| The high amounts of nitrogen oxides seem to be attributed to unvented heaters. |
| Carbon dioxide is released through livestock respiration and manure decomposition, and by unvented heaters. |
| Because they are unvented and not permanently installed, these portable heaters are potentially more hazardous than options listed earlier. |
| Install the plastic ground cover as described above for an unvented crawl space. |
| For example, he said, carbon monoxide can be created by unvented appliances like gas stoves, ovens and clothes dryers. |
| Throughout the world, nearly one billion people burn coal for heating and cooking in unvented ovens. |
