A study of more than 2000 eight year-olds has found nearly half are sleeping in bedrooms that are too cold.
The world-first research 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 acting as " at-home scientists" to spend two days collecting temperature and humidity information at home and school.
Growing Up in New Zealand spokesperson Professor Susan Morton says the research is ground-breaking.
She spoke to Susie Ferguson.