I often get questions about the difference between a flue and damper. So, I put together this post
A flue is a metal channel that draws away gases and smoke from the fireplace. On the other hand, a damper is a metal plate at the bottom or top of a flue, which acts as a valve to regulate the passage of air. It also prevents precipitation or debris from falling onto the fire.
Let’s take a closer look at the differences (including a diagram) and if your fireplace needs one.
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What’s the Difference Between a Flue and a Damper?
The flue is also sometimes called the chimney lining when used with an open fireplace. You may think that it is your chimney that pulls the smoke up and out of your house when you’re burning fire, but this is incorrect.
Technically, the chimney is the cocoon of bricks and/or stone that surrounds the metal flue, insulating it from more flammable house materials like wood siding or roof tiles.
The flue itself is any metal tube through which ash, sparks, smoke, and gases are drawn up and away from the interior of your house.
If a flue is used with a fireplace, it releases these through a chimney opening. If used with a furnace or wood stove, it releases them through a vent on the roof or side of the building.
The flue is very important to the proper functioning of a fireplace, furnace, or stove. Fire needs oxygen to burn, and the flue creates negative pressure that pulls air up and through the combustion point. This updraft keeps the burn steady and hot, with more active flames and less smoke generated.
The damper, meanwhile, is an important element of a flue. It is a thick plate made of cast iron with a metal handle or chain to allow it to be opened when a fire is burning and closed when one is not.
On a furnace or wood stove, the damper will be at the base of the flue but not visible from the outside. In an open fireplace, it comes in two styles: throat damper and top-mount damper.
A throat damper is positioned at the bottom of the flue and about a foot above the firebox in an open fireplace, just out of sight from the outside of the fireplace. A top-mount damper will be at the top of the flue underneath the chimney cap.
Do You Need a Fireplace Damper?
You do! If you have any kind of combustion situation happening indoors—a fireplace, furnace, or wood stove—your damper becomes an important tool in containing and controlling that fire. It also seals the flue opening off from the outside when no fire is burning.
By opening the damper less or more, you control the amount of air moving past the fire and the cleanness of its burn. Think of it as a throttle for your flames.
Keeping it fully open when a fire is going in an open fireplace is preferred and recommended by the Chimney Safety Institute of America in order to keep the buildup of creosote in the home to a minimum.
For wood stoves, especially older models, the negative pressure (that is, the updraft of air pulled past the combustion point) created by the damper is an important element of temperature control.
These stoves are fully manual so setting the temperature of the flames is more hands-on than adjusting a dial. By opening the damper wider, you can make the fire in wood stoves burn faster. By keeping closing the damper partway to make the opening smaller, you’ll make it burn hotter and slower.
Because wood-burning stoves are often used to heat rooms or whole houses, keeping your fire burning slowly for a long time is ideal. This transfers more heat to the metal body of the stove, which means it releases more heat into the air around it.
Closing the damper when a fire is not burning seals off the fireplace from the outside. This keeps the conditioned (heated or cooled) air inside your home from escaping and also prevents precipitation, wind gusts, and intrepid animals from making their way down the flue tube into your home.
It’s worth mentioning here that you should check your damper and flue regularly for any kind of blockage or have a professional check it for you at the end of summer before fireplace season begins.
This is especially important if you have a throat damper instead of a top-mount damper. All kinds of flammable buildup or debris can make their way down a flue over time, even if you have a chimney cap, and this is the leading cause of chimney fires.
Do All Fireplaces Have a Damper?
Some older open fireplaces don’t have a damper, and they can function perfectly fine as fireplaces without one.
However, installing a damper (and possibly a new flue tube as well, if the chimney is old enough to be unlined fire brick) in these older fireplaces is a good idea too.
It helps to properly maintain the fireplace, to control the updraft, and to be able to seal it off when you aren’t using it.
You’ll be able to use your damper to keep the heated or cooled air of your home inside the walls of your house and keep the aforementioned critters, weather events, and debris (and sometimes very short-sighted children) outside of them.
Many newer wood stoves also lack a damper because their flues are engineered by the manufacturer of the stove to draw the perfect amount of air to make that stove function efficiently. It is still possible to install a damper in that situation but isn’t usually necessary.
Wood burning stoves already have a door on the front that can act as a seal against air movement, and their smaller flues are usually better and more easily defended from outside incursions but outside screens or caps.
How to Tell if Your Damper Is Open or Closed
A visual check is the easiest way to check if your damper is open or closed inside your fireplace.
You can visually check your fireplace damper by sticking your head into an (unlit!) firebox and looking upwards. If your fireplace has a throat damper, the metal plate of the damper will be just above your head.
If it has a top-mount damper instead, perform your check during the day—if the top of your chimney is dark, the damper is closed, and if you can see light coming in, it’s open.
Another basic but not foolproof method is to get close to your fireplace or wood stove and feel for a draft. You can even stick your hand into the (again, unlit) firebox to check for moving air.
Dampers are opened and closed by controls. This can take the form of a handle, chain, or rod. You should combine your visual check with moving the position of the control element to see what position moves the damper open or closed.
In general, though, a handle control will act like a drawer (pull to open, push to close), a chain control will need to be pulled all the way down and secured in that position to be closed, and a rod control will need to lift in order to push the damper open and pulled down to be closed.
Never, ever start a fire with the damper closed! This is dangerous both to the safety of your home and belongings and to your own health. Whenever you do build a fire, watch it for a while to make sure that the smoke is being drawn up through the damper and out of the flue.