Chimney condensation? Any experts out there?

My hypothesis: Cracked heat exchanger on the Boiler.
Steam/water that should be acting as a hydronic is going up your chimney and leaching out of the mortar between the brickwork.
One way to tell is to fire up the boiler and watch what comes out of the chimney.
”White” isn’t smoke, it’s Steam!
Liner would be a band-aid to the ultimate problem.
 
As someone in the hvac field for many years, I can strongly suggest NOT getting a liner with oil, I've seen many stainless liners fail. They have to be taken out in pieces and chunks, sometimes impossible to remove thus ruining the ability to use the existing chimney.

Understand a chimney is under negative pressure along its length and a few bits of missing mortar between the Tile liner stack is not a safety hazard in an oil flue. It can be a safety hazard in a wood stove flue due to large amounts of flammable creosote that may be deposited; these deposits can seep past the liner and into the chimney structure where, during a chimney fire they can ignite raising the risk of a structure fire. This is the original purpose of a stainless liner and one of the few where they are useful.

It is rare that flue gas condensation alone is the cause of moisture on the exterior of the chimney; It is even more rare that it would occur in an oil burning flue. As has been mentioned, oil exhaust is hotter and drier than NG/propane.

If I had a dollar or two for every chimney I see where a roofer or a chimney professional could not properly flash it I could probably retire by now. Competence is a rare thing.

And in your particular case I can almost assure you that the cracks in the crown and the mortar cracking around the top of the chimney is the most likely culprit for your issue. The reason this almost always shows up more during cold weather has little to do with the flue exhaust and significantly more to do with the fact that the moisture that gets into the chimney from the crown no longer is removed through evaporation into the outside air. This moisture builds and builds and finally starts seeping out of cracks further down in the chimney structure leading to the issue in your attic.

Checking the flashing thoroughly and if there's any doubt hiring a competent individual to flash it properly as well as
thoroughly sealing the chimney with an appropriate polyurethane based caulking and then applying a crown and masonry sealer (there are products specifically for this on the market) to the top and sides of the structure, once complete, would probably give you many years without leaks.

The alternative and the almost permanent way to solve the problem with your chimney in its current condition, although you won't like to hear it, is to tear it down to the roof line and have a competent Mason or bricklayer (I recommend not a "chimney professional") rebuild it from the roof up with new flashing and mortar and a proper poured concrete crown. Please note that finding a good Mason for the small job may not cost much if any more then that liner which will do little for you if anything.
 
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An experienced heating contractor will measure the stack temperature as part of a season check and will consult the appropriate NFPA code on vent type and sizes for this application. Condensation occurs when vent gases cool too much before reaching termination.
 
An experienced heating contractor will measure the stack temperature as part of a season check and will consult the appropriate NFPA code on vent type and sizes for this application. Condensation occurs when vent gases cool too much before reaching termination.
For an oil appliance in residential, an 8/8 tile lined flue is appropriate for 99.99% of everything made since 1940. See my post above, flue gas condensation is not his issue.
 
My hypothesis: Cracked heat exchanger on the Boiler.
Steam/water that should be acting as a hydronic is going up your chimney and leaching out of the mortar between the brickwork.
One way to tell is to fire up the boiler and watch what comes out of the chimney.
”White” isn’t smoke, it’s Steam!
Liner would be a band-aid to the ultimate problem.
If steam...overfill boiler above the top of the sections. If leak above water line it will leak on the floor.

Drive around Albany and Schenectady on a cold day and ya can see who is blowing steam up the chimney. Makes one feel like an ambulance chaser...
 
As someone in the hvac field for many years, I can strongly suggest NOT getting a liner with oil, I've seen many stainless liners fail. They have to be taken out in pieces and chunks, sometimes impossible to remove thus ruining the ability to use the existing chimney.

Understand a chimney is under negative pressure along its length and a few bits of missing mortar between the Tile liner stack is not a safety hazard in an oil flue. It can be a safety hazard in a wood stove flue due to large amounts of flammable creosote that may be deposited; these deposits can seep past the liner and into the chimney structure where, during a chimney fire they can ignite raising the risk of a structure fire. This is the original purpose of a stainless liner and one of the few where they are useful.

