Cold Homes in New Zealand - Does Increasing the Heater Capacity Improve Indoor Temperatures?

Many houses in New Zealand are cold due to lack of insulation, low capacity heating systems (unflued gas heaters or small portable electric heaters are very common) and/or low heater use. This paper examines the effect of increasing the heater capacity on the indoor temperature in pre-80s houses with similar insulation levels. During the winter of 2006, room temperatures and heater use were measured in 36 houses in the Hutt Valley (New Zealand), as part of a larger intervention study examining the effects of heating on childhood asthma. Prior to this monitoring period, when it was physically possible, uninsulated houses received underfloor and ceiling insulation. Houses in an intervention group (n=21) received a higher capacity replacement heater (heat pump, wood pellet burner or flued gas heater), generally installed in the living room area, while the remaining houses in a control group (n=15) continued to use their original low capacity heater (mainly unflued gas heaters). The intervention group experienced a higher room temperature than the control group (17.8 C vs. 15.1 C in the living room, p<0.01; 16.3 C vs. 14.2 C in the bedroom, p=0.02). The indoor temperature increase in the intervention houses was mainly due to the higher capacity heater installed because no significant differences were found in the estimated hours of weekly heater use (p=0.24). Despite having the insulation upgrade and a higher capacity heater installed, in 52% of the intervention group living rooms and in 85% of the intervention group bedrooms, the temperature did not reach the level recommended by World Health Organisation. Therefore, it was apparent that user behaviour and socioeconomic circumstances, as well as structural features of the houses, are important determinants of indoor temperatures.