Tag Archives: firebox

What is a Masonry Chimney?

A masonry chimney on the exterior wall of a home

Just like automobiles that have different manufacturers and models, the same goes for fireplaces and chimneys.

Here in Southern California, there are primarily three different types of open fireplace systems–1) masonry chimneys; 2) prefabricated, factory-built systems; and 3) Rampart General Pre-Cast systems. Since I’ve already addressed Rampart General Pre-Cast systems in the past, this post will be about the masonry chimney.

The History of the Masonry Chimney

These masonry systems have been around for many centuries and are tried and true. They are constructed on-site with bricks, stone, concrete blocks and mortar. Masonry systems are built by hand, brick by brick. If the system is built properly and maintained regularly and there are no extenuating events (such as earthquakes and wildfires), they will last a century or more. In fact, it’s not uncommon to see masonry chimneys still in use in houses built in the 18th and 19th centuries.

Unfortunately, due to the high cost of labor, these systems haven’t been constructed since the mid-1980s here in Southern California except for in high-end, custom-built homes.

For a fireplace to work properly, there is a formula involved in building a masonry chimney system. Some of the factors in this formula have to do with the height of the chimney, the diameter of the flue pipe, and the height/width of the firebox opening. If a system isn’t built properly, the chimney will never draw properly and will have ongoing smoking problems.

Components of a Masonry Chimney and Fireplace

It’s important to know the various components of a masonry chimney:

Flue cap – The chimney cap consists of spark arrestor material with a solid lid. It provides three primary benefits: 1) It prevents embers from getting on the roof; 2) It prevents birds, rodents and other critters from entering the home through the chimney; and 3) Flue caps with solid lids will also prevent most of the rain from coming down the flue lining. Without the solid flat lid of the cap, rain would land in the smoke shelf which may cause damage to the damper and may deteriorate the firebox.

Crown – The crown is a concrete or mortar surface at the very top of the chimney structure. Its purpose is to direct water Masonry chimney componentsaway from the structure. A crown can also be referred to as a “wash” or a “splay.” A cracked crown will allow moisture to get into the chimney structure, eventually creating cracks in the chimney structure.

Flue – The flue is the passageway from the firebox to the top of the chimney structure. In a masonry chimney, the flue is lined with a flue lining typically made from terra cotta, pumice or metal.

If the flue lining is cracked, broken or if the mortar joints are missing between the flue tiles, the system cannot be used because of heat transference or deadly carbon monoxide leaking into the house. There are three primary methods for repairing cracked flue linings–1) relining the system with a stainless steel pipe; 2) installing a stove insert with a metal pipe to the top of the chimney structure; or 3) a poured cement, cast-in-place system.

In addition, older systems may not have a flue lining at all (which is referred to as an “Unlined Chimney”). In this case, the system cannot be used until it has been repaired.

Flue tiles – A flue lining inside a flue is basically a vent pipe. This pipe is not one solid pipe. In most cases, the pipe (typically terra cotta or pumice) is made up of pipe sections called flue tiles. Each flue tile (pipe section) is anywhere from 12″ to 24″ tall. In between each flue tile is the mortar. There should not be any gaps or voids in the mortar joints.

Smoke Shelf – A horizontal shelf located behind the damper to prevent down drafts and to collect debris that has fallen down the chimney.

Damper – The device that opens and closes so that heat is not lost from the home when the fireplace is not in use. Some dampers can be installed at the top of the chimney flue.

Lintel – A horizontal metal piece that extends over the entire width of the firebox opening at the top of the firebox opening. It is a structural part of the firebox. Here’s important information on why you never want to remove a lintel.

Firebox – The area of the fireplace where the fire is burned.

Exterior Hearth Extension – The area that extends in front of and to the sides of the firebox opening. The exterior hearth extension should be made from non-combustible materials and should be differentiated from the rest of the room’s flooring.

Ash Dump – Not all masonry systems have an ash dump. This is the area below the firebox where the ashes can be swept down into. A firebox with an ash dump will typically have a metal plate in the firebox’s floor. This metal plate can be opened to brush the ashes below.

Clean-out Door: The clean-out door is located on the outside of the chimney structure near ground level to clean out the ashes from the ash dump.

Unlined Masonry Chimney

Before the early 1900s, masonry systems were not constructed with a flue lining. We refer to those systems as “Unlined Chimneys.” According to the Chimney Safety Institute of America, “Never use a chimney that does not have a liner or has a damaged or improper lining.” [Public Safety Bulletin issued by the Chimney Institute of America: The Importance of Flue Lining in Your Masonry Chimney.] Here in San Diego, however, we have seen unlined chimneys as late as the early 1960s.

