All of our wood stoves and fireplaces require a chimney, either a masonry or A vent stainless steel chimney. The diameter of the chimney must match the size of the fireplace flue collar to effectively vent the products of combustion. Consequently, an existing chimney may need to be lined with a stainless steel liner to meet venting requirements of a specific fireplace. Gas fireplaces that fall under the category of B vent or natural draft fireplaces, also require either a chimney that is lined with a flexible aluminum or stainless steel liner, or they can be vented using B vent if no chimney exists. Direct vented or vent free fireplaces do not require a traditional chimney.