Natural Gas and propane are two of the safest gases to use in the home. A properly working propane or natural gas heater doesn't produce Carbon Monoxide is large enough quantity to even be rated. However with that said improper combustion of anything from paper to vet fuel will produces CO (Carbon Monoxide)..So the choice is yours I've used those heaters for the past three years with no problem, Just crack a window to allow air exchange and your good to go.