When the cold winter winds start blowing outside the talk about the warm crackle and glow of a wood fire in a fireplace inside your home is started - during Thanksgiving my father in law reminded me to make sure my fireplace is cleaned out before starting to use it this year. I said Ba-Humbug about these "dangers." But privately I wanted to know more so here's what I found out.

Safety First

If improperly installed, operated, or maintained, wood burning fireplaces are potential sources of house fires. Embers popping out of an unscreened fire or chimney fires from creosote build-up are just two of the hazards that can be avoided with proper use and care. Wood burning fireplaces can also negatively affect indoor quality - asthmatics, elderly or sick people might be suffering without knowing.

Smoke may smell good, but it’s not good for you.” Any smoke escaping from the firebox into the room means the fireplace isn’t operating properly. Also, since fires consume a large volume of air as they burn, it’s possible to create negative pressure in the home as air from outside is drawn indoors to replace the air consumed by the fire. If that “make-up” air is drawn back in through the flues of gas- or oil-burning furnaces and water heaters, it can also draw deadly flue gases, like carbon monoxide, back into the home. This is called “backdrafting” and is one reason all homes should be outfitted with working, well-maintained smoke and carbon monoxide alarms. 

 “Safety is the best reason to have a professional chimney sweep inspect, clean, and test any fireplace when you move into a home. While it is possible for homeowners to clean and maintain their own fireplaces and chimneys, it’s unlikely that they possess the requisite knowledge or experience to spot all potential problems during an inspection.”

Fireplace and Chimney Elements

Most wood-burning fireplaces are built of heavy masonry materials on solid foundations with masonry chimneys. Some are factory built and have special triple-wall, stainless steel chimneys.

One common masonry type is called a “Rumford” fireplace, after the 18th century British Count Rumford who developed the design. Rumford fireplaces were much better at removing smoke from a fireplace and heating a room than their predecessors. The design has stood the test of time – Rumford-inspired fireplaces even outperform some newer, modern design. 

A masonry fireplace’s firebox is built with special, heat-resistant firebrick, and the interior of the chimney is lined with heat-resistant, square clay tubes, called “tiles.” The visible parts of the chimney, hearth, and fireplace are typically made of non-combustible materials like standard brick, stone, or tile. The chimney is sometimes capped with a metal or stone slab to keep rain and snow out, as well as screen to keep birds  and animals out of the chimney. Eldridge says the screens serve another use, too: “The screen also acts as a spark arrester, containing any embers which happen to make it all the way up the chimney to the top.”

A chimney cap keeps rain, snow, birds, and animals from entering the chimney and keeps embers inside the chimney preventing potential fires

The Damper

What is that small lever at the top of your fireplace?

A small, cast-iron door, called a damper, is installed just over the fire, leading to the chimney, and is operated by an attached handle. The damper helps control the intensity of the fire by limiting airflow. It is closed while the fireplace is not in use and opened when a fire is lit. It can also be used to control how much air flows through the firebox to feed the fire, which helps regulate how intensely the fire burns. It’s common for fireplaces to have a screen or mesh guard, which keeps embers from popping into the room when a fire is burning. Sometimes fireplaces have glass doors, which should be left open when the fire is burning, but which can be closed when the fire is reduced to embers or when there is no fire burning, to reduce unwanted airflow up the chimney.

Many fireplaces will also have a raised fire grate, which elevates the fire to allow better airflow and combustion, and an ash-dump door on the floor of the firebox, both made of cast-iron. The ash dump allows cold ash to be swept into a chamber below the firebox, usually into an enclosed chamber in the fireplace foundation in the basement. There, the ash can be accessed by another small, tight-fitting metal door, where it can be removed without getting the finished living area dirty. 

The ash dump allows ash collection to happen in the basement, where the mess can be more easily contained.

While the masonry firebox is the most common type, some fireplaces are outfitted with special metal inserts to allow for more efficient, cleaner burning of wood. Many times inserts include fans which circulate air from the living area around the outside of a sealed firebox, making the fire a more efficient heater of living spaces. This makes a wood-burning fireplace work more like a wood stove.

How It Works

Before lighting a fire, the damper is opened to allow smoke and combustion gases to escape. Once the fire is lit, the extremely hot combustion gases begin to rise up the chimney by convection. At the same time, the fire is drawing air from the home for combustion. As the flame stabilizes, the hot, deadly combustion gases continue to be drawn up and out of the top of the chimney, drawing fresh air in for combustion at the same time.

The End of the Night. - is the fire OUT?

Once the fire dies and the ashes are completely cold, the damper is closed to avoid unwanted loss of heat from the home. Then the ashes can be cleaned from the firebox or delivered to the ash dump through a door in the floor of a masonry

Much make-up air is frigid air drawn in through cracks and gaps in the home, making the house feel cold and drafty. Installing a pipe between the outdoors and the fireplace to bring in make-up air directly avoids both the discomfort of air-infiltration through cracks and gaps and the potential danger of backdrafting due to insufficient available combustion air.

Fireplaces can be made somewhat safer and more efficient by installing glass doors. This adds a layer of protection while also more carefully controlling airflow to the fire. However, even a fireplace with glass doors has fairly poor heating efficiency. Installing a high-efficiency, EPA approved, metal fireplace insert makes the fireplace behave more like a wood stove.

North Shore Contractor Management knows that saving money from Wood Burning Stoves is a question on all homeowners minds. It's not as expensive or troublesome as you would think.

Part of the North Shore consultation is explaining the cost vs benefits of changing homes into more energy efficent dwellings. 

This way, a fireplace can be converted to become a cleaner, more efficient source of heat than a traditional fireplace and can save the homeowner money on heating bills.