Coroner David Crerar was "not able to state unequivocally" that an Invercargill infant died as a result of overheating in 2010, but said it was a "risk factor" for premature deaths of vulnerable children.
Chesara Anna-Rose McMurdo, 18 months, was put to bed by her mother, Taryn Latchford, on September 28.
About 6.45am the next day, Ms Latchford found the toddler dead.
In his formal written findings, Mr Crerar said two infants had died in Invercargill within a week of each other, with the deaths having some similar circumstances. The homes of both children had heat pumps in operation when they died.
At the inquest, Constable Regan Price of Invercargill police said the temperature in Chesara's bedroom was "very warm - 20 to 25 degrees". The temperature panel on the heat pump remote read 28C.