A Chelmsford man who won $1 million from the Massachusetts State Lottery in 2009 will serve at least 18 months behind bars after he admitted to swindling more than $21,000 from his home oil company’s customers, according to Middlesex District Attorney Gerry Leone.

Michael Santaniello, 60, of Chelmsford, pleaded guilty in Lowell District Court last week to stealing money from more than a dozen of his clients, many of whom are elderly, by collecting deposits for service or repairs to home oil tanks and burners that he never completed, Leone said in a statement. Santaniello owns Mike’s Oil Heat Service in Chelmsford.