One could argue that it is 100% as every Watt that enters through the socket (not counting reactive energy) is going to become heat at some point in the very near future, including the air moved by fans, the photons emitted by the screen, etc etc.
Not really? The best heaters are heat pumps which can under typical operation reach 300-500% efficiency (COP). Technically they aren't converting the electricity into heat, but for arguments sake here about heaters we only care about electricity consumed to heat generated.
The 0.1% mentioned might be the light that the project produces.