If your gas fireplace has a chimney, you must also open the flue to allow carbon monoxide and other dangerous gases to escape. (If you have a ventless gas fireplace, you can skip this safety step.) ...

the ventless fireplace. Ventless fireplaces are designed to burn gas more efficiently than vented versions, resulting in far ...

Without a liner, the chimney is often too wide, uneven, or damaged to work properly — especially with today’s efficient wood stoves, which produce lower flue gas temperatures than open fires.