Water damage to chimneys & flues:

This article describes water leaks and moisture that damage masonry and metal chimneys and the heating appliances that are connected to them.

We list the common sources of water and leaks and we include warnings for inspectors who need to examine equipment as well as the chimney itself when water or moisture leaks are detected.

Moisture Problems that Damage Chimneys

Our photograph at the top of this page shows a stunning waterfall flowing out of a "sealed" chimney cleanout in a basement. Lots of roof spillage or surface runoff was entering the base of this chimney and also pouring out of the chimney cleanout during a heavy rainstorm.

Readers of this article should also see CHIMNEY COLLAPSE RISKS, REPAIRS.

Moisture is the major cause of chimney corrosion and disintegration in both masonry and metal chimneys. The flue gases are acidic in nature and if allowed to condense and saturate the masonry or joints in metal flues the destructive results will soon be apparent.

Mechanical problems in the construction or settlement after construction and over firing or flue fires will also contribute to the problems.

External moisture enters the chimney through cracked caps, porous masonry, poor mortar joints and improperly designed and installed roof flashings. Internal moisture (condensation) collects in cracked or separated flue tiles, blocked flues and chimney caps.

Masonry chimneys subjected to moisture damage can have efflorescent salt stains, spalled bricks, eroded mortar joints, flaked cracks in the ceramic flue liner and cracked caps.

Metal components of a vent system can have rust and white acid stains at joints, corrosion holes along the bottom of horizontal connectors and corroded chimney cleanout doors at the base of the flue.

Moisture enters a chimney structure from several locations:

• Missing chimney cap lets wind blown rain and snow enter the flue
• Damaged chimney crown lets water enter the chimney structure
• Leaks at the chimney sides let wind-blown rain enter the chimney structure
• Leaks at chimney flashing let water enter the chimney structure
• Ground and surface runoff or roof spillage by a building often enter the base of a chimney that extends below ground.

Water leaks into a Chimney can Damage the Chimney and the Appliances Connected to It

The result of leaks into a chimney can be unsafe heating equipment as well as costly damage to the chimney, the appliances connected to it, and to the building itself.

• Frost or water damage can crack or break a masonry clay chimney tile resulting in fire or flue gas hazards at the building
• Broken chimney flue liner parts can obstruct the chimney flue resulting in dangerous, potentially fatal carbon monoxide gas hazards
• Water entering the heating appliance such as a furnace, boiler, water heater or woodstove can cause rust damage to the heater components or can damage electrical controls on the appliance, leading to costly repairs
• Water entering a wood-framed chimney chase can also invite insects, rot, or mold problems in the building
• Water entering a metal chimney or flue can cause corrosion or rust which perforate the chimney or flue vent connector leading to equipment failure, improper operation, and dangerous flue gas leaks in the building.
  
  Even a stainless steel manufactured chimney is not immune to rust and corrosion when it faces the combination of water in the flue interior (or between the layers of metal of a multi-wall chimney) and corrosive acids that form as soot and creosote are dissolved by the water in the flue.

Watch out: water leaks or high levels of condensation in a chimney are dangerous, risking damage to heating equipment, other metal chimney flue or vent connectors, and in-turn, improper and unsafe heating equipment operation that can include both the building damage ensuing if there is loss of heat during freezing weather, and most serious, a building fire or fatal carbon monoxide poisoning of building occupants.

Where do Most Leaks Occur at Chimneys?

We can't find the leak in our chimney

Our reader asked:

Our chimney leaks every time it rains heavy.

We have had a builder and roofer out over the last two years who have made various changes (or they told us they have), however its still dripping and letting rain water in. Any ideas?

This question and our reply were posted originally

at CHIMNEY CRACK DETECTION & DIAGNOSIS

Sketch above / left showing improper slope on the masonry cap of a chimney and also the omission of a rain cap atop the chimney flue and our chimney drawing below were provided by Carson Dunlop Associates, a Toronto home inspection, report writing & education firm. 2017/09/10 Laura

Reply: where to look for leaks on or around chimneys

Laura,

It sounds as if the people working on the problem have tried solutions without finding the actual leak source.

I'd start by trying to find, more accurately, just where water is coming in to the building:

• is it a roof flashing problem (leaks where a chimney passes through the roof) ,
• a chimney rain-cap or top seal problem (water enters at or near the top of the chimney),
• a chimney body problem (water enters somewhere along the route of the chimney parts that are exposed outside), or a
• groundwater problem - water enters at the chimney base or from ground level or below, or less common,
• an internal leak into a chimney (from a nearby leaky supply or drain pipe).

You might get a more clear understanding of the leak by asking for an inspection by a chimney sweep who's certified (National Chimney Sweeps Guild) and who can examine both the entire exterior and the entire flue interior of the chimney to see where water is originating.

