A Taupō house fire that claimed the lives of three people including an infant was started by the infant's father, according to a coroner's report.

On Tuesday coroner Wallace Bain released his findings on the March 17, 2017, Taupō house fire that claimed the lives of four-month-old Ash David Millar, his mother Katie Rose Bruce, 20, and the man responsible, Scott Dustin Millar, 26.

It has been almost one year since the fatal 3am fire which gutted the house on the Napier-Taupō highway, about 40 kilometres east of Taupō.

Millar initially survived and was flown to Waikato Hospital in critical condition but died as a result of his injuries.

In his findings, Bain found a scenario put before him by the police fitted with the evidence.

Police believed Millar intended to cause the death of Bruce, Ash and himself.

"Police say the mere fact he poured petrol and ignited the fire in such a close proximity to baby Ash is reckless and ultimately concludes that he is also responsible for the death of Ash and himself," he wrote.

"The evidence does not, however, establish sufficiently an element of intent for him and Ash.

"The court agrees with the second scenario, after having reviewed all the available evidence, that Scott Millar intended to cause the death of Katie Bruce, but not himself and Ash."

-Stuff.co.nz