Chimney maintenance is critical, whether the chimney is used with a fireplace or wood stove or simply exhausts the home’s fossil fuel heating system or water heater. While often overlooked by home owners and new buyers alike, a thorough inspection by a certified chimney professional (such as one certified by the Chimney Safety Institute of America) is strongly recommended. For real estate transactions, I recommend a thorough level 2 inspection of all chimneys. Since very little (if any) of the chimney's interior is visually accessible to a home inspector, even if viewed from the firebox, the level 2 inspection can assure the home owner of the overall condition of the chimney and report any potential safety issues. Issues inside the chimney can be very expensive to repair, so finding out the chimney’s true condition is wise. The National Fire Protection Association (NFPA) recommends a level 2 inspection when a home is purchased, when changing the fireplace’s fuel type, when relining the flue, if a building or chimney fire happens, or an operational malfunction or earthquake occurs. The CSIA (Chimney Safety Institute of America) has these same recommendations.
A level 2 inspection entails the certified chimney professional first cleaning the chimney's interior and then performing a thorough inspection of the exterior and interior chimney components as well as the firebox. The level 2 inspection should include the use of video or still photography along the chimney’s full interior length. The chimney professional is looking for evidence of deteriorated masonry and a damage flue liner as well as other issues that may be detrimental to safe use of the system. If damaged masonry or other components are found, they should be repaired. If gaps in the interior masonry are found, for example, this can provide spots where excessive heat or the byproducts of combustion can also enter potentially leading to a house fire or carbon monoxide (CO) entry into living space. The level 2 inspection should also include inspection of crawl spaces, basements, or attic spaces adjacent to the fireplace or chimney to ensure proper clearance from combustibles.
Video describing the differences between Level 1, Level 2, and Level 3 professional chimney inspections. (courtesy of CSIA) A level 2 inspection is recommended for all real estate transfers.
What is done as part of a home inspection?
In the course of a home inspection, the inspector will view the chimney's exterior and the firebox. Very little of the interior of the smoke chamber, throat, and chimney's interior are visible to a home inspector. This is why having this system thoroughly evaluated prior to closing is so important. If a wood burning insert or stove is installed, the area behind the insert is not visible to a home inspector.
Removing a wood burning insert or pellet stove is well outside the scope of a home inspection, yet many of these older systems are not properly installed. The home inspector is not performing a code inspection, nor verifying that the unit was installed per manufacturer’s instructions. When an insert exists, a certified fireplace/chimney professional should be consulted. The chimney professional can remove the insert and ensure that the flue is properly attached, inspect and clean the entire system, as well as research to confirm the manufacturer's installation specifications. Home inspectors are not trained or certified to perform level 2 or other invasive chimney inspections, so only relying on the home inspector’s non-invasive inspection doesn’t tell you the whole story. Remember that home inspectors are generalists, not specialists and that the home inspection is a non-invasive visual inspection. A certified chimney professional is the specialist and can do a more invasive analysis of the whole system.
On the chimney’s exterior, the home inspector will look for visual damage to the chimney (such as cracks in the brick/stone, flue, or mortar cap [aka, a chimney crown]), indications that a flue liner is present (terra cotta or metal), and even look at the chimney’s height. Generally, there is a 3-10-2 rule for chimneys. This rule says that chimneys must penetrate the roof by at least 3 feet and must also be 2 feet taller than anything within a 10 foot radius of the chimney. I occasionally run across chimneys that appear to be too short and the adjacent roof peak is at nearly the same height or sometimes higher than the chimney just a few feet away. This can lead to improper venting of the chimney and may present a house fire hazard. I’ve also seen other roof vents immediately adjacent to the chimney that are simply too close.
When damaged masonry or a deteriorated mortar cap is found, repair is recommended. Cracks in brick and mortar or the mortar cap can allow for water infiltration and lead to further damage from freeze/thaw cycles. Loose bricks can also fall and damage the roof below or injure someone on the ground.
Fully deteriorated mortar cap with the top 3 coursed of bricks readily disassembled. Water enters here and causes additional freeze/thaw damage and potentially damages the home. This chimney needs to be completely rebuilt.
This chimney has a damaged mortar cap (aka 'mortar wash' or 'crown') as well as cracks in the chimney masonry. This issue is not uncommon with most chimneys.