It is rare that flue gas condensation alone is the cause of moisture on the exterior of the chimney; It is even more rare that it would occur in an oil burning flue. As has been mentioned, oil exhaust is hotter and drier than NG/propane.

If I had a dollar or two for every chimney I see where a roofer or a chimney professional could not properly flash it I could probably retire by now. Competence is a rare thing.

And in your particular case I can almost assure you that the cracks in the crown and the mortar cracking around the top of the chimney is the most likely culprit for your issue. The reason this almost always shows up more during cold weather has little to do with the flue exhaust and significantly more to do with the fact that the moisture that gets into the chimney from the crown no longer is removed through evaporation into the outside air. This moisture builds and builds and finally starts seeping out of cracks further down in the chimney structure leading to the issue in your attic.

Checking the flashing thoroughly and if there's any doubt hiring a competent individual to flash it properly as well as
thoroughly sealing the chimney with an appropriate polyurethane based caulking and then applying a crown and masonry sealer (there are products specifically for this on the market) to the top and sides of the structure, once complete, would probably give you many years without leaks.

The alternative and the almost permanent way to solve the problem with your chimney in its current condition, although you won't like to hear it, is to tear it down to the roof line and have a competent Mason or bricklayer (I recommend not a "chimney professional") rebuild it from the roof up with new flashing and mortar and a proper poured concrete crown. Please note that finding a good Mason for the small job may not cost much if any more then that liner which will do little for you if anything.
This makes sense to me except that the roof is brand new, and the flashing has been replaced 3 times in 3 years, thinking that was the issue (and each time the person that did it said the flashing looked fine).

And the cracks makes sense too, but it happens when it’s not wet out. Every single day when it’s cold out. Yet not at all in summer months and the rainiest summer we’ve ever had here. But I think you’re right, the chimney needs a sealing, a crown and repair. I just am concerned that for some reason (maybe condensation inside the flue) it’ll still be leaking inside the plywood in the attic. And it’s more focused on one side - the side that does have a cap over it - and it’s the side of the fireplace, which we don’t use anyway. Might heat from the oil furnace side be getting into the fireplace flue and condensing in there? Either way, I do agree that the chimney needs repair up there. And good luck to me for finding someone now. I can’t expect anyone to show up in winter. plus I don’t think mortar will dry in freezing temps.
 
How far does $3100 for the liner and cap, or mortar repair, go towards a more efficient condensing boiler that can be vented out of the side with PVC and save you $$ monthly for the next 30 years?
Good question, and I don’t know. If $3,100 solves this problem I’ll comfier that a great investment (well nit great but not the worst thin either).
 
Thank you the replies. I know it’s Christmas Eve, and I’m nit expecting a solution here, just some knowledge, and advice. I’ll call an expert after the holidays. It’s amazing how lost you can be when it’s not your expertise (and now I understand why people come here for automotive advice so often). My background is automotive, not construction.

here’s a photo of the latest furnace tuneup/inspection. The chimney outside and furnace.
D0187AB6-B3D7-4905-9EE6-45F4E6F46F22.jpeg

446DBF23-BCDB-42BE-BB82-ED44CEF1D172.jpeg

7C96B375-89EC-421C-BE11-4D9D8EB68198.jpeg

View attachment 82008
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How far does $3100 for the liner and cap, or mortar repair, go towards a more efficient condensing boiler that can be vented out of the side with PVC and save you $$ monthly for the next 30 years?
Presumably he doesn't have NG available. That leaves cast iron oil oil or as you mentioned 95% propane. An oil boiler is cast iron, more reliable and lasts longer than a propane unit (~40 years vs. 10-15 for propane condensing) Even at the higher efficiency potential of a propane boiler (and btw this efficiency advantage evaporates with return water temp over ~130, i.e. baseboard) you will burn 1.3 to 1.4 gallons of propane to every gallon of heating oil due to the lower BTU per gallon. Your maintenance advantage over oil also evaporates as 95% will require annual maintenance and often a maintenance kit every year.

On top of all that, he will still have the chimney structure and leaks to deal with.

