Health: Our homes too cold in winter and too warm in summer

In New Zealand, houses are not always at safe and comfortable temperatures.

A third of New Zealand homes are too cold in winter, and over a third are too warm in summer, according to Stats NZ.

As part of the year-long 2018 General Social Survey (GSS) survey, Stats NZ took temperature measurements in 6700 homes.

“This is the largest-scale temperature measurement carried out in New Zealand to date and represents a snapshot at the time of each GSS interview,” wellbeing and housing statistics manager Dr Claire Bretherton said.

The average (mean) temperature recorded inside homes during a GSS interview was 21.4 deg C. Temperatures in winter, however, were colder at 19 deg C. In contrast, the average temperature recorded in summer was 23.9 deg C. Indoor temperatures recorded during the survey ranged from near freezing in a small number of homes to over 30 deg C in others.

“Most temperatures were recorded between late morning and late afternoon,” Dr Bretherton said.

“We measured temperatures where the interview took place, likely to be in a living room or kitchen, which are more commonly heated than bedrooms or other parts of the home.”

Housing in Southland was significantly cooler than the national average in summer (with a mean recorded temperature of 21.6 deg C), while Gisborne/Hawke’s Bay and Bay of Plenty, averaged over 25 deg C.

The Household Energy End-Use Project, a study by the Building Research Association of New Zealand, rated 20–25 deg C as a comfortable indoor temperature. Of all summer temperatures recorded by the GSS, 36 percent were 25 deg C or more.

“These high temperatures can make people uncomfortable,” Dr Bretherton said.

“However, of most concern is that in around a third of homes the recorded temperature in winter was under 18 degrees, which is below the World Health Organization’s minimum healthy indoor temperature.”

Lower recorded temperatures were also associated with other signs of cold. For people living in homes where the recorded temperature was lower than 16 deg C, 45 percent said they could see their breath inside during winter, and 36 percent rated their house as always or often cold.

“If the indoor temperature is 16 degrees or less, some people might need at least two or three layers of clothing, adding a singlet or a jersey to keep warm, if not both,” Dr Bretherton said.

“That’s especially so for the very young and very old.”

People living in houses they didn’t own, and those who said they didn’t have enough money for everyday needs, also experienced colder indoor temperatures in winter (with mean recorded temperatures of 18.1 and 17.7 deg C, respectively). Houses with efficient heat sources such as wood burners and heat pumps recorded warmer average temperatures in winter than houses with electric heaters, or where people did not heat regularly.

Household expenditure data from the Household Economic Survey 2015/16 showed more than one-quarter of New Zealand households had at least one indicator of energy hardship – such as struggling to pay utility bills on time, having cold, damp, or mouldy housing, or paying more than twice the median for energy costs as a proportion of household income. At the extreme end, around 1 in 4 low-income households paid more than 10 percent of their income on household energy costs.

Why did Stats NZ want to do this?

In New Zealand, houses are not always at safe and comfortable temperatures, but the extent of this problem is not known.

Measuring temperatures in homes selected for the GSS allowed Stats NZ to do this across many different groups. He Kainga Oranga, University of Otago’s Housing and Health Research Programme, supplied the thermometers and gave advice on the process.