This chimney is totally missing its crown. This allow water to readily enter the masonry along the flue liner and cause damage in the chimney and, likely, inside the home. A professional masonry should be consulted to install a proper concrete crown and extend the flue liner.
This chimney is also missing a crown and the large unsealed opening can allow rodents/animals, water, debris, etc. entry.
This is what a proper chimney crown should look like. Notice how it overhangs the chimney masonry to shed water away from the bricks.
While inspecting the chimney’s exterior, the roof flashing is also checked. 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. Tree branches should be trimmed at least 10 feet away from the chimney to help prevent them from possibly affecting proper draft.
The inspector will also look for leaning of the chimney. Of course, if this is allowed to continue, it may collapse at some point. Bracing or other repair may help prevent a collapse. Attaching overhead utility lines and TV antennas to a chimney is not a good idea since these can put extra stress on the chimney and may lead to future problems.
As mentioned above, since the home inspector can not see the majority of the chimney's interior. Terra cotta liners may be cracked or misaligned due to settlement and age or it may be altogether missing (common in pre-1940s homes). This liner damage can allow interior deterioration due to rain water and exhaust gases reacting with each other. Also, unlined chimneys allow heat to pass through chimney walls very quickly which can lead to a house fire. Animals such as birds, raccoons, or squirrels like to nest in chimneys for protection and warmth; nests can block the flue and prevent proper venting. All of the above can spell problems. Improper or blocked venting may allow dangerous exhaust gases, such as carbon monoxide, into the living space which can be deadly.
I also recommend approved flue or chimney covers (also known as a 'flue cap' or 'rain cap') be installed on the top of each flue. These covers have flat sheet metal on the top and wire mesh/screening on the sides. The cover helps keep rain water, leaves, debris, and animals out of the flue, yet still allows exhaust gases to vent out. Metal flue liners often have their own metal cover which performs the same function. I also notice that some homes have a chimney with multiple flues but a cap is only installed on one flue; what's to keep rain, debris, or animals from getting into the other (uncovered) flue?
The flue damper is commonly a small door above the firebox that closes off the fireplace from the chimney when the fireplace is not in use. If the fireplace’s damper is missing or damaged, a flue top cover on a spring and chain is a repair option. This type of cover is hinged and when a fire is going to be started, the damper is opened from the firebox by pulling on the chain. Afterwards, the flue can be closed again by using the chain within the firebox.
On the home’s interior, the home inspector will view the firebox and hearth extension and possibly a small amount of the bottom of the flue, if visible. He will also check the flue damper and fresh air vent (if equipped). Of course, home inspectors do not light/ignite wood fireplaces or coal/wood/pellet stoves for liability reasons.
There are masonry gaps existing in this fireplace's smoke chamber. Fire, soot, or creosote
could get trapped here and start a wall fire. These gaps are nearly impossible to clean.
When the firebox opening is less than 6 square feet in size, the hearth extension should extend at least 16 inches in front of and at least 8 inches beyond each side of the firebox opening. When the firebox opening is 6 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. If there is a concrete, tile, or brick floor covering in front of the fireplace's hearth extension, a short hearth extension is likely not an issue since these type of floor coverings are not combustible. Here in Pennsylvania, most areas had no building codes until 2004 so it is not uncommon to find fireplaces in homes with very small hearths. The hearth extension has several functions, such as helping to keep the fireplace's intense heat away from combustible materials (such as carpet or wood flooring) as well as providing a non-combustible surface should hot embers or a burning log roll out of the firebox. A shallow hearth extension presents a possible fire hazard. The hearth extension should be constructed of a non-combustible surface (and is often brick) and be at least 2" thick. In a few homes, I’ve found no hearth extension whatsoever and wood flooring or carpet were terminating right up to the firebox. A potential recipe for disaster. One loose log rolling out or a spark escaping from the fireplace could easily start a house fire.
This wood burning fireplace has no hearth extension
and adjacent wood (combustible) flooring.
When burning wood, it is wise to burn only seasoned dry wood. Trying to burn green or damp wood will lead to a smoky fire (assuming you can get it lit) and a better chance of creosote accumulation in the firebox and flue. Creosote is a black tar-like substance from condensed flue gases and unburnt carbon. When a hot fire is burnt, this helps keep the flue gases and particles hot as they rise and exit the chimney's top. A lower temperature fire allows this material to condense as it rises up the chimney and possibly get stuck on the chimney's interior. Next time the fireplace is used, this creosote may re-ignite inside the chimney.
