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Maintaining Fireplaces and Chimneys

This homeowner’s guide to fireplaces and chimneys covers safety issues, inspection and cleaning, and the simple maintenance required to ensure years of safe enjoyment of your fireplace, wood stove, and chimney.


Most folks consider their fireplaces and chimneys to be indestructible parts of their home that require little or no maintenance. While masonry work is generally as close to maintenance-free as you can get, fireplaces and chimneys are more than just works of masonry: they are a part of your home’s heating system. They must effectively exhaust fumes from your fireplace, furnace and water heater. Relatively minor but regular maintenance efforts can help your chimney operate safely for an indefinite period of time. In the U.S., many people are poorly informed about the importance of basic chimney maintenance. This lack of understanding causes a substantial number of preventable deaths and injuries each year. Beyond the safety issue, neglect of chimneys leads to very expensive major repairs that would not be necessary if the chimney were properly maintained.

Threats Associated With Poor Chimney Maintenance

The three most serious problems that result from poorly maintained chimneys are carbon monoxide poisoning, chimney fires, and premature failure of the structure itself. Each of these problems is discussed below.

Carbon monoxide poisoning claims about 4,000 lives a year in the U.S., and a significant number of these deaths are the result of poorly maintained chimneys. In addition, about 10,000 people are made ill by lower levels of exposure to carbon monoxide. Carbon monoxide is a by-product of combustion. The less complete the burning (combustion), the more carbon monoxide is generated. Gas hot water heaters, gas and oil furnaces, fireplaces, and wood stoves all generate carbon monoxide. Cars also generate the deadly gas, with many deaths and illnesses coming from people warming up their cars in closed garages.

One of the reasons carbon monoxide is so deadly is that you generally can’t see or smell it: rarely do its victims have any warning. Low levels of poisoning tend to cause flu-like symptoms, so that people think they are just catching a cold. More advanced poisoning can cause vomiting and headaches and even death. Carbon monoxide is deadly because it tricks the body into thinking it is oxygen. The body actually prefers carbon monoxide, choosing it over oxygen when both are present in the atmosphere. Once in the body, carbon monoxide is given the same red carpet treatment that is accorded life-supporting oxygen. It goes everywhere in the body, including (and especially) the brain. Children, in particular, are quite susceptible to brain damage after relatively low levels of exposure.

With chimneys, fireplaces and furnaces, most carbon monoxide problems occur because of improper exhausting of fumes. Such problems are almost entirely avoidable through regular inspection by trained eyes.

Another major threat posed by inadequate maintenance is chimney fires. As fires burn, they generate smoke. As the smoke rises up the chimney, it comes into contact with the relatively cooler interior of the chimney (the flue), where some of the smoke condenses, like steam on a glass of cold water. The resulting condensed smoke is called creosote. Creosote is a black or brown gummy substance that builds up on the flue. Once a sufficient amount of creosote builds up, it can catch fire. The resulting chimney fire can range from being barely noticeable to being so dramatic that it sounds like a low flying jet.

The danger in chimney fires comes from the extremely high temperatures generated, which can severely damage the mortar in the chimney and even ignite nearby burnable surfaces. The first fire in a chimney may not even be noticed or, if noticed, may instill a false confidence in the owner (noticing that they had one chimney fire and seeing no harm done, they conclude that the hazard doesn’t apply to their circumstances). In many cases, the first chimney fire can cause cracks and loosen mortar joints that then provide the next fire with an avenue to reach the roof timbers and other combustible materials. Typically, chimney fires that spread to the rest of the house do so very quickly and consume the entire house before being brought under control. The high temperatures cause them to spread extremely fast, often trapping people in upper story bedrooms.

A third major danger from poorly maintained chimneys is failure of the basic structure itself. As discussed above, chimney fires can damage the mortar joints and cause cracks that crumble further with continued “small” chimney fires. Even before the second chimney fire has the opportunity to penetrate the cracks caused by the first, carbon monoxide can escape the chimney and leak into the living quarters of the home. Brain damage and death can occur before anyone has even noticed a problem.

Chimney Inspection/Cleaning Schedule and Costs

As frightening and fierce as the potential fireplace and chimney hazards are, they are almost entirely preventable. The Chimney Safety Institute recommends that homeowners who light fires in their fireplaces three or more times a week during the heating season should have their chimneys inspected and cleaned once a year. If unseasoned wood is burned in the fireplace, twice-a-year cleaning and inspection may be necessary, because unseasoned wood usually burns at a lower temperature than seasoned wood, causing more smoke and therefore more creosote. Some people assume that because they don’t have fires continuously during the winter, they don’t have to worry too much about creosote buildup. This may be far from the truth. The colder the flue, the greater the condensation, so creosote buildup is the greatest at the beginning of a fire, in the time before the flue has fully heated up.

The Chimney Safety Institute recommends that if you use the chimney, wood stove, or free-standing fireplace less than three times a week, you should have the chimney inspected at least once a year and cleaned if necessary. Inspections typically cost from $30 to $50 and cleaning typically costs from $60 to $130. Neither is a major expense in light of the safety issues and the cost of major chimney repairs that can result from poor maintenance.

What A Chimney Sweep/Inspector Will Check

As part of a thorough inspection, an experienced, trained chimney sweep will check the chimney flue, the fireplace, the damper (which opens to allow smoke to escape and closes to prevent drafts when there is no fire), the outside chimney, the chimney top, and the exhaust flues from the hot water heater and the furnace. The inspection will usually identify problems or potential problems that cause chimney fires, premature structural failure, and carbon monoxide poisoning.

A damper that doesn’t close completely when the fireplace is not in use can be a big energy waster. On the other hand, if the damper doesn’t open all the way you risk having smoke and fumes back up into your home.

Some fireplaces have a trap door or removable brick where ashes can be swept down a chute. This eliminates the need to constantly clean the ashes out of your fireplace by carrying them through the house. However, the ash dump itself, which usually has a door at the base of the chimney in the basement, needs to be cleaned out periodically.

Some chimneys also have an air intake duct from the outside of the home to the hearth to provide oxygen to the fire without creating drafts through the house. The grills on either end of the duct should be removed and the duct cleaned out.

When checking the outside of the chimney, the chimney sweep will pay close attention to the chimney flashing. Flashing is the sheets of metal installed where the roof meets the chimney, and helps prevent water from penetrating the roof or the chimney. Timely repairs to your flashing can prevent roof leaks and the myriad of problems associated with them. Flashing also plays an important role in preventing water from penetrating the chimney itself. Water can be extremely damaging to chimneys. It primarily causes problems when it freezes. Water expands as it freezes, causing mortar and bricks to crack or dislodge. Even without freezing, water eats away at components in the mortar, weakening it over time. For the same reason, the inspection should include all the masonry joints on the exterior of the chimney. If cracked and crumbling mortar is discovered, the mortar joints will have to be scraped out and repointed (pressing new mortar into the joints and smoothing the surface). Many experts recommend treating the entire chimney with a sealant to help it defend itself against water penetration. While the sealant can be very effective, it will not help a wall that is in need of repairs. In that case, the repairs should be done first, or the sealant may end up keeping water in rather than out.

The top of the chimney is especially vulnerable to water. The crown (sometimes called the cap) is a mound of cement that surrounds the flue openings and sheds water toward the edges of the chimney. After 15 to 20 years, the crown usually needs to be repaired or replaced. Failure to maintain or replace the crown will allow water to get down into the bricks and mortar of the chimney and can cause severe problems over time – often necessitating the costly rebuilding of the entire chimney.

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