-- Last Updated: Feb-08-13 12:25 AM EST --
...... any potential for LP gas (propane) burners , appliances , etc. to emmit carbon dioxide in levels that are above the safe levels , is due to the unit burning extremely inefficiently due to lack of proper oxygen levels being available to the combustion mixture .
Also improper gas pressure to the appliance can be the cause of this . To much pressure and to much gas is released at the combustion point , and not enough oxygen to support burning that much gas ... the result , inefficient gas burn (incomplete gas burn) ... the exhaust has to high of concentrations of , CO2 - NO2 - CO - water vapor .
This can be caused by fouled orfices . Fouled orfices (fouled with carbon build up) that happened because there was not enough oxygen in the combustion mix .
The way it can happen that there becomes not enough oxygen is that the oxygen in the closed area that the unit is burning in has become depleated because the burning unit has used it up already . Therefore , it is important to be certain there is sufficient "fresh air" allowed into the closed burning area (ie, a vent to outside or cracked open window , etc.) .
This is why they tell you to not use your gas range as a heater inside your home . The assumption is that if using the range as a heater , you will be doing so for long periods of time such as full or part days , many hours in a closed space (the home) . This has the ability to use up the available oxygen and thus causing the range to burn terribly inefficiently , which in turn can cause the carbon build up on orfices , and combustion exhust byproduct to emmit higher than safe levels of carbon monoxide .
The same would hold true with an LP gas space heater . Therefore it is recommended that if one choses an "unvented" LP heater , one should be certain an "Oxygen Depletion Sensor" (ODS) "safty cut off" feature is part of the heaters make up .
When it comes to the carbon monoxide issue of the various fuel types of available space heaters that are not "externally" fresh air vented nor chimney exhausted ... LP gas is the safest by far .
The water or condensation issue from burning fossil fuels is due to the byproduct of burning hydrogen ... ie, water . In dry winter air , sometimes the added moisture into the air can be a benifit . If the space the heater is heating already has high humidity levels then the result will most likely be condensation on things .
The most important thing to remember when using a non vented space heater , natural gas , LP gas , kerosene , other ... is be certain you have a fresh air exchange taking place in the area the heater is heating .
And in all cases it is recommended to have a carbon monoxide (CO) alert sensor installed in the operating area ... just be safe .