I have an exterior Chimney that was built about 5 years ago, it serves a fireplace and boiler, during the winter it develops a white chalk powder on the top 1/3 of the chimney, should I be concerned, should I have this checked out?
thanks,
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That is efflorescence. Mineral salts that leaches out with water.
The powder is not a problem except for the appearance, but the fact that you have this much moisture passing thru the masonry is a bad thing. Need to water proof the cap
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thank you all for the advice, I will make sure the metal cap is in place over each flue and that the cement cap is intact. thanks again.
>>and that the cement cap is intactAnd, ideally, overhangs the brick on all 4 sides by 2"+/-.Rarely done right in my area - maybe 1 in 100 based on my inspections.
"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."
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actually, I didn't mean flue caps. I meant a chimney cap.a mud dome cap is pretty thin sometimes and no cement is water proof. The thinner a mud cap is and the less well domed it is to drain water away, the more likely it is that water is seeping right through it. There are a lot of ways to deal with it, but I would need a photo to begin to say the best one for you. One good one is a stone mantle cap over the whole thing, about 12" above the flues.
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I believe that an oversized chimney which never gets properly heated up and thus condenses the flue gas can cause a similar effect. The higher the efficiency a boiler or furnace is, the cooler the flue gas and thus the easier it is to start condensing out moisture.
True, but that condensate runs back down the flue, rarely percing out through the brick.This is from the rain and snow when specifically at the top of the chimney.
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I don't see that Pif .. need more info, is this a clay liner .. is the boiler a steel/abs flue inside the brick chimney .. is it leaking ... does the fpl damper close completely, or is it constantly lettng warm air in ..
It is only 8 years old. That and the symptoms tell me all I need to know to diagnose this with 99% certainty.
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Hi Piffin,Allow me to disagree a bit. Anecdotal evidence in my home points to oversized masonary chimneys being quite good at retaining water. The rear (now dearly departed) chimney only had a Gas water heater on it, moisture meter on the exterior of the brick on the 2nd floor was in excess of 97% (no liner, single layer of brick). In the basement, winter spalling had opened fist sized-holes and reduced the brick strength to brown powder.So, while a chimney cap may help, I would first make sure that the two appliances are venting into an appropriately sized flue. The more the flue is oversized, the bigger the potential condensation issues. IIRC, low-mass flue materials like B-vent that is surrounded by vermiculite is also preferable to lined masonary chimneys - no leaching, less mass = less opportunity for flue products to get into the chimney materials or the house.While we could have perhaps saved the front chimney, we took that one down also, replaced it with a lined (SS) masonary chimney with individual flue pipes (one for the boiler, one for each fireplace). The space between the SS pipes is insulated with vermiculite. Hopefully, that tactic will keep the condensation of creosote, oil flue products (especially suphuric acid) to a minimum. Lymance tops for the fireplaces and a chimney cap for rodent / bird control round it all out.Time will tell if we did the right thing. What I can tell you is that the powder coat on the underside of the chimney cap has been eaten off by the boiler flue gases and bare metal is now visible there. The other part of the chimney cap is happy as ever. Some day, I may replace that cap with a copper one, then the sulphuric acid will produce a nice green patina!
"I would first make sure that the two appliances are venting into an appropriately sized flue. The more the flue is oversized, the bigger the potential condensation issues."I know all that, but maybe you are right....thing is, I assume from the fact that it is only 8 YO that it was designed and built to modern standards, so it would be sized right.I know, I know.. assumptions killed the cat one of his nine lives, right after curiosity...;)
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>>Anecdotal evidence in my home points to oversized masonary chimneys being quite good at retaining water. The rear (now dearly departed) chimney only had a Gas water heater on it, moisture meter on the exterior of the brick on the 2nd floor was in excess of 97% (no liner,Older house? (Darned well should be with no liner) Used to vet a furnace too? Replaced it with a high efficiency?In my area, if it's an exterior chimney - it was required to be lined for the WH when they changed the furnace - and the good HVAC techs would have regardless of location because of (i) reduced BTU input and - particularly - no liner.For an 8 year old house, the problem is unlikely over-sizing. Possible, but unlikelyI agree with Piffin's take.
"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."
Howard Thurman
Older house, yup! 130-YO at that point. Chimneys built for coal fireplaces and stoves, not small gas or oil appliances. Single-layer brick with plenty of holes. The good draft established by the many holes in the basement probably saved the inhabitants from potential CO poisonings. Another potential issue is not putting in a new (smaller ID) liner when a right-sized appliance is substituted for a over-sized previous one. Not likely in this case, but it happens also.
>>The good draft established by the many holes in the basement probably saved the inhabitants from potential CO poisonings. Too many holes and you'd kill the draft on the actual appliance flueI know - I test with a draft gauge
"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."
Howard Thurman
Too many holes in the basement walls would kill the draft? Or are you referring to the chimney? Ah, I don't think I was clear enough! I meant to say that the basement walls had lots of holes. That the holes weren't bigger and that the house was still standing was quite surprising after we lifted the poor thing off its old foundation - several above-ground foundation walls fell over once the pressure from above no longer held them in place. One of them was 5" out of plumb over a 5' distance.The rubble foundation below ground was just that, rubble. Any mortar that may have lurked between the stones had long been washed out by water gushing in. Water management in clay soils (here: 14' deep) is one of those things many folk don't seem to think about. At least judging by the sorry state of many foundations around here. On the plus side, the rat slab was easy to remove since there was nothing to it.Our front chimney was OK from a moisture point of view. Even though it was a single-wye (sp?) and much too large for the Williamson furnace firing into it, the low efficiency of the Williamson probably helped keep the chimney reasonably dry. Not much spalling, no big holes. The rear chimney was spall-city, fist-sized holes, etc. A CO disaster in the making. The leaking kitchen DWV above (never fixed even though it and the crack in it was visible!) probably didn't help.
Clean the brick - gently.
Install caps -
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Apply a silane/siloxane-based or similar water repellent (not a sealer, a repellent):
http://www.mfgsealants.com/siloxsea.htm for example.
Jeff
Be sure to remove all of the efflorescence before applying any siloxane, as it will seal in the minerals. I know this, because my DLW paid somebody in my absence to apply siloxane after doing a chimney sweep without asking me about it beforehand.
We had an orphaned flue after we went high efficiency with the heater, and the gas water heater was alone in heating it, hence the efflorescence at the lower area. It also contributed to spallling of the outer bricks. A liner for the water heater solved that.