Invented in the early 1920’s they were a solution to space heating separate rooms. Back in the day most furnaces had a main boiler in the basement with steam pipes routed to all the radiators. During the spring or fall that became wasteful because of all the effort needed to get the boiler up to temperature for maybe one day and then put it out. The Clow heaters were a furnace unto themselves that would allow the heating of a space without needing to crank up the main boiler. If you look in the background of Seinfeld’s apartment on his show, you will see a Clow.
Nowadays they are more of a novelty if they work at all.