Efficiency of Computers as Heaters

If you plug in a bunch of old computers and turn them on and run something like a continuous defragmenter to get a lot of activity, will it heat up a room as efficiently as a space heater that uses the same amount of electricity?

If anything it would use more elecricity, because computers today are just starting to become more energy efficient, but I supposed if one of the computers overheat and light on fire then it’s really efficient

Yep. Virtually 100% of the energy is turned into heat. No different from a space heater, really…

More heat comes off the monitor than the tower.