When these unlined systems were originally built, the masons used a material called parging (like stucco). They hand-coated over the bricks and mortar joints inside the chimney flue. With time, age and usage, this parging material has worn away, leaving the bricks and mortar joints exposed. In addition, back then the masons used a lot of sand in their mortar. Eventually, these mortar joints disintegrate, leaving gaps and voids. This creates a potentially dangerous situation.

If the unlined chimney is structurally sound and there are no other issues with the system, the system can be “relined.” This is a method where a stainless steel pipe is installed inside the chimney structure. However, if the metal lining is not installed properly or is undersized, the fireplace can be dangerous and/or will not ever draw properly.  Relining a chimney should only be done by a licensed and qualified chimney professional.

Make sure to use a CSIA Certified Chimney Sweep to inspect your system and sweep it if needed. If your masonry chimney is maintained, it will give you warmth and comfort for many years, decades and maybe even centuries to come.


Caveat: Chimneys are built differently in various regions throughout the country. What is common in one region may not be common in another. This information provided here is based on what we see in Southern California.

Spring flowers with the words "Time for a Spring Cleaning"

10 Easy Steps to Spring Cleaning Your Fireplace

Spring flowers with the words "Time for a Spring Cleaning"Spring has sprung and it’s time for some spring cleaning, and that includes your fireplace! Many people would agree that one of the least favorite household chores is cleaning out the fireplace after the last fire of the season but it doesn’t have to be difficult with some easy tips. Ashes should be removed from the fireplace during the spring to avoid what we refer to as “Stinky Chimney Syndrome.”

10 Easy Steps to Cleaning Out the Fireplace

1. Make sure the ashes are completely cool before starting. It’s best to wait at least 48 hours after a fire in order to allow the ashes to completely cool.

2. If you have respiratory problems, asthma or allergies, use a mask. Breathing in the fine particulates can irritate the lungs of people who have respiratory problems. Better yet, if you have any kind of lung problems, let someone else in your family do this chore!!

3. Place plastic sheeting around the fireplace to ensure ashes don’t get on your carpeting. Wipe down the grate and place it to the side on the plastic sheeting.

4. Remove about a cup of ashes from the firebox and set aside. This will be used later to clean the glass in the glass doors.

5. Sprinkle some slightly damp, used coffee grounds on top of the ashes inside the firebox. This will settle down any dust and cut down on the fly-away ash, making it easier (and healthier) to sweep up.

6. Using a whisk broom and a dust pan, place the chunks of wood and ashes in a metal container with a lid. Sweep each interior wall of the firebox from top to bottom.

7. Brush each firescreen mesh from top to bottom. We find, for whatever reason, that firescreens tend to collect “dust bunnies.”

8. Place the metal container of ashes outside but never place the metal container on a wooden deck or patio if the ashes are warm. We’ve heard too many stories of houses burning down from this simple mistake.

9. Avoid harsh chemicals to clean the glass doors. Simply dip some damp newspapers in the ashes that you set aside and rub the glass to remove the soot and build-up. Because the ash is somewhat gritty, it’s much better at removing the residue off the glass than normal glass cleaners. Afterwards, spray white vinegar on the glass and wipe down with a soft rag to get the glass sparkling clean.

10. The last step is to close the damper. An open damper is the same as an open window. During the summer when you’re running your air conditioning with the damper open, all you’re doing is sucking the heat down the chimney and into the house, totally defeating the whole purpose of having your air conditioning on. Close the damper and you will save money on your electric bills. Just don’t forget to open your damper in the fall when you go to use your fireplace!

A Word of Warning

Don’t try to take the easy way out by using your household vacuum cleaner to remove the ashes from the firebox! You run the risk of ruining your vacuum cleaner so use a whisk broom and dustpan instead. In addition, the average household vacuum cleaner does not have the proper filter to prevent soot “blow-back” into the room. This blow-back may create a sooty mess on your carpeting, furniture, walls and window coverings. Even a Shop-Vac has the potential for creating blow-back. Professional chimney sweeps use industrial vacuums with special HEPA filters specifically designed to contain the fine particulates of soot.

The Best Solution

Of course, the easiest way to clean out your fireplace is to call your chimney sweep who’ll take care of that nasty chore for you as part of sweeping your chimney! In addition, your chimney will get a thorough inspection, inside and out, to make sure that it’s ready for the next burning season. The bonus is that we offer a discount during the spring and summer, so call Swede Chimney Sweep today at 858-573-1672. Check us out at www.swedesweep.com for additional information.