Granted Patent
Utility
US 4,386,500 · App. 06/249,825
Water heater heat exchange apparatus, kit, and method of installation
Inventor:
Boyd Sigafoose
Patented Case
View Patent ↗
Granted: Jun 7, 1983
Filed: Apr 1, 1981
Inventor
Boyd Sigafoose
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.