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When most people think of chimneys, they think of fireplaces. For thousands of years, humans have gathered around the open fire for a sense of safety and community, and the fireplace is still the focus of family living in many homes, especially around the holidays.

But in spite of all the glowing aesthetics, there are some practical considerations. When you're dealing with an element as dangerous as fire, knowledge is power. Please read on to learn how to make your fireplace both safer and more enjoyable.

Let's start with a quick anatomy lesson, and a brief explanation of common terms:

Fireplaces come in two general types: masonry fireplaces and factory built (prefab) fireplaces. To figure out which you have will take only a moment of detective work on your part. A masonry fireplace has a firebox built of individual generally yellowish firebrick, a brick chimney above the roof, and if you look up past the damper you will see a roughly pyramid shaped affair also built of brick. A prefab fireplace generally has a firebox of cast refractory panels, and usually some metal is visible in the room all around the firebox. If you look up past the damper, you will see a round metal chimney. And above the roof is more round metal chimney, sometimes surrounded by a simulated brick housing.

Although similar, there are some important differences which we discuss below.

MASONRY FIREPLACES - Some Special Considerations
Masonry fireplaces, built of bricks, blocks or stone and mortar, are massive structures often weighing between 6 and 7 tons! They are aesthetically pleasing, long lasting, and add real value to your home. With a little care and periodic maintenance they can give you a lifetime of enjoyment.

Masonry fireplaces require an extensive footing for support or they will often shift and crack, allowing the fire to escape to nearby combustibles. You should always keep an eye out for any signs of settling or movement. Inside the firebox, where the facing material meets the firebrick, is one weak spot where this settling often first appears. You can keep settling problems to a minimum by directing downspouts away from the fireplace and by sloping the ground around the fireplace so that water runs away from the structure.

Although masonry is quite durable, and in fact is often seen as indestructible, this is not the case, especially for chimneys. While the rest of the brick on the house receives some protection from the eave, the chimney is vulnerable to every raindrop and freeze/thaw cycle. A quality chimney cover, keeping the crown in good repair, and a waterproofing treatment, are great ways to avoid expensive repairs or rebuilding. See the section on waterproofing for a more detailed explanation.

The firebox of course takes the brunt of the fire's heat and it requires some special attention. The firebrick can take the heat pretty well, but over time the joints will fail from the constant expansion and contraction. In addition, refractory mortar is specified and seldom used. In a fireplace without a chimney cover, the rain water will pool on the smoke shelf, mix with the soot behind the damper, and form an acidic slurry that can destroy the mortar joints. Keeping these joints in good repair with a high temperature refractory mortar will help ensure the fire is contained.

The tile liners used in most masonry fireplaces are fine as long as the fireplace is properly maintained and not exposed to chimney fires. One good chimney fire will usually crack these tiles, rendering them ineffective. The general rule of thumb is that a masonry fireplace should be swept before 1/8" of soot accumulates. If you experience a chimney fire, it is very important to have the chimney swept and inspected before you use it again. Check out our information on Chimney Fires and Liners for further information.

Unlike prefabricated fireplaces, a masonry fireplace is built on site brick by brick, giving the mason ultimate control of the final product. This results in a wide range of masonry fireplaces available. With proper care and maintenance, Most masonry fireplaces can provide you with many peaceful, relaxing hours.

Prefabricated Fireplaces
​Factory built, or prefabricated fireplaces, are relative newcomers to the fireplace scene. Unlike traditional masonry fireplaces, most factory built fireplaces are metal, and come from the factory as complete units with a firebox, a specific chimney system, and all miscellaneous parts. With proper installation and maintenance, they can give years of service, but there are some special considerations:

1. The factory-built fireplace and chimney are a complete system, engineered to work together. Both units (fireplace and chimney), undergo testing together, then are listed specifically for use with each other.​
2. The installation instructions must be followed exactly, especially the specified clearances from the firebox and chimney to any combustible materials. Most manufacturers require no less than 2" of air space between the chimney components and all wood framing. If you are installing a new unit be sure you strictly adhere to these clearance instructions. If you already have a unit installed it is very important you check these clearances wherever possible. Any wood that is too close to the chimney will undergo a process called pyrolysis and even catch fire at temperatures as low as 200 degrees. Most of the units inspected by chimney professionals are improperly installed, and a trip to the attic to check clearances is definitely time well spent! Inspecting the firebox clearances is more challenging.
3. Most factory built fireplaces are tested and listed as decorative heating appliances and will not withstand excessively heavy use. Although they are tested to U.L. standards, severe over-firing and chimney fires will often badly damage these units. Regular yearly maintenance and careful monitoring can assure a safe enjoyable system.
4. Many prefab chimneys, especially older units with an imitation brick housing above the roof, seem to be a preferred nesting site for birds in many areas. It is not unusual for chimney sweeps to remove buckets of nesting material from these chimneys. This nesting can catch fire or block critical air passageways between layers of metal chimney pipe, causing the chimney to overheat. Both scenarios routinely cause house fires. Most aftermarket chimney covers are insufficient and can often make the problem worse. A careful screening of all potential nesting areas with the proper sized screening may be in order.
5. Finally, prefab fireplace systems eventually wear out. Models go out of production and manufacturers go out of business. Keep a close eye on an aging unit, and be prepared to send ole faithful to the great recycling plant in the sky before she fails completely.

