Hallmark was a brand of furnaces produced by Boyertown Furnace Company located in Boyertown, PA.  Frank Wilhelm originally manufactured the Hallmark Warm Air Furnace with the company he founded with his brothers in 1939, The Atlantic Heating and Cooling Company.   His company was purchased by Boyertown Furnace Company which relocated the production facilities to PA.  With this acquisition, Boyertown Furnace Company took over the production of the Hallmark brand in 1981.  Eventually, the Hallmark brand was phased out of production altogether.  No replacement part information is available.