It is generally not safe to use a propane heater indoors. Propane heaters produce carbon monoxide, which is a colorless and odorless gas that can be deadly if inhaled. In a confined space like a home, the levels of carbon monoxide can build up quickly and become dangerous. Additionally, propane heaters can be a fire hazard if they are not properly vented or if they are placed near flammable materials. It is best to avoid using a propane heater indoors and instead use a safe alternative, such as an electric heater.