Oxygen Deprivation is a problem for units that are inside a room and have atmospheric burners.
Oxygen deprivation occurs when insufficient air is available for the burners to burn because of lack of enough fresh air ventilation.
This happens when plaster vents are rendered over and existing vents are removed. Signs of oxygen deprivation are yellow flames, sooting or front venting of flame seeking air.
It can be as dangerous as carbon monoxide (CO) as it can progress to allowing CO into the room as it draws air down the flue and then flues CO into the room.
Overcoming the problem
To overcome the possibility of oxygen deprivation when considering new products, balanced flue (sealed room) wall furnaces and space heaters are safer as they draw oxygen from the outside and do not burn the room air because they have air drawn from outside into the combustion chamber. The additional benefits of these units are they are more efficient than atmospheric burner type units. They still require 2 year services and carbon monoxide testing.