B-Vent gas fireplaces utilize the same passive draw methodology as wood burning products - drawing in room air to aid in combustion. Though the fireplace pulls room air, it is a minimal amount compared to the amount of air a traditional wood burning fireplace uses. This is a gas-only technology and cannot burn any other fuel source other than natural gas and liquid propane. B-Vent products use smaller "Class B" furnace flue systems which range from 5" to 8" in diameter, depending on the BTU output. B-Vent fireplaces or stoves can only exhaust vertically, making the install of a B-Vent unit only suitable in certain applications.