I am not a healthcare expert, but I've traveled the world over and seen many sad living conditions. I fear that you will not be able to find any data for which the only possible cause of detrimental health impacts (e.g., birth defects or pre-term births) is unsafe (e.g., kerosene or smudge pot or garbage) heaters. Where people resort to such equipment, there are other serious problems (contaminated water supply, unsafe ambient air, inappropriate building and insulation materials, lack of proper nutrition, no immunization, etc.).