using escape sequences,

e.g.:

      printf '\e]710;%s\007' "9x15bold,xft:Kochi Gothic"

   You can use keyboard shortcuts, too:

      URxvt.keysym.M-C-1: command:\033]710;suxuseuro\007\033]711;suxuseuro\007
      URxvt.keysym.M-C-2: command:\033]710;9x15bold\007\033]711;9x15bold\007

   rxvt-unicode will automatically re-apply these fonts to the output so

far.

Depending on the shell you use you could assign those to keyboard shortcuts. In zsh you could define a shell function and use bindkey to bind it to an alt-key for example.