David Johnson, 56, of Ipswich, Suffolk, was found guilty of manslaughter last month following a two-week trial at Norwich Crown Court.
Robert Schenker, 31, of Peterborough, Cambridgeshire, died of carbon monoxide poisoning after Johnson blocked the flue leading from his kitchen boiler while rebuilding a chimney, jurors were told.
Prosecutors said Johnson had been "grossly negligent".
He had allowed mortar to drop and drip into the chimney and the mortar had solidified, preventing carbon monoxide from escaping into the atmosphere. The gas had leaked into Mr Schenker's house and killed him, the court heard.
Mr Schenker, who ran a business selling spare parts for Porsche cars, was found dead in bed in March 2006 - three days after Johnson started work, jurors heard.
Johnson, who lived in Peterborough when Mr Schenker died but now lives on a boat in a marina at Ipswich, had denied manslaughter.
Alastair Malcolm QC, mitigating, said there was no evidence Johnson was a "cowboy builder" but added his work had fallen "below his usual standards" on this occasion.
Sentencing today at Norwich Crown Court, judge Peter Jacobs said: "You deliberately and knowingly exposed someone to a high likelihood of death through carbon monoxide poisoning."