Proper care and maintenance of your chimneys, woodstoves, and fireplaces can help protect you from unnecessary fires and carbon monoxide poisonings. We always recommend hiring a CSIA Certified Chimney Sweep®. You should also consider asking the following questions before allowing someone to service your home:

1. Can they provide references?
2. Does the company or individual carry a valid business liability insurance policy to protect your home and furnishings against accidents?
3. Does the company ensure that a CSIA Certified Chimney Sweep® will be on the job site?​​​​

You are also encouraged to look at any trusted review websites or business organizations in your area as well.To ensure that homeowners receive a certified sweep at every job, all chimney sweeping companies promoting themselves as "CSIA Certified" or displaying the CSIA Certified Sweep logo are required to have a CSIA Certified Chimney Sweep sign off on every job. To locate one of the more than 1,800 active CSIA Certified Chimney Sweeps across North America, please use the CSIA Certified Professional Locator.​

IMPORTANT: Just because a chimney sweep or company might say they are "certified", include the word "certified" in their title or advertising, or have great reviews on a consumer website, this might not mean they are well-suited for the job. Check out this blog post ​on how to ensure you're hiring the best person to keep your family safe from potential chimney fires or carbon monoxide intrusion.

Here are some simple scientific fundamentals to explain how and why a chimney works. This page should make it easier to understand how a CSIA Certified Chimney Sweep® can diagnose smoking or odor problems with your chimney.

Your House as a System

Even though you can't see it, the air in your house is in constant motion. In general, airflow tries to flow out of your house in the upper parts and replacement air tries to flow into your house in the lower parts of your house. Thinking of your house as a system makes it easy to understand the reasons for that airflow. Many changing factors, including: stack effect, wind loading, interior mechanical systems, and fuel-burning appliances such as furnaces, fireplaces, wood stoves and water heaters influence a home's airflow. 

Homes built or renovated in the past 25 years are more airtight than older homes. This makes it much more difficult for replacement air to enter the home. As the saying goes, “hot air rises”, and so does the warm air in your home. 

When the warm air rises to the upper areas of your home, it's called the stack effect. That trapped air forces its way out - even through very small openings such as recessed light fixtures and window frames. At the same time replacement air is trying to enter in the lower part of the building to make up for the escaping air.  

Somewhere in your house, amid all this airflow, is the Neutral Pressure Plane (NPP). Above this theoretical plane, the air pressure is slightly greater than the outdoor air pressure and it tries to force its way out of the house. Below the plane, it is slightly negative and the house is trying to draw air in from the outside. The location of the NPP changes in response to changing conditions. The factors that affect airflow in the house also influence the level of the Neutral Pressure Plane.  

Anytime a fireplace or fuel-fired heating appliance (except direct vent) is below the Neutral Pressure Plane, air will tend to flow into the house through the chimney or vent. A common example of this is found in homes with two fireplaces, one below the other. As the upper level fireplace uses air for combustion and chimney flow, it depressurizes that level slightly causing air to flow upwards from the lower level. Since the lower level fireplace is below the NPP, it draws air into the basement through the chimney. Unfortunately, since those two flues generally exit the chimney close to each other, the replacement air can contain some smoke from the fireplace above and it can pick up unpleasant chimney odors as it passes down the chimney flue. 

Wind-loading is the effect on interior house pressures caused by the wind. When wind strikes a building, it creates high pressure on the side that it hits and low pressure on the downwind side. Any open windows or doors on the windward side will help to pressurize the house, increasing chimney draft. However, openings on the downwind (leeward) side will depressurize the house and increase the likeliness of backdrafting from chimneys or vents. Backdrafting is a reversal of the airflow in which the smoke is coming into the house instead of going up the chimney.  

Interior mechanical devices such as clothes dryers, kitchen fans, bathroom fans, attic fans and central vacuums can also create depressurization by removing large volumes of air from the house. The result is often negative pressure in the area of a fireplace, woodstove, or other fuel-fired heating appliance making it difficult for natural draft chimneys to function as intended. Another common mechanical system that removes air from the house is a forced-air furnace. Many such systems are out-of-balance due to leaks in the ducts. Leaky supply ducts force air into the attic or crawlspace. Leaky return ducts draw air from the basement or other areas they pass through. 

Furnaces, water-heaters, fireplaces and woodstoves are examples of fuel-burning appliances that need large volumes of air for combustion. Unless they are specifically equipped to draw air in from outside the house, such as direct vent appliances, operating them can reduce the inside air pressure. There are a variety of mechanical devices on the market that help provide the necessary replacement air to balance the air pressure needs of your house system. 

Draft and Flow
Although most people don't realize it, the air moving up your chimney works under the same set of physical principles as water flowing in a hose or pipe. When a fireplace chimney is full of hot air, it actually pulls air through the firebox. This pulling effect is called draft and it corresponds to the amount of pressure in a water hose - the only difference is that the air pressure is negative and the water pressure is positive (think of using a straw to drink with instead of to blow bubbles). Thus, chimneys are negative pressure systems.

Increasing the draft in your chimney is like opening the faucet wider on the hose. The simplest way to increase the draft in your chimney is to burn the fire hotter - hotter air is lighter, so it has more pull. Another way to get more draft is to increase the height of your chimney - except when the chimney is already so tall that frictional forces negate the effect of the extra height. ​ Given the same amount of pressure, a larger pipe can carry a greater volume of water than a smaller one. The same is true for chimneys - with the same amount of draft (pressure) a larger flue will exhaust more smoke from your fireplace than a smaller one. Similar to how a water hose can be kinked or plugged, the airflow in your chimney can have a restriction that slows down the smoke flowing up the chimney.

​Poor flow in a chimney can result from: excessive creosote deposits, closed or plugged dampers, improper construction, structural damage or even a dirty chimney cap. In fact, having a plugged-up chimney cap at the end of your chimney is like having a closed nozzle at the end of a hose - preventing airflow through the chimney. Your CSIA Certified Chimney Sweep can check your chimney and recommend any corrective action needed for proper draft and flow.

