When using a propane heater, you need to make sure that the room is properly ventilated. This is because propane heaters produce carbon monoxide gas, which can be dangerous if it builds up in an enclosed space. The best way to ventilate a room when using a propane heater is to open a window or door slightly, so that fresh air can circulate. You should also avoid using the heater in small, enclosed spaces such as tents or RVs. If you do use the heater in an enclosed space, be sure to monitor the level of carbon monoxide carefully and evacuate the area if it starts to build up.