The answer depends on the glass used in the sunroom. There are a variety of different glazing options used by each sunroom manufacturer, such as single or dual pane glass. Each option allows more or less heat into the room, measured as Relative Heat Gain.
The glass with the lowest Relative Heat Gain (39) is called CONSERVAGLASS PLUS™. It’s only available on sunrooms manufactured by Four Seasons Sunrooms. CONSERVAGLASS PLUS™ blocks 85% of the sun's heat, helping you significantly reduce cooling costs.
For more information, go to: http://www.ambianceadditions.com/sunrooms/sunroom-windows.html