Propane heaters can be used indoors, but it is important to use them safely and only in well-ventilated areas. Unvented, or vent-free, propane heaters are not recommended for use indoors because they can produce dangerous levels of carbon monoxide if not used properly. Vented propane heaters can be used indoors if they are installed and used according to the manufacturer’s instructions and local building codes. In general, it is best to use propane heaters only when necessary and for short periods of time, and to make sure that the area is well-ventilated to prevent the build-up of harmful byproducts. It is also important to regularly maintain and inspect your propane heater to ensure that it is working properly and safely.