Yes, it's an aftermarket heater. It may have been installed by the dealer or even purchased from Western Auto and installed by the owner.

I have a recirculating heater. It has a shutoff valve on one of the heater hoses near the water pump to keep hot water from entering the heater core in the summer.

I never bother turning it off because it doesn't really heat up the cabin with the fan off and I drive with the windows down and intake vents open anyway.

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)