Research | Children’s Health Respiratory Health Effects of Exposure to Low-NOx Gas Heaters in the Classroom: A Double-Blind, Cluster-Randomized, Crossover Study Unflued Guy B. Marks,1,2,3 Wafaa Ezz,1,2 Nathan Aust,4 Brett G Toelle,1,2 Wei Xuan,1 Elena Belousova,1 Carmen Cosgrove,4 Bin Jalaludin,3 and Wayne T. Smith 2,4,5 1Woolcock Institute of Medical Research, Sydney, New South Wales, Australia; 2University of Sydney, New South Wales, Australia; 3University of New South Wales, Sydney, New South Wales, Australia; 4Environmental Health Branch, New South Wales Health Department, New South Wales, Australia; 5University of Newcastle, Newcastle, New South Wales, Australia children’s health has not been assessed. Bdnuorgkca : There are long-standing concerns about adverse effects of gas appliances on respiratory health. However, the potential adverse effect of low-NOx (nitrogen oxide) unflued gas heaters on ers in school classrooms. o Bjectivs : Our goal was to compare the respiratory health effects and air quality consequences of exposure to low-NOx unflued gas heaters with exposure to non–indoor-air-emitting flued gas heat- Methods : We conducted a double-blind, cluster-randomized, crossover study in 400 primary school students attending 22 schools in New South Wales, Australia. Children measured their lung function and recorded symptoms and medication use twice daily. Nitrogen dioxide (NO2) and formaldehyde concentrations were measured in classrooms using passive diffusion badges. r esult : NO2 concentrations were, on average, 1.8 times higher [95% confidence interval (CI), 1.6–2.1] and formaldehyde concentrations were, on average, 9.4 ppb higher (95% CI, 5.7–13.1) dur- ing exposure to unflued gas versus flued gas heaters. Exposure to the unflued gas heaters was associ- ated with increased cough reported in the evening [odds ratio (OR) = 1.16; 95% CI, 1.01–1.34] and wheeze reported in the morning (OR = 1.38; 95% CI, 1.04–1.83). hTe association with wheeze was greater in atopic subjects. hTere was no evidence of an adverse effect on lung function. c onclusion : We conclude that classroom exposure to low-NOx unflued gas heaters causes increased respiratory symptoms, particularly in atopic children, but is not associated with significant decrements in lung function. It is important to seek alternative sources of heating that do not have adverse effects on health. k ey words 27 July 2010] : children, nitrogen dioxide, randomized controlled trial, respiratory health effects, schools. Environ Health Perspect 118:1476–1482 (2010). doi:10.1289/ehp.1002186 [Online There has been long-standing concern about the health consequences of indoor exposure to gas combustion products (e.g., Garrett et al. 1998; Jarvis et al. 1996, 1998; Kerkhof et al. 1999; Melia et al. 1979; Ng et al. 2001; Phoa et al. 2004; Pilotto et al. 1997; Ponsonby et al. 2001a; Wong et al. 2004). Most con- cern has focused on the respiratory effects of emissions of oxides of nitrogen, particularly nitrogen dioxide (NO2) (Bauer et al. 1986; Chauhan et al. 2003; Tunnicliffe et al. 1994), although not all studies have demonstrated adverse effects at the observed concentrations (Salome et al. 1996; Samet et al. 1993). There have been two randomized con- trolled trials that contribute a higher level of evidence. One of these is a parallel-group, randomized, controlled trial of a home- heating intervention conducted in a cohort of New Zealand houses that were poorly heated, including 55% with unflued gas heaters and others with electric or other heating sources, and in which at least one child had asthma (Howden-Chapman et al. 2008). Children whose homes were insulated and fitted with an effective nonpolluting heater had less noc- turnal cough and wheeze, fewer lower respira- tory tract symptoms, and better self-assessed health status during winter than those in the 1476 control group who did not receive any inter- vention until the study was over. There was no difference in lung function. This study demonstrated an improvement in clinically relevant health outcomes attributable to this home modification intervention. However, it is not clear whether the change was due to the nature of the fuel source or the effectiveness of the heating. Although the active group had substantially lower NO2 concentrations in the living room (8.5 µg/m3 vs. 15.7 µg/m3, p < 0.001) and in the child’s bedroom (means 7.3 µg/m3 vs. 10.9 µg/m3, p < 0.001) than the control group, there was also a 0.57°C higher average temperature in the child’s bed- room and a 50% reduction in the proportion of nights in which the temperature fell below 10°C in the active intervention houses. One limitation of the study was the absence of any blinding, which would not have been feasible in a parallel-group study. Because the outcomes that changed were all subjective, this possible source of reporting bias needs to be considered. However, despite these limita- tions, this study does strongly support the conclusion that there will be health benefits for children with asthma from the use of non- polluting, effective domestic heating sources in cold climates. The other randomized controlled trial was conducted in Australian schools (Pilotto et al. 2004). It was also a parallel-group, random- ized, controlled trial in which there was no attempt to blind participants in the active intervention group that they were receiving new heaters. The control classrooms were heated with unflued heaters. Among children with asthma in the randomized classrooms, those in the active intervention classrooms were less likely to report difficulty in breath- ing (during the day or night), chest tightness (during the day), and asthma attacks during the day. There was no difference in lung func- tion or airway hyperresponsiveness. As with the New Zealand study, the parallel-group design, which did not allow blinding, leaves some concern about possible reporting bias for subjective outcomes. In New South Wales (NSW), unflued gas heaters have been the principal form of heating used in schools for many years. In response to emerging concerns in the late 1980s, the NSW Department of Education embarked on program of replacing its existing older-style unflued gas heaters with a newly designed low-NOx (nitrogen oxides) unflued gas heater (Bowin Lo-NOx; Bowin mfg Pty Ltd, Sydney, Australia) (McPhail et al. 1989). These are designed to conform to a 2-ng NO2 per J standard (Bowin mfg Pty Ltd). However, there are continuing concerns about potential hazards arising from these heaters. There has been one published report of a laboratory-based assessment of emissions from low-NOx unflued gas heaters (Brown et al. Address correspondence to G.B. Marks, Respiratory and Environmental Epidemiology, Woolcock Institute of Medical Research, P.O. Box M77, Missenden Rd. PO, Sydney NSW 2050, Australia. Telephone: 61 2 9114 0466. Fax: 61 2 9114 0014. E-mail: guy.marks@sydney.edu.au Supplemental Material is available online (doi:10.1289/ehp.1002186 via http://dx.doi.org/). We acknowledge the assistance of the New South Wales Department of Public Works and Bowin mfg Pty Ltd (Sydney, Australia) in designing and imple- menting the installation and operation of the flued and unflued gas heaters. We acknowledge technical assistance from A. Quinones and P. Kidd. This study was funded by the New South Wales Department of Education and Training, who facili- tated its implementation. The authors declare they have no actual or potential competing financial interests. Received 18 March 2010; accepted 20 July 2010. ovlume 118 | number 10 | October 2010 • Environmental Health Perspectives