A flue lining in a masonry chimney is defined as "A clay, ceramic, or metal conduit installed inside of a chimney, intended to contain the combustion products, direct them to the outside atmosphere, and protect the chimney walls from heat and corrosion."

​Although building codes vary from one state or locality to another, the installation of flue lining has been recommended since the early part of this century, and indeed most fire codes now mandate liners.

In the 1940's and again in the 1980's, masonry chimneys were tested by the National Bureau or Standards for durability due to rising concerns about their performance and safety. The tests revealed that unlined chimneys were so unsafe that researchers characterized building a chimney without a liner as "little less than criminal".

Chimney liners serve three main functions:

1. Protecting the house from heat transfer to combustibles. In the NBS tests, unlined chimneys allowed heat to move through the chimney so rapidly that the adjacent woodwork caught fire in only 3 1/2 hours.
2. Protecting the masonry from the corrosive byproducts of combustion. In the tests it was determined that if the flue gases were allowed to penetrate to the brick and mortar, the result would be a reduction in the usable life of the chimney. The flue gases are acidic in nature and literally eat away at the mortar joints from inside the chimney. As the mortar joints erode, heat transfers more rapidly to the nearby combustibles and dangerous gases such as carbon monoxide can leak into the living areas of the home.
3. Providing a correctly sized flue for optimum efficiency of appliances. Modern wood stoves and gas or oil furnaces require a correctly sized flue to perform properly. The chimney is responsible for not only allowing the products of combustion a passage out of the house, but the draft generated by the chimney also supplies the combustion air to the appliance. An incorrectly sized liner can lead to excessive creosote buildup in wood-burning stoves, and the production of carbon monoxide with conventional fuels.

Types of chimney liners:

• Clay tiles are the most common type of masonry chimney liners.
  • Advantages: They are inexpensive, readily available, and perform quite well for open fireplace chimneys that are properly maintained.
  • Disadvantages:  They cannot rapidly absorb and evenly distribute heat during the rapid temperature rise that occurs during a chimney fire, causing the flue tiles to crack and split apart (see the video below). The second disadvantage is that tiles cannot adequately contain the liquid combustion byproducts produced by modern gas appliances.​
• Metal chimney liners, usually of stainless steel or aluminum, are primarily used to upgrade and repair existing chimneys.
  • Advantages:  If properly installed and maintained, metal chimney liners are extremely safe and durable. Stainless steel is suitable for wood-burning, gas, or oil appliances, while the aluminum is an inexpensive alternative for certain medium efficiency gas applications only. It is usually required that high temperature insulation be used in conjunction with the liners for safety and performance considerations.
  • Disadvantage: Considerably more expensive than clay flue liners.
  • ​​National Chimney offers a line of metal chimney liners that have been accepted by CSIA as safe for home use when properly installed. 
• Cast-in-place chimney liners are lightweight, cement like products that are installed inside the chimney forming a smooth, seamless, insulated passageway for the flue gasses.
  • Advantage: They can improve the structural integrity of aging chimneys, and are permanent liners suitable for all fuels.
  • Disadvantage: Challenging installation and could be cost prohibitive.

Considering the dangers of old unlined or damaged chimneys, and the many cost effective options now available to make these chimneys safe components of the home heating system, we encourage you to have your chimney professionally inspected by a local CSIA Certified Chimney Sweep an an annual basis to be sure it meets modern safety standards.

An annual chimney inspection performed by a qualified professional can help prevent carbon monoxide intrusion and chimney fires. These inspections can also identify potential system issues to address them before they become costly. ​ ​

Many agencies and organizations now recognize the importance of annual heating system inspection and maintenance in keeping “the silent killer” at bay. ​

​A well-tuned furnace or boiler will operate efficiently and produce a warm and comfortable home. An overlooked heating system can produce death and heartbreak.

Considering the risks involved when heating systems are neglected - and the benefits of having them properly maintained - it is wise to have your chimneys checked annually by a CSIA Certified Chimney Sweep and swept or repaired as needed.

Gas Venting Basics
Most homeowners are aware of the need for chimney cleaning and inspection if they own a wood-burning stove or regularly use their fireplace, but many don't realize that a gas heating appliance-whether it is a furnace, boiler or even a hot water heater-also relies on the chimney for proper venting of the exhaust.

​Appliances fueled by natural gas or propane may not produce the visible soot that appliances burning other fuels do, but they can deposit corrosive substances in your chimney. In many cases, these acids may wreak havoc on your chimney without producing any external symptoms until the problem has become dangerous or expensive to repair.

The Problems
The problems lie with the modern higher efficiency appliances. These appliances gain their higher efficiency by extracting the heat that used to be sent up the chimney and delivering it to your home instead. No one wants to waste heat up the chimney, but a certain amount of heat is necessary in order to provide the draft that makes the venting system work, and to keep the chimney walls warm enough to prevent condensation of the flue gases. If the flue temperature becomes too low, as is often the case with modern appliances, two separate but interrelated problems- incomplete combustion and water condensation- can occur.

Incomplete combustion:
The chimney is responsible not only for simply letting the combustion byproducts passively escape up the flue, but it also generates draft that actively pulls combustion air into the appliance. In fact, burning one cubic foot of natural gas requires 10 cubic feet of air to provide enough oxygen for complete combustion. If the chimney is too cool to create adequate draft, thereby not providing enough combustion air, not only does efficiency suffer, but the appliance can produce carbon monoxide, and this carbon monoxide is less likely to be safely exhausted from a chimney with a weak draft signal.

