heater core hoses connection direction

dear all  the heater core  if I am looking from  
engine  side
(my car left side driver )
what hose is the hot water input  the  left of the car  
or the right side ?
what happens if connected in reverse does the
heater core blows up ?
is there an internal bypass valve inside the heater
core ?
and I read on the web the  service manual maybe
wrong (mention hot input is the left side of the car
)
I wish to get done help    it's winter and the hot air
intensity (not air pressure  blower fan motor is ok )
comming out is very weak.
note the heater core is not clogged and
the air flaps aren't punctured .
thank you in advance