Vented vs Vent-Free Gas Logs: Which Suits Your Fireplace?

Short answer

Pick vented logs for the look of a wood fire in a working masonry fireplace, with the damper open while they burn. Pick vent-free logs for heat, only where code allows them, in a room that meets the size in the manual, with the damper closed as the manual directs.

Two ways to burn in a fireplace

A vented log set sits in a wood-burning fireplace with its chimney damper open, sometimes clamped open permanently. The burner produces a large, lazy yellow flame that licks the logs, and its exhaust goes up the chimney with most of the heat. A vent-free set burns hotter and cleaner with a smaller, bluer flame so it can run with the damper closed; its heat and combustion products stay in the room, and it carries an oxygen-depletion sensor.

Both kinds sell on their BTU input. A vented set's BTU figure tells you how much gas it burns, not how much heat reaches the room; a vent-free set's BTU input is much closer to the heat you feel.

Compared

Vented and vent-free gas logs
	Vented logs	Vent-free logs
Damper	Open while burning	Closed (per manual)
Flame	Tall, yellow, wood-like	Smaller, bluer
Heat to the room	Little; most goes up the chimney	Most of it
Indoor air	Exhaust leaves through the chimney	Combustion products and moisture stay in the room
Where allowed	Working wood-burning fireplaces	Where local code permits, in rooms sized to the manual

Log sets in our catalog: vented RealFyre SDP-24 Vented Gas Log Set and Duluth Forge FNVL24-1 Natural Gas Vented Gas Log Set; vent-free Real Fyre G18 30-Inch Natural Gas Vent-Free Gas Log Set, Real Fyre G10 24-Inch Natural Gas Vent-Free Gas Log Set and Real Fyre S9-24 + G9-24P Propane Vent-Free Gas Log Set.

Matching a set to your fireplace

Measure the firebox: front width, rear width, depth and height. Log sets are sold by nominal width (18, 24, 30 inches and so on), and the manual lists the minimum firebox dimensions for each. A set that is too big for the box can overheat the surround or roll flame out of the opening; too small looks lost. Our product pages show the width each listing states.

Then check the fuel (natural gas or propane), the ignition (match-light, manual safety pilot, or remote-ready millivolt valve) and any remote or thermostat the set supports. A remote-ready valve can be paired with the kind of fireplace remote we list in the hearth gear hub.

Codes, rooms and safety

Vent-free sets carry the same limits as other vent-free appliances: a minimum room size for their BTU input, often an altitude limit, and restrictions or bans in some jurisdictions and in bedrooms. Vented sets need a sound, open chimney; NFPA advises chimney and heating system inspection and cleaning each year before the season.

SafetyKeep the chimney damper open whenever vented logs burn, follow the manual for vent-free sets, and keep CO alarms on every level of the home (CPSC).

Which to choose

You want the look of a wood fire and have a working chimney: vented logs.
You want heat from the fireplace and local code allows it: vent-free logs sized to the room.
You want heat and the room is small or a bedroom: a direct-vent insert, not a log set.