Propane- and kerosene-fueled heaters are prodigious heat producers. But because of their open flames, the risk of carbon-monoxide poisoning, and the hazard associated with handling the fuel, it's best not to use fuel heaters indoors, except in areas with good ventilation.
We tested two propane fuel heater models and two that use kerosene. None fared well in our safety tests and all produced a small but measurable level of CO and emitted particulates, though not enough to be a serious hazard. The propane fuel heater models have a low-oxygen shutoff valve; the kerosene heaters a tip-over switch.
Still, these fuel heaters can be useful. During a winter power outage, you might use one to keep water pipes in an uninsulated basement from freezing, for example.
Before you operate a fuel heater, contact your building department about usage restrictions. Never move a fuel heater while it's in use, and regularly clean and inspect it. During a power outage, place the heater in the center of a well-vented room that has battery-powered carbon-monoxide and smoke alarms. Monitor the fuel heater continually, and turn it off when you go out or to bed.