Carbon Monoxide is the result of incomplete combustion, and you'll find it on the exhaust side of all the appliances that I know of that burn hydrocarbons.
If you want to heat an area you need a heater with a separate combustion and hot air set up. The exhaust need to be vented in an area with good airflow.
If you are cooking, heating, lighting an enclosed area using hydrocarbons as fuel, which is highly inadvisable, you need to have a battery operated CO monitor.
Don't confuse a low Oxygen sensor with a CO monitor. CO can kill you way before the oxygen sensor turns the appliance off.
I know life is terminal, but please don't shorten it.