I suggest preparing yourself by reading over some of the chimney leak diagnosis and repair articles I'll give below, to become familiar with the different types of leaks that occur in or on or around chimneys.

Note that some of these leak problems occur only on brick or other masonry chimneys while others like CHIMNEY CHASE CONSTRUCTION will discuss leak points that only occur around the top of a wood-framed and enclosed metal chimney.

 

A repair person deliberately routed rainwater into our chimney flue: is this normal?

An InspectApedia reader asked:

I live in an apartment block which has 2 flats and I live on the ground floor.

I have lived in my apartment for 8 years with no problems with the chimney, recently a new couple moved in upstairs and he has had some work done on the chimney.

He told me that he had water coming in his roof (it is a shared chimney breast but has 2 separate flues), so he employed someone to come and fit a different chimney hood and also a pipe to divert any rainwater etc into the inspection flue.

This has now caused an issue for me which is that now I have water running out of the inspection hatch and down my wall, he has said that it is normal to divert the water in the way he had it done, and the reason the water is running down the wall is because the bottom of the inspection hole is level and should be below the level of the hatch, the inspection port is angled

I have attached a couple of pictures, but could you tell me if this is normal? - 2018/10/02 Anonymous

Reply: deliberately sending water into a chimney flue is not normal and not safe

Opinion:

Forgive me but I don't know what is meant by an "inspection flue" - chimneys don't to my knowledge have an "inspection flue" and since each flue in a chimney has to be physically separate from all of the others, from point of use to rooftop, such a flue would not permit inspection of the in-use flues anyway.

I think that you meant the chimney cleanout door - which is what I see in your photo.

The cleanout door / opening is there to permit chimney cleaning and inspection of a chimney flue that is in turn used by a heating appliance.

All of the comments about blaming water leaks on the cleanout door in any way are incorrect.

Water coming out of the cleanout or coming into and out of a chimney anywhere is improper and dangerous; in other words, nothing is normal nor proper about having water running into or out of a chimney. Chimneys are meant to safely conduct combustion gas products out of the building and above the roof line.

Chimney flues are not meant to receive nor conduct rainwater or any other water.

Diverting rainwater INTO a chimney anywhere makes not an iota of sense; unless we've misunderstood what was done, that would be a very serious error.

The potential hazards from sending water deliberately into a chimney are very serious, risking costly damage or destruction of heating equipment, building leaks, mold, rot, or insect damage, water damage, and most-seriously, flue damage that risks a building fire or fatal carbon monoxide poisoning.

Watch out: Because there are serious hazards and because if what you described is accurate, there is a high probability that work was done by someone incompetent and dangerous, all parties affected by or using any part of the chimney you describe should have the chimney inspected for safety and for proper function, using the services of a qualified chimney expert such as a chimney sweep who is certified.

In the U.S. chimney sweeps meeting at least minimum qualifications are certified (at more than one level of expertise) by the National Chimney Sweeps guild (http://www.csia.org/) . In Europe there are different associations such as
the
International Union of European Chimney Sweep Workers (ICU) Representing worker sweeps and apprentices (trade union) http://www.icu.li/
OR
the European Federation of Chimney Sweeps (ESCHFOE) http://www.eschfoe.com/

Our complete list of contacts for chimney cleaning professionals by country is found

at CHIMNEY SWEEP ASSOCIATIONS

...

Continue reading at CHIMNEY INSPECTION at ROOFTOP or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Chimney Leak Articles

• CHIMNEY CAP & CROWN DEFINITIONS - difference between a chimney rain cap and a chimney top seal - two different possible leak problems.
• CHIMNEY CRACK DETECTION & DIAGNOSIS - leaks may occur in a masonry chimney that is damaged by frost, settlement, movement - such chimneys are probably unsafe
• CHIMNEY DAMAGE by LEAKS & FROST - How water and moisture leak into and damage chimneys and heating appliances.
• CHIMNEY INSPECTION from GROUND
• CHIMNEY INSPECTION at ROOFTOP
• CHIMNEY RAIN CAP / RAIN COVER INSPECTION
• CHIMNEY REPAIRS, TOP & CLAY FLUE TILE for leaks at the top seal or top of the chimney
• CHIMNEY SHOULDER LEAKS - if it's a brick chimney there may be leaks along the point where the chimney widens out as it nears its base
• CHIMNEY STAINS & LEAKS - stains can help track down where water is getting into a chimney - where I have posted your question and my reply
• CHIMNEY WET TIME & CORROSION - effects of moisture on metal chimneys & flues
• DRIPPING WATER SOUND SOURCES
• FLASHING, CHIMNEY MISTAKES & LEAKS - leaks where a chimney passes through a roof or eaves or soffit

Suggested citation for this web page

CHIMNEY DAMAGE by LEAKS & FROST at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to CHIMNEYS & FLUES

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Questions & answers or comments about how to spot water or frost damage to chimneys & how that chimney damage may be repaired.