While a fireplace can be a huge added bonus, it also requires a lot of work. But the key to becoming comfortable with your fireplace is understanding it. And one of the most important pieces is how your fireplace flue (or chimney flue) works. So, what is a chimney flue?
If you’re considering a rental unit with a fireplace, here’s what you need to know about operating and maintaining its flue so the fire stays warm and safe all winter long.
What is a chimney flue or a fireplace flue?
Your fireplace flue (or chimney flue) is a pipe or duct inside the fireplace that releases waste, much like a boiler vent or a breech for water heaters and furnaces do. Indoor fires, as you can imagine, produce a number of toxic and flammable gasses. The flue allows the dangerous gases — as well as the smoke and embers from your fire — to exit your home safely.
The goal of a flue is to let the gas and combustion by-products escape without exposing your indoors to the outdoors or losing the warm heat from your fireplace to the outside.
There was a time when the words fireplace flue and chimney were interchangeable. Today, it more commonly refers to either the vent pipe inside your chimney or a vent lining attached to the inside.
What does a flue do?
A chimney flue does a few different things. Its primary jobs are to keep you from getting sick and to keep your home safe. It moves those hazardous gasses, embers and smoke out of your home so you don’t breathe them in. They also keep them out of your living space so they don’t spark and create a house fire.
The flue also performs a couple of other important jobs when you’re not using your fireplace. When the fireplace is off, the fireplace flue’s damper (see below) seals off the chimney. When closed, the flue keeps air warmed by your heater or cooled by your air conditioning from getting out. This reduces stress on your HVAC system and saves you money on your electric or gas bill. As well, a sealed flue keeps wildlife from getting inside, which can ruin a perfectly good dinner party.
Another task of a fireplace flue helping makes the brick inside of your chimney more resistant to corrosion. Over time, corrosion can be caused by those same gas, heat and smoke by-products of burning wood. This corrosion, accelerated by soot and creosote, can destabilize the chimney and put your home at risk.
How does a flue work?
Heat rises. It’s a scientific principle we’ve been taught from the earliest age. And that’s basically how your chimney flue works. Your chimney is probably brick or masonry. These bricks retain the heat from your fire. The flue inside your chimney is most likely lined with tile or stainless steel. This protects your home and also helps replace the cold air inside your house with warm air from your fire.
Simply, the chimney, with the flue inside, runs from your fire to the outdoors. The flue uses what’s called the “stack effect” to direct gas, smoke and debris up and out of your home instead of into it. The stack effect occurs when the heat of your fire encounters the cold of the air outside. Under these conditions, the lighter gas travels up as the heavier cold air travels down.
Not only does the stack effect remove gas from your home, the cold air it’s forcing down feeds oxygen to your fire. This can obviously bring cold air into your home, defeating the entire purpose of your fire. Enter the damper.
What about a flue damper?
Basically, your flue damper is just a small metal or ceramic flap above your fire or at the top of your fireplace flue. This flap controls the size of the chimney flue’s opening. This regulates the amount of heat you’re getting from your fireplace and allows smoke to escape up the flue. The damper aperture is controlled by a lever, handle or pull chain.
The adjustment of the flue as you use your fireplace is critical. If your flue damper is manual, there are a few things you need to know. When starting your fire, your flue should open all the way, for optimal heat, safety and keeping smoke at bay. As your fire burns, it should open just enough to pull the smoke from the fire slowly up through the chimney and outside. The damper is basically a thermostat controlling the intensity of your fire by controlling the oxygen flow.
A damper closed at the wrong time will fill your house with smoke. A damper open at the wrong time will cause all your heat to escape. But beware. The flue lever or handle gets very hot — make sure to wear hand protection. Luckily, many modern fireplaces have automatic “barometric” dampers that make the entire process hands-off.
And as stated above, to keep cold, rain and nature from getting inside your house when you don’t have a roaring fire going, the damper must stay closed.
How do you keep your flue safe?
Cleaning, cleaning, cleaning. Regularly running fireplaces cause soot and a substance called creosote to build up along the chimney flue. These substances are flammable and too much of it is at risk to catch on fire and spread.
Creosote can be reduced in a wood-burning fireplace with a commercially-available creosote log. A creosote log is a log-shaped cylinder of pressed wood treated with chemicals that help remove creosote from your fireplace flue. While they are easy to use and inexpensive, they cannot remove bigger non-creosote debris and are filled with said chemicals. That’s why it is recommended to have your chimney and your flue professionally cleaned (and inspected) by a chimney sweep yearly. (Chim chiminey, chim chim cher-ee.)
Additionally, over time — particularly with tile chimney flues — damage and wear are inevitable. If you notice excess smoke, more difficulty keeping your fire going or bits of tile having broken off and fallen into your firebox, consider having your flue repaired or relined. A damaged flue can allow the corrosion from your fire to seep into the brick or masonry.
As well, you should keep and maintain carbon monoxide monitors within your house near your fireplace. Your chimney flue is designed to keep these gasses outside your house, so a detector can warn you when you have an issue. And store a fire extinguisher nearby your fireplace as well.
Enjoying your cozy fireplace
For safety as well as efficiency, it is important to understand your chimney flue. Now you’ll feel more confident as you preview apartments or rental homes with fireplaces.
And if you choose a rental with a fireplace, we know you’ll enjoy the cozy factor. Plus, your apartment pets will love laying down in front of it all winter.
