I also do not know; however, I think that the codes on Harrison radiators and heaters were not the date they were installed or manufactured.
It might have been the date of the first year of that style heater/radiator?
However, Lonnie's 1954 heater would have been a style also used in 1953 (maybe the color was different in 1953)?
I'll check some of the 53-55 fresh-air/air-flow heaters that I have. Lonnie, where on the heater-case did you find that first code?
