Never use your Blackstone Griddle within 36 inches of anything flammable. This includes walls, fences, trees, and roofs. Don't store any flammable materials near the iron, such as toys, backyard decorations, and plants. Yes, you can leave the iron outside.
Keeping it outside is the only option most people have because of the limited space in the house. In general, the recommended distance is 10 feet away from the house. However, this may vary depending on the type of iron you use and local regulations. Blackstone irons and other flat surface grills can be used on open porches as long as they are kept away from the house and from any flammable object.
The answer to this question depends largely on your specific grill and what your grill brand guidelines say. It is generally not recommended to use a Blackstone iron or any other gas or charcoal grill on an enclosed porch, as ventilation is very low and the danger of carbon monoxide poisoning, which can be fatal. There are several reasons why you should make sure you keep a hot grill at a safe distance from your home when grilling. You should also not use the grill under garages, awnings, or covered areas, unless there is at least 8 feet of space above the grill and there is sufficient ventilation around the grill.
