Parents have been warned to check their heat pump temperatures as the devices were cited in the deaths of two babies.
Separate inquests were held for Chesara Anna-Rose McMurdo, 18 months, and Joseph James Batchelor-Smith, 9 months, in Invercargill yesterday. They died in separate incidents within a week of each other in 2010.
Otago-Southland Coroner David Crerar said their deaths highlighted risks associated with overheating in vulnerable children.
The inquests heard the temperatures in the children's rooms were about 25C - considered the maximum a child could sleep in.
Chesara's mother, Taryn Latchford, told the inquest she had put her daughter to bed about 7.30pm wearing a nappy, a stretch and grow and pyjamas.
The house had a heat pump fitted, usually set between 18C and 24C.
About 6.45am when Mrs Latchford checked on Chesara she could see her face was blue. She was pronounced dead soon after an ambulance and medical staff arrived. Ms Latchford said her daughter had been happy and healthy in the days leading up to her death.
Statements noted some felt Chesara's room was very warm and Constable Regan Price, of Invercargill, said the heat pump remote showed a setting of 28C, estimating the temperature in Chesara's room to be about 25C.
Professor Barry Taylor, a sudden infant death syndrome researcher of the University of Otago, said that temperature would be the maximum a child would be able to sleep in - any warmer and a child's body temperature would increase to dangerous levels.
In his verbal findings, Mr Crerar found Chesara's cause of death was unexplained sudden unexpected death in infancy.
He found Joseph died from septicaemia and a fever exacerbated by overheating in his sleeping environment, from a heat pump.
Joseph's mother Georgina Daisley (nee Smith) said Joseph had been born premature following an emergency caesarean section.
On the night of his death, Mrs Daisley left Joseph - healthy except for a runny nose - in the care of housemate Honey Samson.
Ms Samson said the heat pump had been set on 25C and, after feeding Joseph and his 2-year-old sister dinner she put Joseph back to bed. She went to bed about 10pm. Ms Samson got up about noon to change the elder child's nappy but "just left Joseph because he was asleep".
Mrs Daisley came home and went to get Joseph about 2.30pm. "When I went to his cot I saw he was dead. He had foam coming from his mouth and nose." Ambulance officers responded, with one remarking on the heat inside the house.
Professor Taylor said parents had to be more careful with infants, who were unable to self-regulate their temperatures.
"In terms of assessing a baby, put your hand behind the neck and feel what the core temperature is there, and then feel the hands and feet. "They should be slightly cooler. If the hands and feet are as hot, it means [they're] trying to get rid of heat."