Andrew McGowan, 33, of Great Yarmouth, bled to death in a flat in Dickens Court on 14 November from stab wounds.
Warren Ricardo Blake, 18, of Thorncliffe Road, south London, was found guilty of his murder.
Judge Stephen Holt, sentencing at Norwich Crown Court, said it was clear Blake had armed himself with a knife.
The case of Tevin Birmingham, 21, of Spring Road, Ipswich, who was convicted of manslaughter, was adjourned for sentencing to 1 September.
The court heard Blake and Birmingham, who were drug dealers, agreed to meet Mr McGowan at the Great Yarmouth flat to sell Class A drugs.
Mr McGowan, who was drunk, had taken drugs and was generally in a poor physical state, the jury heard.
It was said that he went to the flat armed with a claw hammer, either to confront the dealers about the sale of drugs to his girlfriend or to rob them.
In the confrontation that followed Blake stabbed Mr McGowan five times, piercing his heart and leading him to bleed to death.
Judge Holt told Blake: "In my view you had provided a weapon to deal with such a situation. I accept you had no plan to deal with this, but you attacked this man with a combat knife and the jury has dismissed your defence of self-defence.
"You stabbed McGowan and let him bleed on the landing with no attempt to call the emergency services."
Philippa McAtasney QC, on behalf of Blake, said Blake was "still a young man and distraught by the verdict".
"He (Blake) would never have been involved in this incident if McGowan had not gone to the premises and... was provoked and taken by surprise," said Ms McAtasney.
She said Blake, who had been abandoned by his family, had never been in trouble for knife crime and was "not at the top of the tree as a drug dealer".
A teenage drug dealer has been told he will serve a minimum of 17 years for the murder of a father stabbed to death in a seaside town.