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Chimney maintenance is critical to maintaining a safe home; however, most homeowners rarely, if ever, have their chimney (and the appliance(s) venting into it) professionally cleaned and serviced on a regular basis. Any chimney, whether used with a fireplace or a wood or pellet stove or simply for venting a heating system or water heater, can be damaged due to water entry or interior blockage. While this can include water damage into the structure, an even greater concern is that a blocked chimney can potentially increase the chance of a house fire and/or dangerous exhaust gases (such as carbon monoxide) filling the home.

The National Fire Protection Association (NFPA) and Chimney Safety Institute of America (CSIA) recommend a level two inspection of all chimneys for all real estate transactions. Home buyers would greatly benefit from knowing whether the chimney and the system(s) venting into the chimney are safe to use and are in functional condition. Since chimney repairs can potentially be very expensive, knowing the condition of the chimney when the sales contract is still being negotiated can potentially save the home buyer a considerable amount of money.

A level two chimney inspection consists of cleaning the chimney’s interior, detailed inspection of the chimney’s exterior and video or still photography of the chimney’s interior. Such an inspection is well outside the scope of a home inspection. Very little, if any, of the chimney’s interior is visible to a home inspector which is why this third party service is so important.

What is done as part of a home inspection?

In the course of a home inspection, the inspector will view the chimney from the exterior and inspect the visible portions of the firebox from the interior. If a wood burning insert is installed, the home inspection is limited to the chimney’s exterior. Removing/disassembling a wood-burning insert or pellet stove is well outside the scope of a home inspection, and some of these older systems were not properly installed. The inspector is not performing a code inspection nor verifying that the unit was installed per manufacturer’s instructions. When an insert exists, the best bet is to consult a certified chimney professional. The chimney professional will remove the insert and ensure that the flue is properly attached and in satisfactory condition.

The inspector will look for visual damage to the chimney’s exterior such as cracks in the crown or missing mortar in the chimney’s sides. We also look at the chimney’s height. Generally there is a 3-10-2 rule for chimneys — chimneys must penetrate the roof at least three feet and must also be two feet taller than anything within 10 feet of the chimney. A chimney that terminates too short may not draft properly due to air currents affected by nearby roofing, for example. Tree branches should also be kept trimmed away from chimneys.

Damage or cracks to the masonry can allow water in, and that can lead to much worse damage down the road. Loose bricks can also fall and damage the roof below or injure someone on the ground.


This chimney has considerable mortar deterioration allowing me to literally remove bricks. This condition can allow considerable water to infiltrate the chimney as well as allow bricks to possibly hit someone on the ground.

   
This chimney has a damaged crown (aka mortar wash or crown) as well as cracks in the chimney masonry.

While inspecting the chimney’s exterior, the flashing is also checked to prevent roof leaks. Often a roof leak will occur where there is a penetration through the roof, such as at chimneys, vent stacks or skylights. Preventive maintenance is key to helping prevent leakage. Chimney and other roof flashings should be regularly checked and resealed as needed.

The condition of the interior flue liner is rarely, if ever, visible to the home inspector. Chimneys built before 1940 were normally not lined; however, a proper liner is often needed to safely vent a gas- or oil-fired appliance into the chimney. After many decades of a gas- or oil-fired appliances venting into an unlined chimney, there will likely be interior (hidden) deterioration by this point. Relining a chimney with stainless steel is possible yet quite expensive.

I also always recommend that a proper rain cap be installed at the top of the chimney to prevent debris, animals, rain water, etc. from entering the chimney. Each flue within the chimney should have a rain cap installed.

The inspector will check for deteriorated masonry within the firebox, plus check for cracks and ensure that the damper functions properly.

What about gas fireplaces?

There are two types of gas fireplaces — gas inserts and gas logs installed into a prior wood-burning fireplace. A natural gas or propane insert are the most common in modern homes, and they are generally vented directly to the home’s exterior — normally directly behind the fireplace. The assembly is metal with a glass front, and a gas line enters the fireplace normally from the side. Some units have blowers installed as well.

For a gas fireplace conversion from wood to gas/propane, a gas log set would be installed with a gas line run into the firebox. The damper should have a small clamp installed to keep the flue damper slightly open if the unit will have a running pilot light. Doing this helps prevent the possible risk of carbon monoxide accumulation in the home from the fireplace.

As far as the inspection of these units, the inspector does a basic on/off test to make sure the unit turns on. The units are not disassembled; and once installed, the gas insert’s flue is not visible. Of course the pilot, if applicable, must be on for the inspector to test the fireplace as we do not light pilot lights for liability reasons. These units can be operated manually with a dial or with a remote control installed to allow turning the unit on and off from across the room.

Hearth Extension — Often Overlooked

The inspector should ensure that besides the firebox itself that the hearth extension (the area in front of the firebox) is properly sized. Many homes have insufficiently sized hearth extensions which can increase the chance of a house fire. When the firebox opening is less than six square feet in size, the hearth extension should extend at least 16 inches in front of and at least eight inches beyond each side of the firebox opening. When the firebox opening is six square feet or larger, the hearth extension should extend at least 20 inches in front of and at least 12 inches beyond each side of the fireplace opening.

The hearth extension has several functions including helping to keep heat from the firebox away from combustible flooring such as carpet or wood. A log rolling out of the firebox or hot embers hitting carpeting or wood flooring could obviously start a house fire. A hearth extension should be a non-combustible material like tile, brick, concrete or stone.


This hearth extension of this fireplace is only 14 inches deep and presents a potential house fire hazard. Multiple burn makes existed on the adjacent carpeting.

Only seasoned dry wood should be used in wood-burning fireplaces and stoves. Doing so helps limit the accumulation of creosote within the firebox, smoke chamber and flue. Creosote is a black tar-like substance from condensed flue gases and unburnt carbon that exists in firewood. A fire burning hot helps keep the flue gases and particles hot as they exit the chimney, whereas a lower temperature fire allows this material to condense as it rises up the chimney and to get stuck there. The photo below shows creosote accumulation in a flue and throat (the area above the firebox). The fireplace/chimney should be properly cleaned and inspected before further use.

Homes with fireplaces, wood or pellet stoves, or any fossil fuel appliance (gas, oil, LP) or even an attached garage should have at least one carbon monoxide (CO) detector installed. Most CO detectors should be replaced every five to seven years although some newer ones have a 10-year design life. Simply pressing the TEST button on a smoke or CO detector only tells you whether the unit is powered — it does not tell you that the sensor will function in an emergency. This is why regularly replacing smoke and CO detectors is critical for home safety.

Having chimneys, fireplaces, stoves, etc. inspected annually by a qualified fireplace/chimney professional helps ensure comfort and safety throughout the year.

Matthew Steger, ACI, WIN Home Inspection 

Facts, opinions and information expressed in the Closing Comments Blog represent the work of the author and are believed to be accurate, but are not guaranteed. The Lancaster County Association of Realtors® is not liable for any potential errors, omissions or outdated information. If errors are noted within a post, please notify the Association. Posts represent the author’s opinion and are not necessarily the opinion of the Association.

Lancaster County Association of Realtors®

Lancaster County Association of Realtors®