Before shopping, use a tape measure to record these four dimensions in your firebox:

Your log set size is limited by the space required for the burner and its control system. Use these general "subtraction" rules for the front opening width:

Measure from the fireplace floor to the top of the front opening. 2. Sizing Guidelines by Valve Type

Subtract 4 inches from your front width.

Measure from the front opening (behind any lip or ledge) to the back wall.

How To Measure for and Choose a Gas Log Set - Fireplace Doors Online