How warm are our houses?

A few cold days in recent months prompted a question around what the usual temperature of a New Zealand home actually was, and if there was any data to use to answer this question. In short, how warm is the average home? Turns out the answer is 21.4°C.

Given the important focus on housing-related outcomes across New Zealand, and the various questions we sometimes field about various aspects of homes, we thought we would dedicated our Chart of the Month to recording what we know about average temperatures of houses across New Zealand.

As part of the 2018 General Social Survey (GSS), Stats NZ undertook measurement of the average temperatures of New Zealand houses, with support from Ministry of Housing and Urban Development, BRANZ, and He Kainga Oranga, University of Otago’s Housing and Health Research Programme. The 2018 GSS had a sample size of around 8,000.

The temperature taken was inside the house of a survey participant, if they agreed to this measurement being taken (93% did agree), and was taken in the room where the interview took place (presumably most often a living room, or office/study). Stats NZ notes that most interviews took place between late morning and late afternoon, with the average start time for the interview being at 2:19pm, meaning that temperature readings are most representative of daytime living area temperatures.

The average temperature across the year was 21.4°C, with an absolute sampling error of +/- 0.1°C.

Waikato region had the warmest houses recorded in the analysis, with an average temperature of 22.1°C, around 0.7°C higher than the national average. Auckland was also relatively warmer, at 21.9°C on average across the year.

Unsurprisingly, the south of the South Island recorded the coldest average house temperatures, with both Otago and Southland recording an average temperature of 20.2°C.

Less expected, but unfortunately as understandable, was the low average temperature recorded in Wellington region, at 20.6°C, 0.8°C lower than the national average. The lower temperature reading for Wellington aligns with previous Infometrics analysis showing Wellington houses were more likely to be unheated, mouldy, and damp.

The lack of heating in Northland and Auckland was quite striking in our earlier analysis but aren’t as clear to see in these average temperature readings. There are various reasons for this, but we expect a combination of different times of the year being surveyed and a generally warmer climate in Northland and Auckland relative to Wellington likely exacerbate the colder outcome for Wellington.

Funnily enough, houses are hotter in summer and colder in winter. Average house temperatures during summer were 23.9°C, falling back to 21.8°C in autumn and 20.7°C in spring, then down to 19.0°C in winter.

Those findings are all understandable. But the summer and winter temperature distributions do raise some concerns about how well some households can regulate the heat (and cold) throughout the year.

Throughout spring, summer, and spring, the majority of New Zealand households have an average temperature of 20-25°C. But in winter, only 37% of houses had an average temperature in this range, with a third of houses (33%) recording an average temperature of below 18°C. Another 28% of houses were 18-20°C, and a small proportion (2.1%) were over 25°C.

The greater distribution of temperatures in winter, that are much more skewed to colder temperatures, reinforces the challenges some households faced with the cold, including poor or no heating options, or draughts, dampness, and other difficulties. The World Health Organization defines healthy indoor housing temperatures as between 18-24°C.

While winters can be colder for a number of households, summers can become too hot for some households too. More than half of houses in summer had an average temperature of 20-25°C, but more than a third (36%) were over 25°C. Overheating has been identified a number of times recently in some parts of New Zealand.

My thanks to Jason Attwell, Nicolette Edgar, Rosemary Goodyear, and Abby Johnson for their assistance with receiving additional information about the regional and average season breakdowns of the temperature readings.