One of the early hand vacuums from the late 1920s or early 1930s, either a Eureka or Kenmore, I don't recall which now, had what was probably the most successful hair dryer attachment for a vacuum cleaner -- successful because it contained a heating element in it.
It was not a hair drying bonnet or helmet but rather a hand-held blow-dryer. The way it worked, as best I recall, was that a heating element was affixed to the blower end of the machine, then a short electrical cord leading from it was plugged into the side of the vacuum cleaner motor. Then, a short flexible hose, 3 ft. or so long, with a hand-held 'pistol' sort of nozzle on the business end, was connected to the heating element.
The details on this are quite fuzzy now as I've never actually seen one, only an illustration of it. But the thing that sticks out about it is the fact that it did have a heating element in it rather than just relying on the mild warmth that comes from the vacuum cleaner motor.
The 1920s Air-Way chief also had a hair-dryer bonnet that, if I recall correctly, was very similar to the Filter Queen setup. The instruction booklet suggested that the user place the motor "near a fireplace" so as to introduce heat into the air stream! Can you imagine?!