Vent-free, propane-fueled space heaters are incredibly efficient. In fact, based on manufacturers’ data, they’re 99.9 percent efficient.

These heaters also include a smart-safety feature called an oxygen depletion sensor.
This device protects against the dangers of carbon monoxide by automatically turning
off the heater if oxygen levels drop below specified thresholds. Some models also offer thermostats and heat distribution blowers for more efficient operation. The right heat, right where you want it, without the cost of electric, or the hassle of installing a vent-pipe.