Paul Brian Edward Connelly appeals against 20-year sentence for trying to kill sons in Burnie car fire

A Tasmanian man is appealing his 20-year prison sentence for trying to kill his two children in a car fire, with his lawyer arguing his non-parole period exceeds that of some convicted murderers.

Paul Brian Edward Connelly, aged in his 50s, was found guilty of two counts of attempted murder after lighting two gas cylinders inside the family car while he and his two young sons were inside in late 2012.

They all escaped, but suffered serious burns.

Chief Justice Alan Blow had sentenced Connelly to 20 years in prison, with a non-parole period of 15 years, finding Connelly had decided to kill the boys to spite his wife, who had recently left him.

In the Supreme Court in Hobart today, Connelly appeared to wipe away tears as his lawyer Tamara Jago argued his appeal.

Ms Jago told the court the sentence, particularly with its non-parole period, was disproportionate to Connelly's offending, and demonstrated error.

She said the sentence was five years harsher than any other sentence imposed in Tasmania for crimes of that nature, and had a much harsher non-parole period.

"Here, the head sentence, if not excessive, must be considered at the very least to be an exceptionally heavy one," Ms Jago told the court.

Ms Jago said the non-parole period made the sentence manifestly excessive.

"The period that (Connelly) will have to serve in jail exceeds a large number of non-parole periods that are associated with convictions for the crime of murder," Ms Jago said.

Ms Jago told the court that prior to Connelly's sentence, the harshest sentence imposed for the crime was that of Patrick Burling, who received a 15-year prison sentence with a non-parole period of 10 years, for shooting a police officer.

Sentence not excessive: crown prosecutor

Crown prosecutor Darryl Coates told the court the sentence handed down by Chief Justice Blow was not outside the range of permissible sentences for the case.

"This was premeditated, to cause death to two young children ... and to take revenge on someone else," Mr Coates told the court.

"Given the facts of the case, the purpose of punishment, retribution ... tied into the fact his Honour found the accused was not remorseful, a sentence of non-parole of 15 years was not excessive."

Mr Coates said Connelly's actions also had the potential to harm other residents and caused a number of them to risk serious injury when they came to assist.

Mr Coates said when it came to Ms Jago's argument about murder sentences, the actual category of the offence was not important.

He told the court in some cases of murder the actual moral culpability of the offender would be very small compared to Connelly's case.

Judges Shan Tennent, Stephen Escort and Helen Wood have reserved their decision.