How does a chimney work?
a Chimney is essential to any heating system that burns solid fuel, designed to safely vent flue gases from the firebox of a fireplace or stove to the outside environment without filling the house with exhaust fumes.
Anatomy of a Chimney
The structure includes the chimney breast, which is part of the chimney extending into a room, and the chimney stack, the portion visible above the roof. Running through these, the flue serves as the main conduit for exhaust (AKA flue gases)—these are the byproducts of combustion, including steam, carbon monoxide, particulates and more.
A few inches above the top of the chimney stack, you’ll find the chimney cap, which protects the chimney from debris and elemental damage. Chimney caps also prevent animals like birds and squirrels from nesting inside the chimney (which, we can agree, is not ideal for you or the squirrel).
Taller Chimneys and the Stack Effect
Draft in a chimney is the driving force that moves flue gases from the firebox up through the chimney to the outside. This happens because of what we call the “stack effect”, which is the movement of hot combustion air from the fireplace or stove rising because it’s lighter than the cold outside air.
As this hot air goes up, it creates a lower pressure space at the base of the chimney. This low air pressure pulls fresh air into the furnace/ heating appliance to help the fire burn, and it also pushes the smoke and hot gases up and out of the top of the chimney. The strength of the draft depends on how much hotter the air inside the chimney is compared to the outside air, and how tall and well-built the chimney is.
Importance of Flue Insulation
The flue is usually lined with either clay tile liners or stainless steel liners, but some are even cast in place using a special polymer. These metal or tile liners, which provide a smooth, heat-resistant surface that minimizes buildup (soot, creosote, etc), keeps the chimney insulated and harmful chemicals contained until they can be vented away.
The insulation component is surprisingly important: maintaining a high temperature in the chimney is what creates the draft effect that pulls exhaust up and out of your home. Since the 1950s, building codes typically make this a requirement for new chimenys, but it’s just as important -if not more- to make sure an existing chimney has one when choosing a home.
Signs your Brick or Stone Chimney Needs Repair
Be vigilant for signs that your chimney may need attention. Backdraft occurs when smoke and gases are drawn back into the home instead of being vented out. Smoke in your living space, even when the fireplace is in use, should never happen and suggests a blockage or problem with the chimney’s draft. Additionally, if something is wrong with the flue (a crack in the clay liner, perhaps) this opens your home to a new realm of fire hazards.
Other signs that your chimney needs a check-up include
- Visible signs of damage to the chimney masonry, such as corrosion, cracks in the masonry, missing bricks, or deterioration of the mortar.
- A burnt wood smell when the fireplace isn’t burning,
- White stains on the outside of the chimney, which show moisture issues.
- Black, tar-like residue in your fireplace
Does your Chimney Work too Well?
That might sound tongue in cheek, but after 25 ft. or so in height, a chimney often works too well, especially in terms of draft creation. This strong draft can sometimes lead to issues like:
- Overfiring the Appliance: If the draft is too strong, it can pull more air through the fire than optimal, causing the fire to burn too hot. This can shorten the life of the wood stove or fireplace and can even be dangerous if it leads to overheating.
- Wasting Fuel: An excessively strong draft can cause the fuel to burn too quickly, reducing the efficiency of the heating system and leading to higher fuel consumption.
- Increased Wear on Chimeny Linings: The higher temperatures and faster moving flue gases can accelerate the deterioration of chimney linings and increase maintenance needs.
In these cases a stone or brick mason is often your best bet for shortening the stack.
Chimney Maintenance
Without chimneys, many homes would be filled with harmful-if not lethal- gases like carbon monoxide. Without ventilation, the heat in your home wouldn’t circulate, and you’d end up burning much more in order to maintain the same heat. Smoke and soot damage would accumulate, and you and your home’s health would dramatically suffer.
Risks of Creosote Buildup
The absence of a chimney would also raise the risk of creosote buildup. Creosote is a highly flammable byproduct of wood combustion that can accumulate in the heating system when gases are not properly vented. This buildup significantly increases the risk of chimney fires, which can be extremely dangerous and destructive.
Chimney Cap and Crown Maintenance
The chimney cap and crown protect your chimney from rain, animals, and debris. Fixing damaged caps and sealing any cracks in the crown can prevent bigger issues later. Check the cap regularly for any damage or rust, and make sure the crown doesn’t have cracks. Water entering through these cracks can damage your chimney from the inside.
Preventing Chimney Leaks
Chimney leaks often happen because of issues with the chimney cap, crown, or the flashing, which is the seal between the chimney and your roof. Keep these parts in good condition and waterproof to stop leaks. A waterproofing agent on your chimney’s exterior will be an extra layer of protection to help keep the water out of home and hearth.
Dealing with Chimney Blockages
Blockages in chimneys can be caused by bird nests, animals, leaves, or too much soot and creosote. A good chimney cap can keep most debris and animals out.
If you think your chimney might be blocked, stop using your fireplace right away and get a professional to check it. Using a blocked chimney can push smoke into your home and raise the risk of breathing in harmful gases like carbon monoxide.
Chimney Maintenance Tips
Keep your chimney in good shape by regularly cleaning out the ashes from your fireplace, looking for any damage, and making sure your fires burn efficiently. Burning only dry, seasoned wood helps reduce creosote buildup, which can cause chimney fires. Make sure there’s enough air flowing to the fire whenever you use your fireplace.
Importance of Annual Inspections
Chimneys should be inspected at least once a year by a qualified professional. These inspections help identify issues such as blockages, creosote build-up, structural damage, or wear that could lead to more severe problems if left unchecked. Regular inspections are crucial, especially before the heating season begins.
Scheduling Chimney Inspections
You should have a professional inspect your chimney once a year, preferably before you start using it regularly in colder months. If you use your fireplace a lot, consider more frequent inspections to keep everything running safely and smoothly.
Cleaning is Crucial
Along with annual inspections, chimneys often require cleaning with a damper to remove soot and creosote, substances that accumulate when wood is burned. Creosote is particularly dangerous as it is highly flammable and can ignite, causing a chimney fire. Professional chimney sweeps have the tools and knowledge to perform thorough cleanings, ensuring your chimney is safe.
Using the Right Fuel
Only burn appropriate materials in your fireplace or wood stove. Hardwoods, such as oak or maple, that are well-seasoned, burn more cleanly and efficiently than softwoods or freshly cut timber. Never burn treated wood, plastics, or other materials that can release toxic chemicals.
Installing Carbon Monoxide Detectors
Since chimneys vent combustion gases outside, any blockage or leak can lead to dangerous indoor accumulation of carbon monoxide (CO). It’s vital to have working carbon monoxide detectors in your home, ideally on each floor and near sleeping areas.
Find the Best Local Masonry Near Me at Ramos Masonry
Here at Ramos Masonry, we pride ourselves on being your local experts on masonry preservation and restoration, as well as providing brick and stone veneer installation, patio installation and repair, tuckpointing and more.