As he mentioned much of the leakage is on the fireplace side, this is clearly not due to condensation and most importantly if you look at the stack temperature he has a stack temperature of over 500 degrees which is not going to present a condensation issue in that flue.

In fact with a stack temperature that high it tells me that either the boiler has not been brushed down in a long time or it's probably being over fired for the application and could stand to be down fired quite a bit for his home - it would save him a lot of fuel.

Masonry will absorb a lot of moisture before it releases it this is why this wetness and these leaks may not correlate directly with weather events also as I mentioned in cooler weather moisture that does enter the deteriorated chimney will not evaporate as quickly from the structure it will instead leave out of other cracks and crevices and into the Attic
 
I don’t know a thing about boilers as most homes here are forced air natural gas for heat. I had a multi family building with 4 natural gas boilers but the property manager dealt with them. I figured an efficient natural gas (if available in his locale) boiler could be vented out of the side of the basement with PVC like they do here with furnaces and skip the chimney altogether. BituminousCoal seems like he is in the industry so I’ll defer to him. I agree 500+ degree flue temps should not cause any condensation.
 
I've been thinking about this. There must be a logical explanation.

I wonder if the upper bricks and mortar are accumulating water in the non heating system from rain water coming down the chimney. Then when the heating system begins, with the high temperatures being generated, some water vapour is driven through the cracked mortar and onto the plywood. And because the rest of the mortar is in generally good shape you don't see staining on the rest of the outside.

If I'm right, the solution would be to stop rain water running down the chimney. In which case you need a good rain cap. But then again I have no expertise with chimneys (and some of my relatives would say with anything else either).

A rain cap would be a relatively low cost experiment. My ceramic rain cap (which I'm told is better than a metal cap) cost a couple hundred bucks.
 
Often a chimney will sweat...or get wet on the outside from condensation....warm moist air against a cold chimney... and with all that thermal mass the chimney temp will always lag behind outside ambient....so plywood against chimney means plywood temp will follow chimney temp. Add moist air in a poorly vented attic space against cold plywood...

A masonry chimney runs cooler than one might expect on the outside depending on stack temp.

...outside chimneys suck..

...and circs on that boiler should be on the supply side and not on the return....processes air much better that way..
 
Often a chimney will sweat...or get wet on the outside from condensation....warm moist air against a cold chimney... and with all that thermal mass the chimney temp will always lag behind outside ambient....so plywood against chimney means plywood temp will follow chimney temp. Add moist air in a poorly vented attic space against cold plywood...

A masonry chimney runs cooler than one might expect on the outside depending on stack temp.

...outside chimneys suck..

...and circs on that boiler should be on the supply side and not on the return....processes air much better that way..
That section of my attic is not vented, and I think it probably needs to be. The rest of the attic has ridge vents. That section has nothing but the vents on the sides near the gutters. The water definitely is dripping down from the inside. Starts up top and just slowly creeps down. Also there is a huge room bellow that attic space and I know heat loves to go up there. Could it be a situation where I need roof vents installed and maybe insulation installed on that wall?

Here’s a picture of that room bellow that attic space.

CA5924C2-02A0-42D9-BF17-CDD38E2DA207.jpeg
 
As someone in the hvac field for many years, I can strongly suggest NOT getting a liner with oil, I've seen many stainless liners fail. They have to be taken out in pieces and chunks, sometimes impossible to remove thus ruining the ability to use the existing chimney.

Understand a chimney is under negative pressure along its length and a few bits of missing mortar between the Tile liner stack is not a safety hazard in an oil flue. It can be a safety hazard in a wood stove flue due to large amounts of flammable creosote that may be deposited; these deposits can seep past the liner and into the chimney structure where, during a chimney fire they can ignite raising the risk of a structure fire. This is the original purpose of a stainless liner and one of the few where they are useful.

It is rare that flue gas condensation alone is the cause of moisture on the exterior of the chimney; It is even more rare that it would occur in an oil burning flue. As has been mentioned, oil exhaust is hotter and drier than NG/propane.

If I had a dollar or two for every chimney I see where a roofer or a chimney professional could not properly flash it I could probably retire by now. Competence is a rare thing.

