Hair dryer.
Air-Way offered this feature in 1920 on the first upright. That may be what the article's talking about. Electrolux also claimed it could be used as a hair dryer starting with the model X1. Eureka had a special hair drying tool on an early hand vac, in fact, that's one of the pictures used in the Vacuum of the day feature here.
Any vacuum with a hose would do if you hook the hose to the blower end and set it near an oven door. Actually, that's not nessecery, as the motor itself creates warm air, but Air-Way didn't think of that in 1920 when they put out the instruction book.