Mr Emms, 46, plundered a charity fund which had been set up for his son Michael Emms, the youngest person in Britain to be diagnosed with motor neurone disease.
Friends and family took part in sponsored events to raise £55,000 to send the teenager to China for pioneering stem cell treatment.
But a judge today said Emms had 'betrayed' the fundraisers by plundering the Michael Emms Trust Fund after the treatment failed. He was sentenced at Cardiff Crown Court after being found guilty of fraud at a previous hearing.
Judge Robert Britton told Emms: "This was a most despicable crime and there was a degree of cunning.
"You were in a position of trust and the victim was your son who was relying on this fund.
"But the emotional loss to Michael's friends and family was also huge and this was the greatest form of betrayal."
The judge said the money taken by father-of-three Emms has never been recovered.
Prosecutor Meirion Davies said: "A lot of work by a lot of good people had helped put money in that fund.
"What sort of man would trick his own son out of that money and use it for his own purposes?
"It was despicable - someone who could do something like that is beneath contempt."
Cardiff Crown Court heard Emms tricked Michael's grandmother Anne Brandon who was one of the four people authorised to sign the charity's cheques.
Mr Davies said: "Emms said he was booking a holiday to the USA for Michael and needed two cheques.
"One was for £3,000 for the holiday and the other was £300 for insurance.
"Mrs Brandon wrote the cheques out to a travel agency called Travelcare and signed them - but left them blank because Emms didn't know the exact amounts."
But the court heard Emms altered one of the cheques to get his hands on the £16,500.
The jury heard Mrs Brandon and her husband David had 'second thoughts' and asked for the cheques to be returned.
Mr Davies said: "Emms was upset that they were suspicious but they had every right to be. Emms went to their home and burned the cheques in front of them.
"It was theatrical and carefully calculated to hide the fact that one of them was a blank piece of paper."
The court was told Emms had already cashed one cheque for £16,500 after changing the payee to 'cash'.
Mr Davies said: "Police searched his home for the money but Emms told them: 'It is not here - I spent it.'
"He had carried out a cold-blooded and deliberate deception then lied to extricate himself from a deeper and deeper hole.'
The court heard Emms, of Beaufort, Ebbw Vale, South Wales, had a £15,000 business debt at the time the cheque was cashed.
Emms had broken up from his wife Theresa at the time he allegedly stole from the trust fund.
The family had to take out a loan to pay for Michael's funeral when he died in April last year.
Emms, who was found guilty of fraud at an earlier hearing, showed no emotion as he was led away to the cells.
Crown Prosecution spokesman David Watts said after the case: "Many people who gave to the fund will feel let down and angry to learn what happened to the money they contributed in good faith."