Chimney condesation

David_19

We installed a new roof for a customer last summer, which included reflashing the chimney. No leaks, nice job. Until heating season. Water coming from behind chimney flashing and running down the underside of the sheathing. My theory (coming from a Remodeler) is that moisture coming up the chimney (brick, unlined) is going through the brick and condensating on the back of the flashing. Am I on the right track? Will a liner take care of this problem or is there other simple solutions?

Thanks,

David

Ken_8

Extremely unlikely

Unless the chimney is an absolute seive, what you suggest is not possible.

At this relatively warm time of year, little if any combustion gasses will condense in the chimney anyhow. What "forces" are you suggesting would make the water/condensate permeate bricks? If condensation were occuring in the manner you suggest, the evidence would also exist in the chimney base where all or most of the condensate would puddle.

Then too, a water heater was probably "on" all year long. That would have been a condensate producer as well.

Did the homeowner put a new boiler in since you did the roof? If not, the only thing that changed was your new roof.

The chimney may be cracked on the exterior and simply leaking rain water into the rafters.

Keep in mind many of us believe an all-masonry chimney is best; as long as a fire clay liner is in place and has no obvious deterioration.

I urge you to carefully re-examine the flashing and tar job. While up there, check all four sides of the chimney's exterior for cracks that would result in this leak.

If the chimney needs a liner, one should be installed. But bear in mind, if he lines the chimney and still has a roof leak, you're in deep do-do.

Let us know how you make out.



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David_19

Ok, I forgot to mention a critical point. No Rain or snow outside...just cold. Chimney is apox.100 years old but in decent shape. Leak is only on one side. Chimney serves water heater furnace which is over 10 years old.

David

Constantin

Could be the furnace/water heater...

...our rear chimney was orphaned with but a water heater attached to it. Like yours, it consisted of a single row of bricks, no lining, etc. As a result, the brick turned to red dust in the basement and even on the second floor, the moisture meter our house inspector carried showed 94+% water content (!!!)

It is entirely possible for the chimney to be wet on the inside as it gets colder, as I am willing to be an ice-cream that the flue is oversized. Lining an old chimney should be a matter of course, particularly as more and more efficient heating appliances are attached to the chimney...

Furthermore, I could imagine that many homes will have a much lower draft in the chimney as they become tighter and tighter down below. Were any such renovations done this year? (think weatherization, insulation, new doors, windows, etc.)

Bob Harper

wet chimneys

You can be getting moisture from several sources:roofing/flashing, condensation of high indoor Rh on cold surface, rain down the chimney if uncapped, or flue gas condensation.
Roofing/flashing. Just because it was recently redone doesn't guarantee they did it right. I've never had a roofer agree it could be his new roofing job thought I've proven many wrong. Take a hose to the roof and drench the flashing and cricket. If it leaks, call the roofer back. If not, move up the chimney--don't spray it-just drench it. If it manifests inside, call a chimney sweep to address the cap, crown, and pointing. Consider having him treat it with Chimney Saver water repellent Tx.
Indoor condensation. What is your indoor Rh%? Do you have a damp basement? Dryer not vented properly? Stove not vented properly? When interior moisture migrates through walls into interstitial spaces, it cools off to the dewpoint and condenses. The Canadians in British Columbia were telling me horror stories of mold in closets on exterior walls. Maintain a reasonable indoor Rh.
Flue gas condensation. I don't know where Ken is getting his info from but I beg to differ. I've seen water heaters vented into oversized unlined masonry chimneys soggy as hell in summer. How can you make those blanket statements about a chimney you've never seen? It sounds like an exterior unlined oversized heat sink. This sounds like a recipe for condensation to me. Regardless of the condition of the flue, you'll probably need a liner if nothing else for sizing purposes. Now, unless this 100 y/o chimney can pass an NFPA 211 Level II inspection as is, it Must be relined according to NFPA 211, 54, and 31 as well as most model building codes. When you install new equipment of a rating, fuel, or efficieny different from the original, you must get a Level II inspection first. Will a liner guarantee to solve David's water problems? No, but it's a step in the right direction. The chimney may be telling you it has problems. Are we listening?

Anxious to hear some opposing views,
Bob.

David_19

I went back to the job today to double check the flashing, ext. I had posted my question after getting the call and before checking the job trying to get a handle on posible problems. Last fall we had the same problem and I reworked the flashing in case I had messed the original up. The home owner said that everything looked fine when they put the christmas decorations away. But this year when the went to get the stuff out again they found moisture on the roof sheathing and mold over significant portions. I was shocked as it did not look like this last fall. Upon further inspection the chimney showed much sign of moisture coming through, from the attic floor up to the roof. Outside temp. was around 40. The sheathing had condensation and mold (pretty grey stuf) all over it.

When I went to the basement to look at the 1968 era furnace the flue pipe showed much damage from condensation (rust, mineral deposits, staining, etc.). I was amazed their CO detector has yet to go off. The owner and I were convinced the problem was the chimney. I am also betting that it was doing it over the summer with the water heater alone. I am having our HVAC trade contractor go out to check it out this week.

Now the question is what changed to start the condensation problem when the new roof went on, since I am fairly confident that the problem was there before.

-Ventilation did not change same number of roof vents as before.

-old roof was cedar shingles with asphalt or metal over it. New roof is OSB over skip sheathing, ice&water shield, felt and ashpalt shingles.

-No soffit venting. Owner did not want the additional expense of reworking soffit venting. "It work fine before..." and I unfotunately agreed.

Could enough air have been coming in the 1/4" gap between the cedar shigles at the eave to vent the moisture out the 4 roof vents? Do HVAC guys deal with attic ventilation?:)

Thanks again for your help.

David

jim lockard

sounds like

A. The chimney will be getting a properly size liner.
B. The H.O. will need to have the attic properly vented.
C. Do not let the CO detector Amaze you the lack of public interest in CO amazing.

Best Wishes J.Lockard

Constantin

Sounds to me like...

.. an abandoned/orphaned chimney syndrome. All summer, that water heater is dumping lots and lost of water into the brick as the colder nights/mornings make it amendable to making the water heater gases condense. Unfortunately, water heaters fire most frequently in the morning, when the chimney is still cold from the night.

Granted, the older, well ventilated attic might have done a better job if drying the exterior of the chimney, but I'm almost willing to bet that the source is the water heater down below. I'd address the source of the problem, an unlined chimney, before trying anything else. It ought to be much less expensive than adding soffits or other features to the home.

At the end of the day, drying out the chimney on the inside of the home isn't going to address the issue, which is how it is being water-logged... only a matter of time before the brick will crumble under such circumstances...

jim lockard

willing to bet

that the chimney section in the attic is damaged.

Robert O'Connor_7

Bob

What is a level II inspection?...Robert O'Connor/NJ