Furnaces, Moisture, Acid and Your Flue

The furnace flue is the often forgotten part of your chimney and many consumers are surprised when serious problems are found within it.  Years of service can take their toll on the flue especially when you consider the extreme conditions the flue typically endures.  Here is a brief overview of what your furnace flue must do and the challenges it faces:

Oil Boilers/Furnaces:  Oil exhaust has a very high sulfur content, and when combined with moisture forms sulfuric acid which can very quickly damage and destroy most flues.  Clay flues will tend to flake apart (called spalling), joints erode, holes form, and serious carbon monoxide problems become much more likely.  The moisture itself can come from rainwater entry into an uncapped flue, or the moisture can be a byproduct of combustion in a high efficiency furnace or propane appliance.  In the latter case the moisture condenses in the flue before being exhausted outside either due to a cold chimney, infiltration air leaks, or an uninsulated/poorly installed liner.  Whatever the source, this moisture/sulfur combination can create havoc in as little as a year.  Some furnaces simply MUST have a good quality stainless liner installed to function safely.  In one recent case we came across a high efficiency System 2000 oil furnace which was installed without a proper stainless liner (which goes against the installation requirements) and one year later it had destroyed the flue to a point where the furnace would no longer run and posed a serious threat to the occupants of the home.  The System 2000 is a GREAT oil system, but must be installed properly.  Please consult your local dealer or Energy Kinetics for more information.

Propane Appliances:  In addition to rainwater entry as described above, the additional problem propane appliances have is the inherent moisture content of propane itself – propane burning produces a lot of water in the exhaust.  This water when vented into a traditional masonry chimney, especially one outside the envelope of the home, will condense and create many similar deterioration issues.  Spalling, erosion, etc can occur to a point where the flue can no longer contain the products of combustion.  Insulation is sometimes required when relining a propane flue to keep the exhaust gases warmer to avoid condensation within the chimney.

So what should you do to protect yourself?

  • 1.  Have your flue checked regularly, as part of your routine maintenance.  We, as well as many other certified sweeps, will gladly check the flue condition when we’re on site to sweep a wood flue.  (BTW, the same service guidelines apply to oil and gas flues:  Checked once a year, cleaned as needed.)  Often we will want to clean, inspect, and scan the flue if we’re on site for the first time to get a good baseline.  After that, we’ll check it during your yearly service to keep track of it’s condition.
  • 2.  Install a cap!!!  A $70 cap can save you thousands of dollars of repairs down the road, as well as prevent injury to you and your family.  If you are the DIY type, you can get a cap of your own and install it.  It’s not that hard.  My only suggestion is make sure the cap is a minimum of 316 stainless steel, otherwise it will just fall apart in the acidic environment of an oil flue.
  • 3.  Line your flue if necessary.  In addition of a possible bump in efficiency of your appliance, you will have a much safer chimney.  Be sure to insulate if necessary.
  • 4.  If you’re replace your furnace or boiler with a newer unit, remember that often a proper inspection of your chimney is required by code.  Simply looking up the flue is not nearly enough.

So there it is folks.  As always, feel free to contact us via the web or phone if you have any questions, and please enjoy the nice weather we’re finally having!

First Thing

John RantaJohn Ranta
17:01 22 Mar 24
They arrived on time, worked quickly and showed me the results. Prfessional throughout. jr
william greenwilliam green
23:21 14 Mar 24
Really helped me out can't say enough good things highly recommend!!!! The young man that came to my home was very knowledgeable and friendly great attitude all around answered all my questions and left me stress free best of all left no mess.🤙🏻🤙🏻
Michael Dell'OrtoMichael Dell'Orto
18:39 14 Mar 24
Jaime ConleyJaime Conley
17:13 14 Mar 24
Sarah GilliattSarah Gilliatt
01:46 13 Mar 24
A very thorough and careful job done! Thank you.
Larry CookLarry Cook
15:11 07 Mar 24
I wanted to give 5 stars but they are very busy which meant I had a good wait for both the inspection/cleaning, then for a quote on repairs and then for the repairs. Their prices seemed a little high to me but I have nothing to compare with as they were highly recommended by someone I trust and other companies had plenty of negatives reviews which kept me from getting additional quotes. I am happy with the work and they promptly returned to fix a mistake that had been made. Chris the inspector, Jennifer in the office, and Alex and his repair crew were all pleasant and took the time to answer all of my questions. Alex and his crew even took their shoes off (it was winter) before entering my house without even being asked! So if you are not in a rush and want to ensure you chimney is as safe as possible then I think you'll be happy with Black Moose.
Rebecca DeFuscoRebecca DeFusco
22:35 21 Feb 24
After a recent sweep of our chimney, it was discovered that our flue tiles were cracked. Black Moose techs were hard working, detail oriented and professional! Nice jobs guys! See you next year for my cleaning!
Karen CKaren C
14:52 14 Feb 24
Excellent I highly recommend Black Moose Chimney and Stove; Kelly and Liam are awesome, they did a great job. Extremely professional, arrived early, went through everything with a fine tooth comb ensuring pellet stove was thoroughly cleaned. They also were respectful of my home, conscientious and cleaned up after themselves. Made sure stove worked prior to leaving and told me to call promptly if anything came up afterward. Will definitely use them again.
Denise ClarkDenise Clark
16:32 31 Jan 24
We've had Black Moose clean our chimney for a number of years.But recently, we had an emergency situation at our home involving our chimney & oil furnace flue, which was caked full of soot from a malfunctioning furnace. They came & cleaned out both flues in no time, even going up on the roof with snow on it! They cleaned up after their work in the interior rooms where the oil furnace and the woodstove are located. Great work. Reasonable prices. Very nice people. You can't go wrong with Black Moose.
Joe GJoe G
18:30 24 Jan 24
Goods: The technicians know their business, very efficient in cleaning/inspection along with cleaning up after the 'dirty work'.Others: Communications could be more effective. Despite early coordination about scope of work (multiple flues within same chimney) the estimate provided did not reflect this and the final invoice was significantly more than the estimate provided.Quote for follow-on chimney relining was significantly more than that offered by other companies in the area (and far more than neighbors experienced for similar work accomplished by other companies)