For open-air areas, having a lot of heat coming out of your device is important. Especially if you live in a part of the country with very cold winters. For indoor areas or enclosed spaces, you actually don't need nearly as high of a heat output. This is because enclosed spaces retain the heat much better. Having a device that puts out an incredibly high amount of BTUs can actually make it much less efficient when used in enclosed spaces. It also has the tendency of drying out the air, or overheating the area. A good amount of BTUs for an enclosed area is around the 5,000-5,200 BTU amount.