And in your particular case I can almost assure you that the cracks in the crown and the mortar cracking around the top of the chimney is the most likely culprit for your issue. The reason this almost always shows up more during cold weather has little to do with the flue exhaust and significantly more to do with the fact that the moisture that gets into the chimney from the crown no longer is removed through evaporation into the outside air. This moisture builds and builds and finally starts seeping out of cracks further down in the chimney structure leading to the issue in your attic.

Checking the flashing thoroughly and if there's any doubt hiring a competent individual to flash it properly as well as
thoroughly sealing the chimney with an appropriate polyurethane based caulking and then applying a crown and masonry sealer (there are products specifically for this on the market) to the top and sides of the structure, once complete, would probably give you many years without leaks.

The alternative and the almost permanent way to solve the problem with your chimney in its current condition, although you won't like to hear it, is to tear it down to the roof line and have a competent Mason or bricklayer (I recommend not a "chimney professional") rebuild it from the roof up with new flashing and mortar and a proper poured concrete crown. Please note that finding a good Mason for the small job may not cost much if any more then that liner which will do little for you if anything.
Exactly (had to write this up before grandkids get up for Christmas) First off that crown(we call them caps here) is horrendous, needs tore out and repaired or replaced with a concrete cap or outside cover like stainless but the latter is overkill. The cover/cap on the one flue is great BUT the water runs off into the other flue which is not covered and will also cause damage. Get 2 individual caps or one large double for both. From what I can see when I blow up the photo is the flashing on the one corner sticks out a little could be the photo. There is some Efflorescence in the mortar which could be due to water seepage which we know you have. I agree with everything stated by BC above. I could not tell you how many chimneys by Father (mason contractor-old school) tore down due to poor construction and how many bad flashing jobs are seen in construction. give someone and hammer and trowel and a pickup truck and it makes them a contractor. Last thing that may need to be done depending on the hardness of the brick. Some brick is not baked as hard as others so I would pressure wash the brick then put a sealant on it. I am not talking about Thompsons--go to a masonry supply house and get the commercial stuff. Grandkids coming down stairs--time to enjoy them. Good luck and Merry Christmas.
 
If there’s no venting except the soffits, you aren’t getting much, if any ventilation up there. I’d say a ridge vent would be a great idea since you can’t have a gable vent with the chimney in the way. Some ventilation and correcting the top of the chimney would go a long way to fixing the problem I imagine.
 
That section of my attic is not vented, and I think it probably needs to be. The rest of the attic has ridge vents. That section has nothing but the vents on the sides near the gutters. The water definitely is dripping down from the inside. Starts up top and just slowly creeps down. Also there is a huge room bellow that attic space and I know heat loves to go up there. Could it be a situation where I need roof vents installed and maybe insulation installed on that wall?

Here’s a picture of that room bellow that attic space.

View attachment 82114
More importantly a vapor barrier along with attic venting. That chimney needed to be built on the inside warm space with no part of the chimney outside in the cold.
 
Well, a couple updates. Freezing rain here today and went up there today and it was worse. So, I think the suggestions of a rebuilt crown and cap are probably in order. Maybe some vents installed too. So apparently the moisture was wicking out even when it wasn’t raining? Can’t believe that could happen, but it looks like it was/is.
 
Well just a little update, finally was able to get someone to come out. He said there were two holes at the flashing, nails that were removed and not reinstalled during the roof replacement. He sealed them. He also sealed some brick and the cracks at the top, temporary repairs. He said the flue in the oil burner side had a tile that had shifted and suggests a liner install. Also a stainless steel cap. Thoughts on the liner? I'm hearing conflicting things...safety get it done...not a problem half the chimneys in America have shifted tiles it won't be an issue with oil heat, if it were a wood burning stove I'd be concerned. The guy said technically it's a fire code hazard but that he couldn't tell me if it would ever be a fire issue. He said the side of the chimney was stained pretty badly because of the leaking/shifted tile. Said he could probably do the liner for $2,500...or a cheaper one for a grand. And the cap would probably run $300 and wouldn't charge me to install it. This guy seemed very very reasonable.

I'm leaning towards doing it.
 
I would recommend not getting a liner for your oil flue, it serves no safety purpose and even the best 316 stainless will fail in the future causing you more problems that you would not have.
 
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