Fireplace Flue vs. Fireplace Damper: What Homeowners need to know

Fireplace flue, fireplace damper. If you are confused about the difference, you aren't alone. The words are used incorrectly (and interchangeably) so often that the meaning of each has become muddled. But if you ask any fireplace specialist, the difference between the two couldn't be clearer.

A fireplace flue and a fireplace damper are not the same thing. The flue is the opening or passageway that the smoke or other combustible gas from the fire exits the house. The damper is a mechanism that opens or closes access to the flue.

Now that we've cleared up the difference between the two terms, there's a lot left to learn in order to safely enjoy your fireplace. Keep reading to learn how your damper and flue work, how to keep them clean,  and how and when to use them (and when not to)!

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Fireplace Flues And Dampers

Let's discuss what each of these is in more detail!

Fireplace Flue

A flue, again, is the opening that allows combustible gas to exit the house from the fireplace. A fireplace without a flue would quickly fill with smoke, carbon monoxide, and other toxins. The flue on a fireplace is always open - it's whether or not the damper is open or closed, and the resulting access to the flue, that changes.

Almost every kind of fireplace has some sort of vent for this purpose, even if they do not have a noticeable chimney built into the house. Many gas stoves or pellet stoves use a stainless steel chimney pipe that vents outside through a hole in the wall, and then up toward the roof.

The only fireplace without a flue is the aptly named ventless fireplace. These are commonly electric, though they can also be gas.

It's important to note that gas or pellet stoves still require a combustible fuel to burn. Ventless gas fireplaces are specially designed to require a very small amount of fuel, which means very little is exhausted back into the air. This small amount can still be a source of toxins such as carbon monoxide, and there's a lot of debate on safety.

Ventless gas fireplaces are illegal in California and many individual municipalities, though ventless gas manufacturers have stated they are safe to use.

Should The Flue Be Open On A Wood Fireplace?

Just before starting a fire in a wood fireplace, you should open your damper and leave it open the entire time that the fire is burning. It's necessary to leave the flue open so that the smoke and gases created by the fire can safely be drawn up the flue and outside.

Except for gas fireplaces, the damper should be closed the rest of the time. The pilot light on a gas fireplace remains on all the time, even when the fire is not burning. This expels small amounts of gas into the air, which need to continually vent outside through the open flue. For this reason, the damper on a gas fireplace is left open at all times.

Fireplace Damper

You may not need a damper for your fireplace. It really depends on what kind of fireplace you have.  Ventless fireplaces do not have a flue, so they do not need a damper. Vented fireplaces should always have a damper. Occasionally, an old wood-burning fireplace built before damper installation was standard may not have one, though one can be added easily by a fireplace professional.

In pellet or wood stoves (not fireplaces), the damper is used to adjust the airflow to the fire, controlling the burn. In a wood fireplace, the damper has no real effect on the air intake. However, it's still important to be able to close the flue when you want to retain heat and open the flue when you need to expel smoke.

Should A Fireplace Damper Be Open During The Summer?

In a wood stove, an open damper allows air from inside the house to escape outside. This raises heating bills in the winter and air-conditioning costs in the summer. Some people, without air conditioning, think that leaving the damper open will cool down the house. But an open damper is a lot like leaving a door open in order to cool off - probably not worth the minimal effect.

This has nearly no effect on the temperature of the room and allows animals such as birds an opportunity to get in the house. It can also bring unpleasant smells from the creosote in the chimney, which is affected by humidity. Shut the damper, shut the door, and turn on a fan.

How Do I Know If The Damper Is Open Or Closed?

If you're about to start a fire and are unsure if the damper is open (as it should be), it's easy to tell the difference. Simply lean into the fireplace with a flashlight and look up the flue. Often, the damper is toward the bottom of the flue, and you can tell immediately if the damper is open or closed. If your view is obstructed by something blocking the flue, the damper is closed. If you can see clear up the flue to the sky, the damper is open.

How Do You Know If Your Chimney Flue Needs To Be Cleaned?

Sometimes a chimney problem is obvious. Maybe every time you start a fire, the room fills with smoke even though the damper is open. Maybe there's a constant backdraft from the chimney. These can be signs that a chimney is partially obstructed by creosote and needs to be cleaned.

