In almost every situation, it’s a better idea to keep your fireplace doors open while the fire is going. Not only does it prevent the fireplace doors from getting too hot, it also allows the heat of the fire in the room to warm it. But, as long as you have a masonry fireplace that has ceramic glass, you can close your doors!
Ceramic glass can withstand temperatures up to 1400F. The typical masonry fireplace fire only gets up to about 1200F, so this type of glass can handle the heat. Because of the construction of manufactured fireplaces though, this only works on masonry fireplaces. And, even on your masonry fireplace, it’s a good idea to make sure that the grate and logs be at least 4-6” from the glass. It’s also really important not to burn anything in the fireplace that shouldn’t be there—stick to logs, don’t burn cardboard!
Not sure how to tell the difference between ceramic glass and tempered? The easiest way to tell the difference between these two glass types is in how it breaks. Tempered glass will shatter where as ceramic glass will crack and break in big pieces.