Condensation:
The second and most obvious problem from cool chimney temperatures is the condensation of water vapor inside your chimney. As odd as it may seem, the combustion of any hydrocarbon-and gas is a hydrocarbon-results mainly in carbon dioxide and water vapor. In fact, the average furnace puts about 1 1/2 gallons of water into your chimney every hour! The high stack temperatures of the older inefficient furnaces kept this moisture from condensing inside the chimney, and it was often visible as steam escaping from the chimney top. Because the newer high efficiency furnaces now steal this extra heat from the chimney, all this water now often condenses inside the cooler flue.

The problem becomes even more complicated however because this water is also usually highly acidic and corrosive. The air used for combustion is generally contaminated with not only normal air pollution, but often with household cleaning products, especially chlorine from bleach. If the chimney was previously used to vent coal or oil there are most likely also sulfur deposits left inside too. So now not only do you have a gallon or more of water an hour in your chimney, you now have a gallon or more of dilute hydrochloric or sulfuric acid eating away at the mortar and brick of your chimney from the inside!

The situation is aggravated by cold exterior chimneys and long runs of connector pipe between the furnace and the chimney. Although your chimney may be suffering from an improper heating/venting match without producing any visible symptoms, sometimes the excess moisture produced causes visible results.

Any of the following symptoms could point to a venting system problem.

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• Damp patches on interior walls or exterior walls
• Peeling wallpaper
• Blistered paint
• Stains on the ceiling around the chimney
• White stains (efflorescence) on the outside of the masonry chimney
• Eroded mortar joints
• Crumbling bricks

Eventually corrosion caused by this acidic water condensing inside the flue may cause the liner, mortar, and brickwork to flake and crumble. Chimney sweeps often find this debris creating blockages in the flue, potentially exposing the occupants of the home to carbon monoxide and other dangerous combustion byproducts, a situation not to be taken lightly.

Solutions

The first step is to have the chimney/venting system evaluated by a competent Certified Chimney Sweep tm, someone who understands the relationships between furnace and chimney type. A qualified sweep can offer advice and recommend measures to make your entire system function safely and efficiently.

​
If a problem is found, the solutions often involve installing a correctly sized, insulated liner, and/or reworking the connector pipe between furnace and chimney. These upgrades are designed to resize the flue for better draft, minimize the condensation, and contain the acidic byproducts within the liner to protect the surrounding masonry. (See our page on liners for more information)

​
A few dollars spent on corrective measures could save thousands in expensive chimney repair down the road, and will help protect your home and family.

Most homeowners are aware of the need for chimney cleaning and inspection if they own a wood-burning stove or regularly use their fireplace, but many don't realize that oil heating appliances also relies on the chimney for proper venting of the exhaust. That chimney system also requires annual inspections for efficient operation.

Maybe you’re in the market for a new oil-fired appliance or your chimney or oil service technician has recommended that you have your chimney relined before making a change to your appliance. CSIA has more information about relining your oil-fired appliance chimney available.

A common misconception is that your oil service technician takes care of the chimney. The reality is that the oil burner company may shovel out the base of a brick chimney and they may brush out the connector pipes, but likely will not clean the chimney system.

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Annual servicing of your oil-fired appliance chimney includes going to the roof and inspecting the interior as well as the exterior masonry (if applicable), flashing, chimney cap, etc.

The chimney is one of the most taken-for-granted parts of a home. Typically it tends to receive neither the attention nor the concern usually accorded other household service systems. The fact that chimneys may do their job reasonably well, even when abused or neglected, contributes to this atmosphere of indifference.​Chimneys are far from the passive black holes that most people assume them to be. They perform several vital functions, and their simple appearance misrepresents their complex construction and performance requirements. A chimney deteriorated by constant exposure to the weather can be a potential safety hazard. Weather-damaged lining systems, flue obstructions and loose masonry materials all present a threat to residents. Regular chimney maintenance is essential to prevent damage, deterioration and future high-cost chimney repairs.

Masonry Chimneys
A masonry chimney is constructed of a variety of masonry and metal materials, including brick, mortar, concrete, concrete block, stone, flue tile, steel and cast iron. All masonry chimneys contain combinations of, or possibly all of, these materials, most of which are adversely affected by direct contact with water or water penetration.

​Water Penetration
All masonry chimney construction materials, except stone, will suffer accelerated deterioration as a result of prolonged contact with water. Masonry materials deteriorate quickly when exposed to the freeze/thaw process, in which moisture that has penetrated the materials periodically freezes and expands causing undue stress. Water in the chimney also causes rust in steel and cast iron, weakening or destroying the metal parts.

Note: While most stone is not affected by water penetration, large amounts of mortar are required to bond the stone together properly. Therefore, a stone chimney – just like a brick chimney – should be protected from the effects of water penetration.Water penetration can cause interior and exterior damage to your home and masonry chimney including:

• Rusted damper assemblies
• Deteriorated metal or masonry firebox assemblies
• Rusted fireplace accessories and glass doors
• Rotting adjacent wood and ruined wall coverings
• Water stained walls and ceiling
• Clogged clean out area
• Deteriorated central heating system
• Stained chimney exterior
• Decayed exterior mortar
• Cracked or deteriorated flue lining system
• Collapsed hearth support
• Tilted or collapsed chimney structure
• Chimney settlement

In addition, when water mixes with creosote in a wood burning chimney system, it will generate a highly disagreeable odor that can permeate a home.
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Preventing Water Damage
Chimney caps, also called rain covers, are probably the most inexpensive preventive measure that a homeowner can employ to prevent water penetration and damage to the chimney. Chimney caps have long been recognized as an important chimney safety and damage prevention component. Underwriters Laboratories (UL) specifies that any chimney lining system that is to be listed to their test standard must include a chimney cap.

