Gas Logs vs. Gas Inserts

Three options, three different appliances

Vented gas logs

Vented gas log sets are tested and labeled as vented decorative appliances. They go into a real, working wood-burning fireplace. One manufacturer's manual we reviewed requires installation only in a solid fuel fireplace with a working flue, requires the damper to be fully open while burning, includes a damper clamp so the damper cannot close fully, and requires glass doors to be open while the logs burn.

Because the flame burns in an open fireplace with the chimney open, most of the heat goes up the flue, much as it does with wood. Vented logs are chosen for convenience and appearance, not heat.

Vent-free gas logs

Vent-free logs are designed to burn without a chimney, releasing combustion products, including water vapor, into the room. They rely on safety features and room-size limits. One vent-free log manual we reviewed describes an oxygen depletion sensor that shuts the burner off before room oxygen drops below 18 percent, gives a formula for the maximum input allowed for a room's volume, prohibits units over 10,000 BTU per hour in bedrooms and bathrooms, and warns that tight homes may see excess heat or moisture.

The same manual notes that state and local codes may allow only vented operation. Before considering vent-free logs, check with your local construction office. Some homeowners also find the moisture and odor objectionable. The US Consumer Product Safety Commission warns that fuel-burning appliances can cause carbon monoxide problems when improperly installed, poorly maintained, vented poorly, or misused.

Direct-vent gas inserts

A gas insert is a sealed firebox that slides into the fireplace opening. Most are direct-vent: one pipe brings outside air in for combustion and another carries exhaust out, both running up the chimney to a termination cap. Because the fire is sealed off from the room and the insert has a heat exchanger, much more of the heat stays in the house than with logs.

Insert manuals set conditions for the chimney. One we reviewed requires the existing chimney to be clean and in good working order, lists minimum flue sizes for masonry and factory-built chimneys and a height range, and allows the damper to be blocked open or removed. Another manufacturer prohibits connecting the insert to a flue that serves a separate solid fuel appliance.

What to expect for heat

An open fireplace sends most of its heat up the chimney. EPA notes that traditional open fireplaces lose over 90 percent of the fire's heat that way. Vented gas logs burn in that same open setting, so they add little warmth to the room. An insert closes the opening and transfers heat to the room through its glass and heat exchanger, often with a blower. If your goal is to heat a room on winter evenings, that difference should drive the decision more than the look of the flame.

Service and upkeep

All gas appliances in a fireplace need periodic service. Log sets can shift, burner ports can clog, and pilot assemblies collect dust. Inserts have glass gaskets, vent connections and termination caps that should be checked. Manuals call for periodic examination and cleaning of the venting system by a qualified agency. Annual inspection of the chimney and appliance is a reasonable routine.

Choosing between them

• You want occasional ambience and keep the option of a wood fire: vented logs fit, provided the fireplace and chimney are in working order.
• You want real heat from the fireplace: a direct-vent insert is designed for that.
• You are considering vent-free: confirm local code first and read the room-size limits in the manual.
• Your fireplace is factory-built: check its manual. Some prohibit inserts without the manufacturer's approval. See factory-built fireplaces.

What the chimney needs either way

Gas burns cleaner than wood, but a gas appliance still depends on its chimney. CSIA notes that chimneys serving gas appliances can be blocked by nests and debris and should be inspected annually. Before a gas log set or insert is installed in a fireplace that has burned wood, the flue should be swept so creosote odors do not come into the room, and the chimney should be inspected. CSIA lists the addition of an appliance as a reason for a Level 2 inspection.

Permits

In New Jersey, some towns list installing a gas insert into a fireplace as permit work. Gas piping work is also regulated. Check with your local construction office before work begins.

Both logs and inserts need a gas line at the fireplace. Chimney 911 connects gas logs, gas fireplaces and inserts to an existing line. We do not run or install new gas lines, so if your fireplace has no line yet, a plumber or your gas utility handles that part first.

Next step

If you are weighing logs against an insert, request an assessment of your fireplace and chimney. See our gas log and gas fireplace installation and gas fireplace service pages. Converting from wood? Read converting a wood fireplace to gas.

Questions homeowners ask

Sources

1. Masonry Fireplace Industries Virginiana vented gas log manual
2. Grand Canyon Gas Logs vent-free log set manual
3. Kozy Heat Nordik 34i gas insert installation manual
4. Valor LX1 co-linear venting specification
5. CSIA: Homeowner Resources and FAQ
6. Borough of Allendale, NJ: Do I Need a Permit?

This guide is general information. It can't diagnose a specific chimney; an inspection can.