Outdoor gas fireplaces can give off a significant amount of heat, depending on their size and design. Some outdoor gas fireplaces are designed to provide a more contained, focused heat source, while others may produce more radiant heat that spreads outwards from the fireplace. In general, larger outdoor gas fireplaces will produce more heat than smaller models. Additionally, outdoor gas fireplaces with open designs will typically give off more heat than those with closed or semi-enclosed designs.