Other signs that your wood-burning chimney needs cleaning include:

  • Soot or creosote dropping from the flue into the firebox (where the logs and fire are)
  • Visible, large, puffy creosote formations
  • A thick, dark, shiny coating on the flue (this is creosote build-up)

Other times, the flue needs cleaned but so far is still functioning as expected with no obvious signs. The only way to tell if a properly working flue is ready for cleaning is to either schedule a professional inspection or inspect it yourself. In either case, the flue should be checked at least once a year.

How To Inspect The Flue Yourself

To inspect a wood-burning chimney yourself, you will need a dust mask, safety goggles, flashlight, and fireplace poker. Note that the inspection of a gas fireplace is different and the instructions are below.

You will first want to check for a downdraft from the chimney. You can tell this by feeling for air movement from the chimney. You can also tape a napkin to the fireplace and see which way it seems to blow. If a downdraft is present, open the windows as needed until the airflow changes.

Then, reach above the open damper with the poker. Scratch the black surface on the walls of the flue. If the scratch you make through the black creosote is 1/8th inch deep, your fireplace needs to be cleaned. If it's more than 1/4th inch deep, you should stop using the fireplace altogether until it is cleaned.

You'll also want to visually inspect for cracked or loose tiles. Or in the case of a metal flue liner, uneven joints. Check for obstructions and debris also.

What About Gas Fireplaces?

Creosote build-up is a concern in wood-burning fireplaces only (this includes pellet stoves). You will still need to inspect your gas fireplace once a year for obstructions or other safety issues. It's recommended that you use a professional, and have your entire HVAC system inspected.

To check the fireplace yourself, you'll want to follow these steps:

  • Clean the inside (logs, etc.) from dust.
  • Clean the blower from dust.
  • Examine the glass doors to ensure there are no cracks and they seal completely.
  • Check the pilot light. If you see an immediate concern such as loose wires, call a professional. If everything seems to be in order, test the pilot.
  • Check the vent. Make sure there are no obstructions such as animals, leaves, or other debris.

How Do You Clean The Fireplace Flue?

If you hire a chimney sweep to clean your chimney (which costs anywhere from $100-$300, according to Homeadvisor), make sure to hire one who is certified. In America, the certification board is the Chimney Safety Institute of America.

You can also try a creosote sweeping log, which is accepted by the Chimney Safety Institute of America. This product works by starting a normal fire in your fireplace, then adding the log. The log burns for about 90 minutes. This product can stretch the time between cleanings but does not replace yearly inspections or cleaning altogether.

The log has special minerals that will stick to and break down creosote deposits in the chimney. It does not burn off the creosote, but it loosens the sticky tar-like substance that adheres creosote to the chimney walls. The manufacturer claims that tests have shown one log can reduce creosote deposits by as much as 60%.

Click here to see the creosote sweeping log on Amazon.

Cleaning The Flue Yourself

If you want to clean it yourself, you'll need a few things.

  • A stiff wire chimney brush. Look for the following things:
    • Select a brush that matches the flue shape (round, square, or rectangle).
    • It will also need to have the correct diameter. Measure your chimney.
  • You'll also need a rod, which comes in sections that link together. You will use as many sections as needed to extend the brush high enough to reach the whole way through the chimney. This means that you need to measure or know the length of the flue to determine how long of a rod you will need. The rod is typically one of two materials, though you can use sections of either material interchangeably.
    • Fiberglass, which is for flues that are straight up.
    • Nylon, which is flexible for flues with bends.
  • A noodle brush to clean the smoke shelf.

Click here to see this Schaefer noodle brush on Amazon.

  • You will also need a drop cloth, a shovel, and a bucket. If you don't have a fireplace shovel already, you can select one like this version by Rocky Mountain.

Click here to see this fireplace shovel on Amazon.

For more instructions on how to perform the cleaning, you can watch this YouTube tutorial:

In Closing

A fireplace damper and a fireplace flue are not the same. Remember that the flue is the path that smoke and other toxins can escape the home; the damper is the mechanism that opens or closes the flue.

It's important to keep the damper open while the fireplace is in use to keep smoke from entering the home. The flue should also be checked at least once a year to make sure that it is safe for continued use.

And as always, enjoy your fireplace!

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