How to set time zone permanently - Mailing list pgsql-admin

How do you set the time zone permanently in postgresql?
I can use the set time zone 'EST'  in psql on template1
show time zone & it shows EST
exit
then go back into psql & do a show time zone & it says time zone unknown

Where do I & how do I permanently set the time zone?

thanks
Pam Wamper