Chimneys have one or more large openings (flues) at the top that can collect rainwater and funnel it directly to the chimney interior. A commonly-sized flue has the potential to allow large amounts of rain or snow into the chimney during just one winter when freeze/thaw cycles are common.

Chimney caps also provide other benefits. A strong, well-designed cap will prevent birds and animals from entering and nesting in the chimney. Caps also function as spark arrestors, preventing sparks from landing on the roof or other nearby combustible material.

A chimney cap should be easily removable to facilitate inspection and cleaning. For a long and effective service lifetime, a cap should be constructed of sturdy, durable and corrosion resistant material. Caps may be designed to cover a single flue, multiple flues, a large portion of the chimney or the entire chimney top. A full coverage chimney cap usually represents a larger initial investment. However, it is probably the best investment for long-term protection because of its ability to protect the entire chimney crown.

Repair or Replace a Damaged Chimney Crown

The chimney crown (also referred to as the chimney wash) is the top element of a masonry chimney. It covers and seals the top of the chimney from the flue liner to the chimney edge. The crown should provide a downward slope that will direct the water from the flue to the edge of the crown. The overhanging drip edge, by directing the run-off from the crown away from the chimney, helps prevent erosion of the brick and mortar in the chimney’s vertical surfaces.

Most masonry chimneys are built with an inadequate crown constructed from common mortar mix that will crack, chip, or deteriorate from weather exposure. A proper chimney crown should be constructed of a Portland cement-based mixture and cast or formed so it provides an overhang projecting beyond all sides of the chimney by a minimum of two inches. The flue liner tile should also project above the crown a minimum of two inches.

Repair Deteriorated Mortar Joints

Deteriorated mortar joints on the chimneys exterior are entry spots for water. Proper mortar joints have no gaps or missing mortar and are shaped in a way that directs water out of the joint. When mortar deteriorates from exposure to weather, it becomes much more absorbent. A common repair for deteriorated mortar joints is called repointing. In this process, the existing mortar joint is cut to an appropriate depth and the joint is repacked with new mortar. The joint is then cut to form a concave surface that will direct water out of the joint. A good repointing job, using proper materials, will give the chimney a much longer life span, and often will enhance its appearance.

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Repair or Replace Flashing

Flashing is the seal between the roofing material and the chimney. Flashing prevents rainwater or snow melt from running down the chimney into living spaces where it can damage ceilings and walls and cause rot in rafters. The flashing is the expansion joint between two dissimilar materials. It is designed to allow both the roof and the chimney to expand and contract at their own rates without breaking the waterproof seal in either area.

Install a Cricket to Stop or Prevent Leaks

If the chimney is located on the low side of the roof where water run-off is directed against the chimney, the installation of a cricket will afford additional protection against water leaking into the home. A cricket is a water deflector that serves to direct rainwater away from the chimney. Crickets are recommended on chimneys more than 30-inches wide and they are especially important on steep roofs.

Waterproof Your Chimney

Most masonry materials are porous and will absorb large amounts of water. Common brick is like a sponge, absorbing water and wicking moisture to the chimney interior. Defective mortar joints or the use of improper mortar or brick can greatly increase the tendency to absorb and convey water to the interior of the masonry chimney. 

Several products have been developed specifically for use as waterproofing agents on masonry chimneys. These formulas are 100% vapor permeable, which means that they allow the chimney to breathe. Therefore, water that has penetrated and the vapors produced when the chimney dries out or the water vapors produced during use are allowed to escape, while the waterproofing agent prevents water from entering from the outside. These products usually have a five- to ten-year warranty. Paint or clear sealers should never be used as a waterproofing agent because they will trap water vapors and moisture inside the chimney causing further deterioration.

Waterproofing is a preventive measure. When damage or deterioration (gaps, voids, cracks, missing mortar, etc.) already exists in a masonry structure, the chimney should be repaired before the waterproofing agent is applied. The chimney exterior may also need to be cleaned before the waterproofing material is applied.

Your chimney–and the flue that lines it–adds architectural interest to your home, but its’ real function is to carry dangerous flue gases from your fireplace, wood stove or furnace safely out of your home. As you relax in front of your fireplace or bask in the warmth of your wood stove, the last thing you are likely to be thinking about is the condition of your chimney. However, if you don’t give some thought to it before you light those winter fires, your enjoyment may be very short-lived.

Why?

Dirty chimneys can cause chimney fires, which damage structures, destroy homes and injure or kill people. ​Indications of a chimney fire have been described as creating:

• loud cracking and popping noise
• a lot of dense smoke, and
• an intense, hot smell

​Chimney fires can burn explosively – noisy and dramatic enough to be detected by neighbors or people passing by. Flames or dense smoke may shoot from the top of the chimney. Homeowners report being startled by a low rumbling sound that reminds them of a freight train or a low flying airplane. However, those are only the chimney fires you know about.

The best way to prevent a chimney fire is to have an annual inspection performed by a CSIA Certified Chimney Sweep.

The Majority of Chimney Fires Go Undetected

​Slow-burning chimney fires don’t get enough air or have fuel to be dramatic or visible and they often go undetected until a later chimney inspection, but, the temperatures they reach are very high and can cause as much damage to the chimney structure – and nearby combustible parts of the house – as their more spectacular cousins.

