A study of more than 2000 New Zealand children has found nearly half are sleeping in bedrooms that are too cold.
The pioneering study was a joint project between the building researchers BRANZ and the University of Auckland longitudinal study, Growing Up in New Zealand.
It got eight-year-olds to spend two days collecting temperature and humidity information at home and school.
The results made for sober reading, with about 1000 children going to sleep in bedrooms that were too cold - at or below 19C - with the temperature in some rooms dropping to under 4C by the morning.
A further 13 percent slept in rooms that were too hot or humid, with the hottest bedrooms reaching more than 34C.
University of Auckland Professor of Child Health Susan Morton said the best indoor temperature was between 19C and 25C.
Children living in poverty were more likely to live in houses with temperatures outside of that, and had poorer overall health.
"Those who were living in families experiencing more poverty, those who were likely to be in overcrowded situations," Morton said.
"With younger mums and with less support available to the family more generally."
Children experiencing temperatures outside the 19C-25C range are more likely to suffer conditions such as upper respiratory tract infections, asthma, ear infections and tonisilitis, Morton told Morning Report.
Arya Naidu, now 12 years old, took part in the research four years ago and said she was proud to be part of a study making a difference.
But she was disappointed some homes were not up to scratch.
"It's just really sad that some people don't have the right living conditions," Arya said.
"I believe that every child, every family, deserves to have a warm and dry home that they can just live in and be happy in."
BRANZ scientist Dr Chris Litten, from a research organisation that aims to improve New Zealand's building system, said New Zealand needed to do better with its housing stock standards.
"We need to build better houses, we need to insulate them and on top of that we need to be able to heat them properly and be able to afford to heat them."
Litten said good work was being done by the Ministry of Business, Innovation and Employment to look at improving energy efficiency in homes.
But he said housing standards were lagging behind the rest of the world, and it was time to catch up.