Granted Patent
Utility
US 3,940,837 · App. 05/495,990
Hot air furnace with improved heat exchanger construction
Inventor:
John Wiese
Patented Case
View Patent ↗
Granted: Mar 2, 1976
Filed: Aug 9, 1974
Inventor
John Wiese
Assignee (at issue)
The Singer Company Limited
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.