Creosote & Chimney Fires: What You Must Know

Fireplaces and wood stoves are designed to safely contain wood-fuel fires, while providing heat for a home. The chimneys that serve them have the job of expelling the by-products of combustion – the substances produced when wood burns. These include smoke, water vapor, gases, unburned wood particles, hydrocarbon, tar fog and assorted minerals. As these substances exit the fireplace or wood stove, and flow up into the relatively cooler chimney, condensation occurs. The resulting residue that sticks to the inner walls of the chimney is called creosote.  

Creosote is a black or brown residue that can be crusty and flaky…tar-like, drippy and sticky…or shiny and hardened. All forms are highly combustible. If it builds up in sufficient quantities – and the internal flue temperature is high enough – the result could be a chimney fire.  

Conditions that encourage the buildup of creosote:

• restricted air supply
• unseasoned wood
• cooler than normal chimney temperatures

Air supply may be restricted by closing the glass doors, by failing to open the damper wide enough, and the lack of sufficient make-up air to move heated smoke up the chimney rapidly (the longer the smoke’s “residence time” in the flue, the more likely is it that creosote will form). A wood stove’s air supply can be limited by closing down the stove damper or air inlets too soon or too much. Burning unseasoned wood – because so much energy is used initially just to drive off the water trapped in the cells of the logs– keeps the resulting smoke cooler, than if seasoned wood is used. In the case of wood stoves, overloading the firebox with wood in an attempt to get a longer burn time also contributes to creosote buildup.

The Effect of a Chimney Fire on Your Chimney

Masonry Chimneys

When a chimney fire occurs in a masonry chimney – whether the flue is an older, unlined type or tile lined to meet current safety codes – the high temperatures at which they burn (around 2000°F) can “melt mortar, crack tiles, cause liners to collapse and damage the outer masonry material”.  Most often, thermal shock occurs and tiles crack and mortar is displaced, which provides a pathway for flames to reach the combustible wood frame of the house. This event is extremely dangerous, call 911 immediately.

Prefabricated, factory-built, metal chimneys

To be installed in most jurisdictions in the United States, factory built, metal chimneys that are designed to vent wood burning stoves or prefabricated metal fireplaces must pass special tests. Most tests require the chimney to withstand flue temperatures up to 2100°F – without sustaining damage. Under chimney fire conditions, damage to these systems still may occur. When prefabricated, factory-built metal chimneys are damaged by a chimney fire, they should no longer be used and must be replaced.  

Special Effects on Wood Stoves

Wood stoves are made to contain hot fires. The connector pipes that run from the stove to the chimney are another matter. They cannot withstand the high temperatures produced during a chimney fire and can warp, buckle and even separate from the vibrations created by air turbulence during a fire. If damaged by a chimney fire, they must be replaced. 

Nine Signs that You’ve Had a Chimney Fire 

Since a chimney, damaged by a chimney fire, can endanger a home and its’ occupants and a chimney fire can occur without anyone being aware of them it’s important to have your chimney regularly inspected by a CSIA Certified Chimney Sweep. Here are the signs that a professional chimney sweep looks for:

• “Puffy” or “honey combed” creosote
• Warped metal of the damper, metal smoke chamber connector pipe or factory-built metal chimney
• Cracked or collapsed flue tiles, or tiles with large chunks missing
• Discolored and/or distorted rain cap
• Heat-damaged TV antenna attached to the chimney
• Creosote flakes and pieces found on the roof or ground
• Roofing material damaged from hot creosote
• Cracks in exterior masonry
• Evidence of smoke escaping through mortar joints of masonry or tile liners​

If you think a chimney fire has occurred, call a CSIA Certified Chimney Sweep for a professional evaluation. If your suspicions are confirmed, a certified sweep will be able to make recommendations about how to bring the system back into compliance with safety standards. Depending on the situation, you might need a few flue tiles replaced, a new liner system installed or an entire chimney rebuilt. Each situation is unique and will dictate its own solution.  

Proper Maintenance

Clean chimneys don’t catch fire. Make sure a CSIA Certified Chimney Sweep® inspects your solid fuel venting system annually, and sweeps and repairs it whenever needed. Your sweep may have other maintenance recommendations depending on how you use your fireplace or stove. CSIA recommends that you call on CSIA Certified Chimney Sweeps®, since they are regularly tested on their understanding of the complexities of chimney and venting systems.  

Quality, well seasoned firewood will help your wood stove or fireplace burn cleaner and more efficiently, while green or wet wood can cause smoking problems, odor problems, rapid creosote buildup and possibly even dangerous chimney fires.

Seasoned Wood
All firewood contains water. Freshly cut wood can be up to 45% water, while well seasoned firewood generally has a 20-25% moisture content. Well seasoned firewood is easier to start, produces more heat, and burns cleaner. The important thing to remember is that the water must be gone before the wood will burn. If your wood is cut 6 months to a year in advance and properly stored, the sun and wind will do the job for free. If you try to burn green wood, the heat produced by combustion must dry the wood before it will burn, using up a large percentage of the available energy in the process. This results in less heat delivered to your home, and literally gallons of acidic water deposited in your chimney.

Wood is composed of bundles of microscopic tubes that were used to transport water from the roots of the tree to the leaves. These tubes will stay full of water for years even after a tree is dead. This is why it is so important to have your firewood cut to length for 6 months or more before you burn it, it gives this water a chance to evaporate since the tube ends are finally open and the water only has to migrate a foot or two to escape. Splitting the wood helps too by exposing more surface area to the sun and wind, but cutting the wood to shorter lengths is of primary importance.There are a few things you can look for to see if the wood you intend to purchase is seasoned or not. Well seasoned firewood generally has darkened ends with cracks or splits visible, it is relatively lightweight, and makes a clear "clunk" when two pieces are beat together. Green wood on the other hand is very heavy, the ends look fresher, and it tends to make a dull "thud" when struck. These clues can fool you however, and by far the best way to be sure you have good wood when you need it is to buy your wood the spring before you intend to burn it and store it properly.

