Respiratory health effects of exposure to low-NOx unflued gas heaters in the classroom: a double-blind, cluster-randomized, crossover study.

Background: 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 children's health has not been assessed.

Objectives: 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 heaters in school classrooms.