Rumford Fireplaces have a different configuration than a conventional fireplace, the sizing methodology is also different. With conventional gas log sets, the set size is based on the largest log in the set (the set's nominal width). However, with Rumford Gas Logs, the sizing is based on the width of the fireplace (see size chart link).
Traditional Rumford Fireplaces have a wide front, narrow back, shallow depth and a height nearly as tall or taller than its width. They have a unique aerodynamic throat and smoke chamber that create greater efficiency than traditional fireplace designs. The shallow back and steeply angled sides effectively radiate more heat into the room than a conventional fireplace. Traditional gas log sets will not fit properly due to this steep taper. Also, most Rumford Fireplaces are vertically oriented (taller than their width), so a vertically oriented log stack is a better design fit for the opening.