​Storing Firewood

Even well seasoned firewood can be ruined by bad storage. Exposed to constant rain or covered in snow, wood will reabsorb large amounts of water, making it unfit to burn and causing it to rot before it can be used. Wood should be stored off the ground if possible and protected from excess moisture when weather threatens.

The ideal situation is a wood shed, where there is a roof but open or loose sides for plenty of air circulation to promote drying. Next best would be to keep the wood pile in a sunny location and cover it on rainy or snowy days, being sure to remove the covering during fair weather to allow air movement and to avoid trapping ground moisture under the covering. Also don't forget that your woodpile also looks like heaven to termites, so it's best to only keep a week or so worth of wood near the house in easy reach. With proper storage you can turn even the greenest wood into great firewood in 6 months or a year, and it can be expected to last 3 or 4 years if necessary.

Buying Firewood

Firewood is generally sold by volume, the most common measure being the cord. Other terms often employed are face cord, rick, or often just a truckload. A standard cord of firewood is 128 cubic feet of wood, generally measured as a pile 8 feet long by 4 feet tall by 4 feet deep. A face cord is also 8 feet long by 4 feet tall, but it is only as deep as the wood is cut, so a face cord of 16" wood actually is only 1/3 of a cord, 24" wood yields 1/2 of a cord, and so on.

Webster defines a rick simply as a pile, and truck sizes obviously vary tremendously, so it is very important that you get all of this straight with the seller before agreeing on a price; there is much room for misunderstanding. It is best to have your wood storage area set up in standard 4 or 8 foot increments, pay the wood seller the extra few dollars often charged to stack the wood, and warn him before he arrives that you will cheerfully pay only when the wood actually measures up to an agreed upon amount. 

Another thought concerning getting what you pay for is that although firewood is usually sold by volume, heat production is dependent on weight. Pound for pound, all wood has approximately the same BTU content, but a cord of seasoned hardwood weighs about twice as much as the same volume of softwood, and consequently contains almost twice as much potential heat. If the wood you are buying is not all hardwood, consider offering a little less in payment. 

Top Firewood Tips

• It is far more important that the fuel be dry as compared to the species.
• Do not burn any construction scraps of treated or painted wood, especially treated wood from decks or landscaping ties. The chemicals used can release dangerous amounts of arsenic and other very toxic compounds into your house.
• If the "seasoned wood" you bought turned out to be pretty green and you elected to try to burn it anyway, be sure to have the chimney checked more often than usual, you may build up creosote very quickly. You don't have to burn only premium hardwoods. Less dense woods like elm and even soft maple are abundant and make fine firewood as long as you're willing to make a few extra trips to the woodpile.
• If you have access to a variety of species, learn to manage your woodpile. Save the more dense fuel for the coldest months and use the "lighter" wood for kindling fires and during the spring or fall when you don't need as much heat.
• Many people also have questions about burning artificial logs. Convenience is their strong suit and in general they are fine when time is an issue and you want a quick fire without all the muss and fuss of natural firewood. Usually they should be burned only one at a time and only in an open fireplace. One should be careful about poking them and moving them around once they are burning since they may break up and the fire may get a bit out of control. Be sure to carefully read the directions on the package.

Wouldn’t it be great if there was a way to easily start a fire every time with less smoke? It’s possible, But you will have to discard your previous experience and approach this new method with an open mind. Most people learned the old “log cabin” style of building a fire with the smallest kindling at the bottom. You are about to learn the top-down method, which is exactly the opposite of what you were taught.

The top-down method works equally well in wood stoves, fireplaces and masonry heaters. In fact, the technique has been in use for hundreds of years with the large masonry heaters found all over Europe. It works just as well today as it did then.
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Start by placing the largest pieces of wood in the bottom of the fireplace or wood stove, with the ends at the front and back. Some wood stoves will have a deeper or wider firebox and this will certainly be a consideration when you’re cutting wood. Placing the wood with the ends at the front and back allows the air to mix well with the fuel instead of only hitting the broad side of the wood as it would if it were placed parallel to the opening.

​Some wood burners prefer to use hardwood for the bottom row and softer (though no less dry) wood near the top of their firebox. The real key is to make the kindling small enough to easily ignite on top of the pile. All of the wood should be dry, but this is especially critical of the wood at the top.

Once you have placed the bottom row, stack 4-5 smaller levels of wood on top of the first layer until your wood is stacked to about 1/2 of the height of the fireplace. At this point you will begin placing your kindling (the smallest pieces of wood). Again stack smaller and smaller pieces until there are simple wood shavings on top. If you wish to cheat a little you can place a crumpled up piece of newspaper on top. In any case, the stack should not go above the fireplace opening.
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The shavings at the top should be small enough to light with a single match. As the fire burns from the top to bottom, it will continue to ignite the wood below. This method is a “light it and you’re done” procedure. No more fiddling with larger pieces of wood falling on the struggling new fire. Notably, only a little smoke is created as the fire burns cleanly from the top of the stack. This brightly burning fire makes it less likely that the fireplace will smoke as it heats the chimney without the interference of loads of wood resting on top of it.

There’s a romance attached to wood stoves that folks don’t feel for their gas or oil furnaces. The reasons include economics, aesthetics, efficiency and environmental concerns. Today, wood stoves offer homeowners the promise of a heating system that’s independent of local utilities, plus the lure of cozy evenings cheered by gently flickering flames.

