The equity up for sale is priced at 100,000 levs ($66,000/51,000 euro), the municipality of Shumen said in a statement published on its website.
The tender winner will be obliged to resume the supply of heating energy for the 2013-2014 season.
Bulgaria has already sold the heating utility companies in most of its big cities in an attempt to further liberalise its energy market after joining the European Union on January 1, 2007.
(1 euro = 1.95583 Bulgarian levs)