Should You Open the Flue on a Gas Fireplace?

There is nothing like the feeling of the warm glow of a fire on a chilly night.  However, when you are using a gas fireplace, there are some notable differences from your standard wood fireplaces or wood stoves.  It would be best if you had a clear understanding of safety procedures.  One of the most critical components of a gas fireplace is the proper use of the fireplace flue. We've researched how the flue works and when to use it, so you will be prepared to light that gas fireplace.

Our research shows that the flue on a gas fireplace should remain open during use or when the pilot light is lit.  If the flue is closed in either instance, you risk a greater chance of carbon monoxide poisoning or a spark-induced structure fire due to a buildup of toxins emitted by propane or natural gas burners.

Now you know they leave the flue open, but where is the flue located and how do you operate it? Please keep reading, as we describe the function of the flue and damper for gas fireplaces. We'll also delve into the differences between vented and ventless gas fireplaces, so you'll know exactly what you need to install a safe unit in your home.

A gas fireplace with a white colored mantel, Should You Open the Flue on a Gas Fireplace?

The Gas Fireplace Flue

Among the other components of a gas fireplace (or gas logs), the flue is a chimney, pipe, or ductwork that allows gasses such as carbon monoxide to escape without losing fireplace heat. A flue damper is located inside the flue.  The damper is typically in the shape of your internal chimney pipe and resembles a metal flap.  It has a long thin piece of metal attached to it, which is called a lever.  On the other end of the lever is a handle that allows you to open or close the flue damper.

The damper's handle is metal with no protective coating.  It looks like a long thin bar with a hole drilled in the end.  Along the top of the lever, there are notches cut out that are zigzag-shaped (resembling sharp teeth) and designed to catch on the edge of the flue to lock the damper in place.  It is interesting to note that flue designs have changed over the years.

At one time, a popular design resembled a chimney cap, which was operated by a small chain that ran down the full length of the chimney to the fireplace hearth inside of the home.  Ultimately, the purpose of the damper is to control how much smoke (or carbons) escape up the chimney and how much heat stays in the room.

How do you open a fireplace flue?

The process of opening a fireplace flue is relatively simple.  Before you fire up your gas logs, though, you need to make sure that the flue is open.  Opening before lighting a fire is strictly for safety, being that this entire design is metal, and you risk severe burns if you attempt to adjust the damper after the gas logs ignite.  The flue damper handle (or lever, depending on the style of gas logs you have) should be marked to indicate "open" or "closed." If it is not marked, the typical style of the lever requires pushing it to open the flue or pulling it towards you to close it.  Newer electric flue damper model designs allow you to open or close the flue with a simple push of a button.

Do all gas fireplaces have a flue?

Not all gas fireplace designs are the same.  There are two significant types of gas fireplaces:  vented and ventless (or vent-free).  Yellow flame gas logs are primarily classified as vented. They behave much like a standard wood-burning type fireplace in that the level of heat, chimney soot, and carbon are comparable to each other.  New models usually have a built-in safety feature of an open flue during use.  Flue and chimney use is mandatory with vented gas logs.

The second type of gas fireplace, classified as ventless, utilizes blue flame logs.  They tend to burn hotter and cleaner than their yellow log counterpart.  They can be installed in an existing wood fireplace box (with the chimney flue closed) or in a freestanding cabinet with the need for a flue or chimney.

What kind of chimney does a gas fireplace need?

A vented type of gas fireplace does not necessarily need a chimney.  It does, however, need some kind of venting system installed, whether it be a horizontal side vent through an exterior wall or a vertical vent extension through the roof of the structure.  You can retrofit a wood fireplace to accommodate a gas log insert and use the pre-existing chimney.  The Chimney Safety Institute of America does recommend having your chimney venting system evaluated by a Certified Chimney Sweep ™  to ensure that your entire system is operating most safely and efficiently.

Ventless gas fireplaces, such as the freestanding cabinet style, are manufactured to be operated without a chimney or venting system, though proper air movement within your home is encouraged.

When should I close my fireplace flue?

As a general rule, if you have a gas log fireplace, you should never close your flue when in operation.  If the fireplace is not operating, but the pilot light is lit, you should not close your flue. The reasoning is that when gas fireplaces have access to fuel, they can emit dangerous levels of carbon monoxide that may prove fatal to their users if not properly vented.

Discover additional information through The International Association of Certified Home Inspectors.  If you are certain that you will not be using your gas fireplace for an extended period, such as warmer summertime months, it is safe to close your fireplace flue.

In Closing

A gas fireplace is a terrific addition to any home.  It certainly burns cleaner than your standard wood fireplace.  Before the cold season starts, it is important to remember that you should always schedule a maintenance appointment for your gas fireplace and flue with a Certified Gas Technician.  Maintenance should take place at least once per year.  You should also ensure to install carbon monoxide correctly and insert fresh batteries.  By understanding how to safely operate your gas fireplace and taking the proper steps for maintenance, you are sure to enjoy your gas log fire for years to come.

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