An Exit for the Smoke
If there’s a wood stove in your life (or in your future) and you already have a masonry fireplace in your home, you may want to use your fireplace’s chimney to vent your wood stove or wood burning fireplace insert. Such a choice would seem both sensible and economical. 

However, any heating system works best when all its parts are designed – at the outset – to work together. A furnace operates best when the flue size is carefully matched to the furnace capacity.  It is the same with a wood stove; it is the safest and most efficient when attached to a chimney whose flue size most closely matches the size of the vent pipe which connects the stove to the chimney.

Today’s Wood Stoves & Inserts

There are two types of wood stoves that can be connected to fireplace flues: freestanding stoves and fireplace inserts. These stoves can be vented into chimneys constructed of masonry or a factory-built metal system that’s been designed, tested and listed for use with wood burning appliances; they can also connect to an existing fireplace chimney, if the height and position of the stove’s flue collar permits it.

Since 1984, national codes and standards have dictated that a connector pipe extend from the outlet of the stove or insert, up through the fireplace damper, and to the first flue tile of the masonry chimney. Arguably the best installation option is installing a stainless steel liner from the top of the stove to the top of the chimney.  This method provides the most efficiency and is the easiest to sweep and inspect. 

Stoves & Inserts Connected to Fireplaces: A Different Equation

When installing an insert into a fireplace the size of an insert’s firebox is smaller than that of the masonry firebox, so the existing masonry flue may now be disproportionately large.  The chimney draft is created like a tornado, when a warm front meets a cold front. Venting into an oversized flue is like pouring a cup of hot water into a sink full of cold water. The cooler temperature causes the smoke to linger and even drop below the dew point and deposit large quantities of creosote on the chimney walls.

Creosote is a brown or black combustible deposit produced when smoke condenses. Creosote needs to be monitored and removed to help reduce the risk of chimney fire.  Smoke condenses inside both the firebox and smoke chamber and may produce a ceramic-like hard glaze of condensed creosote – which is hazardous, difficult and potentially expensive to clean and which damages masonry materials through the corrosive action of acids it contains.

By today’s standards the installation of a hearth stove or insert where the connector pipe does not extend to at least the first flue tile is not acceptable even if the manufacturer’s instructions don’t require it.  The best installation option is the installation a stainless steel liner from the top of the stove to the top of the chimney.  This method provides the most efficiency and is the easiest to sweep and inspect.  
This new chimney liner when sized correctly for the wood stove or insert is less likely to be a problem. In addition, it is an easy and economical way to extend the life of your chimney, since the new liner protects the existing structure from heat deterioration and acid-based smoke condensation.

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Operation & Maintenance

An approved wood stove-to-fireplace installation will help assure your safety. Annual inspections and sweeping of these systems by a CSIA Certified Chimney Sweep® will enhance their safety and efficiency.

The chimney swift is one of four regularly occurring species of swifts found in North America, the most common one found east of the Rockies. They have become accustomed to building their nests in chimneys as well as abandoned buildings and occasionally stone wells.

​Chimney swifts are protected by the federal Migratory Bird Treaty Act and cannot legally be removed from your chimney!

Adult chimney swifts are most commonly seen in flight, and usually in groups. When soaring, their long, scythe-shaped wings span about 12 1/2 inches, supporting a proportionately short body with a squared-off tail. The flickering, bat-like flight when flapping is due to short, massive wing bones. During this spectacular aerial ballet, swifts are most often patrolling the skies for mosquitoes and the other small flying insects that constitute the majority of their diet. A sharp chippering or ticking call accompanies the swifts' flight.

​At rest, an average 5-inch, .8-ounce adult is sooty gray to black with the throat slightly lighter or even silvery gray, in color. The sexes are identical in appearance. Both the claws and tail bristles are used to cling to rough vertical surfaces. Swifts are unable to perch or stand upright in passerine fashion

Chimney swifts winter in the Amazon Basin of Peru. They arrive in the continental United States in late March and are gone by early November. Nesting begins in May and can continue into August. Chimney swifts are usually single-brooded. The female normally lays three to five white eggs in a nest of twigs broken from the tips of tree branches, glued together with saliva and attached to inside wall of a chimney. Both sexes are involved in nest construction and alternate incubating the eggs for 18 to 19 days, when the young begin to hatch. Their parents catch flying insects on the wing to feed them until the birds fledge from the chimney about 30 days after hatching.

The hatchlings are pink, altricial and completely naked at birth. They have sharp claws, which enable them to cling to textured surfaces, Within a few days, black pinfeathers begin to appear. The young are able to climb, and they exhibit preening behavior even before their feathers emerge.

By the time they are 8 or 10 days old, the babies' feathers begin to unfurl. By 15 to 17 days of age, their eyes begin to open. Soon, most of the flight and body feathers will be unfurled, but the feathers around the face and head will stay in sheath for several days, giving then birds a frosty-faced appearance.

By the time chimney swifts are 21 days old, they will cling tightly to the nest or chimney wall, rear back, and flap their wings furiously until they are panting and out of breath. Twenty-eight to 30 days after hatching, young swifts will leave the safety of their chimney for their first flight.
Once an entire brood has fledged, they will fly with their parents in slow, noisy parades around the area of the nest site. The young will return frequently to the roost during the first few days, but will soon begin to visit other roosts in the area.

At the end of the breeding season, the swifts' communal instincts peak prior to fall migration. They congregate in flocks of hundreds and even thousands at suitable roost sites.

Although chimney swifts can withstand a few early cool snaps, they will usually ride south on the first major cloud front that blows through the fall.

Read the Migratory Bird Treaty