New Zealand homes are noticeably warmer than they were two decades ago, but the rooms people sleep in are still running cold, according to a major new study of how the country heats its houses through winter.
The Building Research Association of New Zealand monitored temperatures and energy use in about 260 homes between 2022 and 2025 for its HEEP-2 study, an update on similar research carried out in the early 2000s. The headline finding is encouraging. Average indoor winter temperatures have climbed by somewhere between 2.6 and 3.5 degrees since the first study, and living rooms now sit comfortably inside the range health experts recommend.
Living rooms averaged 20.4 degrees between 5pm and 11pm, the part of the evening when families are most likely to be home and awake. That is well above the World Health Organisation minimum of 18 degrees for a healthy home. BRANZ senior research scientist Vicki White said the gains were real. “Living rooms are now typically reaching 20.4°C in the evening, comfortably above the World Health Organisation’s recommended minimum of 18°C,” she said.
A big part of that change is the heat pump. In the early 2000s only around one in a hundred households had one. Today more than 60 percent of New Zealand homes are heated by a heat pump, a shift that has quietly rewritten the way the country stays warm.
The problem is what happens once people go to bed. Bedrooms averaged just 16.5 degrees overnight, and the study found that more than 40 percent of overnight winter bedroom readings fell below 16 degrees. One in four bedrooms had dropped below 14 degrees by 6am. Helen Viggers, a senior research fellow at the University of Otago, summed up the pattern bluntly. “Despite the 3°C improvement and the relatively affluent households sampled, over 40% of the overnight winter bedroom temperatures were below 16°C,” she said, noting the contrast with the warmer living rooms down the hall.
The reason is simple enough. Most people are not heating the rooms they sleep in. Priscila Besen, a senior lecturer at Auckland University of Technology, pointed to the figures that matter most for families. “41% of households never heat bedrooms, and 31% report never heating bedrooms used by children under 5,” she said. The study found a similar gap for older children, with around 42 percent of school-aged children’s bedrooms never heated.
That gap matters because cold bedrooms are not just uncomfortable, they carry a health cost. Dr Lucy Telfar-Barnard, a healthy housing researcher at the University of Otago, said sustained cold takes a toll on the lungs. “When it’s consistently cold, then our lungs get inflamed,” she said, leaving people more open to infection and more likely to have asthma triggered. Cold and damp indoor air has long been linked in New Zealand research to higher rates of respiratory illness and winter hospital admissions, particularly among young children and older people.
Dr Nigel Isaacs, a building scientist at Victoria University of Wellington, said the overall direction was good but the night-time picture had not caught up. “Overnight bedroom temperatures are still too often below healthy levels,” he said.
The study also captured how cold many homes still feel to the people living in them. In an accompanying survey, 48 percent of households said their home felt colder than they would like at least some of the time, and 20 percent said they could occasionally see their own breath indoors during winter. Three-quarters reported condensation on windows or walls over winter, and around a third reported damp. These are the everyday signs of a house that struggles to hold its heat, and they remain common despite the warmer living rooms.
There is a flip side that is starting to show up in newer houses. About 20 percent of households said their home got uncomfortably warm in summer, and a quarter of bedrooms averaged 24 degrees overnight, a level that points to a growing risk of overheating in well-sealed modern builds. As New Zealand keeps lifting insulation standards, designers will increasingly have to balance keeping winter warmth in against letting summer heat out.
What ties the findings together is access. BRANZ framed the result as an interaction between the ability to heat a room affordably, the quality of the heating system, and how well the building itself holds warmth. A well-insulated home with an efficient heat pump and an affordable power bill can comfortably clear the healthy range. A poorly insulated rental with an expensive plug-in heater often cannot, no matter how much the household wants to be warm.
That is where the policy question sits. Sam Archer of the New Zealand Green Building Council noted that the Warmer Kiwi Homes programme, which subsidises insulation and heating for lower-income households, has been running at around 80 to 100 million dollars a year but faces an uncertain future beyond June 2027. The HEEP-2 results suggest the scheme and the rules behind it have helped move the national average in the right direction, while leaving the coldest rooms in the house as the next job to finish.
For now the takeaway for most households is practical. Living rooms are winning the battle against winter. Bedrooms, where New Zealanders spend roughly a third of their lives, are still the cold spot worth fixing.
You can read the original coverage at RNZ and the full expert reaction collected by the Science Media Centre, drawing on research from BRANZ.
How warm do you keep your bedroom in winter, and have you found a heating set-up that works without blowing the power bill? Share your tips in the comments below.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job 🙂
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