The creosote coating the interior of this fireplace's flue and smoke chamber may lead to a chimney fire.
Home inspectors do not light fireplaces or pilot lights. When the home has a gas (natural gas or LP) fireplace, the system should be ready to go for the inspection. This means the seller should have the pilot lit. The inspector will use the normal operating control (normally, either a wall or unit mounted switch or a remote control) to start up the unit. The inspector will run the gas fireplace for a short period of time and also open the access panel under the unit, if equipped. Within this location, the inspector can verify whether a gas shutoff valve is present and also visually inspect the condition of the exposed fuel line. Gas fireplaces are generally considered decorative appliances; modern building standards don't require a gas valve immediately adjacent to decorative appliances, but there should, at least, be a shutoff valve somewhere just upstream in the gas line. The gas valve should allow the gas only to this appliance to be controlled. For other gas appliances (such as a furnace, boiler, clothes dryer or stove/oven), there should be a gas valve within 6' and within the same room of these appliances. This rule generally does not pertain to gas fireplaces.
In many cases, a wood burning fireplace can be converted to a gas log unit. Instead of burning wood, it would burn natural gas or LP (propane). A gas line would need to be run into the fireplace and, of course, a gas logset would need to be installed. This gas fireplace would still need to use the chimney. A metal liner will likely be required to ensure the gas fireplace's exhaust gases make their way up the chimney and out of the home. In all cases, the chimney's exterior should still be maintained as any damage to it can still damage the home such as allowing water infiltration occur.
One has to be careful when running corrugated stainless steel tubing (often called CSST and normally coated in yellow or black) into a gas fireplace. CSST is a yellow or black insulated semi-flexible gas line. Often, these fireplaces have round or square openings in the metal chassis; these openings tend to be sharp and may have burrs. Since CSST has relatively thin (only 0.010" thick) walls, it doesn’t take very much pressure to damage to puncture CSST. Most plumbing and natural gas requirements call for protection from mechanical damage. Therefore, running CSST into the fireplace with a short PVC sleeve, a rubber grommet, or simply not using CSST at this location at all is an option. Black steel pipe or rigid copper tubing is an alternative.
Installing a carbon monoxide detector near any fireplace or wood/coal stove is wise. Also, if a gas log has been installed into a fireplace with a damper (such as one previously used for burning wood), a proper clamp should be installed on the damper to make sure it can’t be fully closed. Even an active pilot light for a gas logset may allow for carbon monoxide accumulation; the slightly open damper will allow this exhaust to vent outside.
We still occasionally see unvented gas/LP fireplaces. These are units that do not have a flue or chimney. These units rely on complete gas combustion. They will have an oxygen-depletion sensor who's function is to determine if the room has insufficient oxygen for combustion due to high carbon monoxide (CO) levels. Should incomplete combustion occur, the home could fill with CO and the sensor will hopefully turn off the fireplace. I don't know how fail-proof these oxygen-depletion sensor are so I don't recommend unvented gas fireplaces. More and more states are banning these units due to the increase safety risk. Vented gas fireplaces are safer.
If the chimney only vents a fossil fuel heating system or water heater, special attention needs to be given to the location and pitch of the appliance connector exhaust pipe(s) and how they are sealed into the chimney. If there is a large metal connector pipe for an oil fired furnace and a small metal connector vent pipe for a water heater, for example, the smaller pipe should enter the chimney above the location where the larger furnace vent pipe enters. The larger BTU appliance should be the lower of the vent connections into the chimney so it can help draft both appliances.
Chimneys used for any purpose (unless officially sealed and out of service) should be inspected regularly by a certified and qualified chimney professional. If the chimney is only venting a fossil fuel (gas, LP, or fuel oil) heating system or water heater, having the chimney inspected when the HVAC system is cleaned annually is a good choice for safe operation.
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© 2020 Matthew Steger
Matthew Steger, owner/inspector of WIN Home Inspection, is a Certified Level 1 Infrared Thermographer, an ASHI Certified Inspector (ACI), and an electrical engineer. He can be reached at: 717-361-9467 or firstname.lastname@example.org.
WIN Home Inspection has provided a wide array of home inspection services in the Lancaster, PA area since 2002. This article was authored by Matthew Steger, ACI - owner of WIN Home Inspection in Lancaster, PA. No article, or portion thereof, may be reproduced or copied without prior written consent of Matthew Steger.