What is the horizontal clearance between a gas fireplace exhaust and a window?
The clearance for a direct vent gas fireplace horizontal exhaust is typically 12 inches from side of operable window.
Or what the manufacturers instructions state.
Make a habit of locating the manufacturer information under the fireplace so you can download the manufacturer installation instructions. Usually you’ll find a data plate similar to what you’d find on a furnace.
Then, one can look up the specific unit and KNOW what the specs are…