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New Furnace and Flue with corrosion after 2 weeks


dalmat36
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I recently had my oil furnace and ductwork replaced in my home after my existing furnace malfunctioned and filled the entire house full of white smoke. I am concerned because my flue seems to have white corrosive growth and water coming out of the seams of the metal and on the inside of the flue. I have attache photos showing the corrosion after approx 2 1/2 weeks of use. I had my chimney cleaned by a local chimney sweeping company and expressed concern of the corrosive growth and they don't seem to think this is a big thing to worry about however I am a little skeptical after ready a few articles online. I was told my chimney does not have a metal liner but rather is made of clay. If I am looking at a potential problem in the near future I would like to have this fixed immediately rather than waiting until damage is done. Am I over worrying about the water and corrosion or should I find a different contractor?

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Pictures usually don't appear because of spaces in the file name.

The white deposits are probably from condensation. It's a sign that combustion byproducts are cooling in the vent connector or in the vertical chimney flue too soon. It can be from a number of reasons. One possibility is that the new furnace output is cooler than the previous, requiring a smaller chimney flue so that the exhaust rises to the top of the chimney before cooling.

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Pictures usually don't appear because of spaces in the file name.

The white deposits are probably from condensation. It's a sign that combustion byproducts are cooling in the vent connector or in the vertical chimney flue too soon. It can be from a number of reasons. One possibility is that the new furnace output is cooler than the previous, requiring a smaller chimney flue so that the exhaust rises to the top of the chimney before cooling.

The furnace I had installed was rated at 85% efficient oil furnace as compared to the older one which was 78%.

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Pictures usually don't appear because of spaces in the file name.

The white deposits are probably from condensation. It's a sign that combustion byproducts are cooling in the vent connector or in the vertical chimney flue too soon. It can be from a number of reasons. One possibility is that the new furnace output is cooler than the previous, requiring a smaller chimney flue so that the exhaust rises to the top of the chimney before cooling.

Yes, I measured the flue pipe prior to the transition piece to be 5" dia. and the metal piece in chimney is 6.1" dia.

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Pictures usually don't appear because of spaces in the file name.

The white deposits are probably from condensation. It's a sign that combustion byproducts are cooling in the vent connector or in the vertical chimney flue too soon. It can be from a number of reasons. One possibility is that the new furnace output is cooler than the previous, requiring a smaller chimney flue so that the exhaust rises to the top of the chimney before cooling.

Another possibility is that the furnace is too large. The resulting short cycles don't allow the flue to fully warm.

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I'll bet that:

1. not only is the furnace more efficient but, the firing rate is less.

2. the chimney is located on the exterior of the building.

As has been stated, condensation is occurring inside the flue. The flue will need to be made smaller and easier to heat. This will involve the installation of a properly sized stainless steel liner inside the masonry chimney.

As Jim Katen mentioned, make sure that the furnace is not short cycling.

Tom Corrigan, Ret.

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The vent connector is very long with several elbows. Combine that with the increase in it's dimension, prior to the termination at the vertical chimney flue, is likely the primary cause of the condensation. (Do the horizontal sections slope the right way?)

They probably put the sealant and tape on the joints of the vent connector because combustion byproducts, having already cooled before rising up the chimney, were spilling out. A properly installed natural-draft vent system needs nothing added to the joints and nothing leaks out.

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The vent connector is very long with several elbows. Combine that with the increase in it's dimension, prior to the termination at the vertical chimney flue, is likely the primary cause of the condensation. (Do the horizontal sections slope the right way?)

They probably put the sealant and tape on the joints of the vent connector because combustion byproducts, having already cooled before rising up the chimney, were spilling out. A properly installed natural-draft vent system needs nothing added to the joints and nothing leaks out.

Here I go agreeing with the home inspector again! [:-bonc01]

The first piece of pipe after the 90 coming out of the furnace is running down hill,then it looks like its running flat to the next 90.

Then it must start climbing at some point to hit the chimney going out.

Why didnt they take and spin the furnace 90 degrees when they installed it to atleast cut down on the offsets?[:-weepn]

With that many offsets its no wonder they needed that big of a flue pipe to vent it,but by the time it reaches the chimney im suprised it has enough force behind it to properly vent! [;)]

And as far as the aluminum tape on the flue pipe it must be to keep all the condensation from dripping out of all the joints in that flat/reversed sloping pipe! [:-yuck]

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Here I go agreeing with a contractor but,

Note also that the minimum required clearance between the single wall smoke pipe and the plastic condensate drain, the plastic plumbing waste pipe and (if the code guy is on his game) the combustible refrigerant tube insulation is required to be at least 18"!

You will need to install a type L smoke pipe and/or change to non-combustible pipes and insulation.

Tom Corrigan

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Here I go agreeing with a contractor but,

Note also that the minimum required clearance between the single wall smoke pipe and the plastic condensate drain, the plastic plumbing waste pipe and (if the code guy is on his game) the combustible refrigerant tube insulation is required to be at least 18"!

You will need to install a type L smoke pipe and/or change to non-combustible pipes and insulation.

Tom Corrigan

Thank you all for you posts as they have been very helpful. I have contacted a local inspector and he mentioned that as of 2004 my contractor was required to obtain a permit to replace the furnace and duct work which would have required a inspection prior and after the installation. I suspect the contractor has not obtained the proper permits since I have not received any information about a permit and no code inspection was done prior to the work being started. I'm going to contact my local code office monday to schedule an inspection and find out if any permits were obtained.

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Note also that the minimum required clearance between the single wall smoke pipe and the plastic condensate drain, the plastic plumbing waste pipe and (if the code guy is on his game) the combustible refrigerant tube insulation is required to be at least 18"!

Tom Corrigan

Some newer oil fired units have a requirement for only 9 inches clearance from the single wall flue pipe.

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  • 2 months later...

First things first guys, this is an oil furnace which requires tuning to set the air fuel mix and dial in the stack temp to ensure condensation doesnt occur in chimney. The first thing that should be done is a combustion analisys by an oil tech and make sure the burner is set up properly. Oil is not like a gas unit ( plug and play) it must be tuned up annually. One can make many adjustments from O2 levels, oil pressure, and oil flow rate, all of which affect stack temps therefore the potential for condensation. I wont touch an oil burner without performing combustion analisys.

Or could be rain water infiltration

Install notes; the exhaust/ flue piping MUST always have a positive pitch, yours does not and this is a major concern! around here its against code to add sealant or tape to metal flue piping as its not needed therefore is used to conceal a problem.. Get a good oil tech out to inspect/correct installation.

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