Thread: Venting gas furnace acceletaes deterioration of flue formerly venting oil furnace?

I rarely see an oil fired appliance, but when writing one up for other problems I noticed this comment, left over from the "canned" comments that came with my report writing software.

"Clay liners that once were used with oil furnaces, and are now being used for venting gas or propane furnaces or water heaters may deteriorate called" Spalling." This is from oil residue absorbed in the liner that breaks down from the gas residue. Because of this potential problem, most chimney sweeps will eventually recommend a liner replacement..."

True, or Urban Inspection Myth?

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When converting from oil to gas, one requirement (at least here in NJ) is to have the liner cleaned. This is to remove the residue and to view the condition of the liner.

Another problem is the size and the venting of the newly installed appliance. If you replace an oil furnace with a fan assisted gas furnace, the chimney may have to be re-lined due to the lower temperature of the exhaust.

I would say to have an HVAC company review it but if you have HVAC guys in your area like mine, they don't know how to size the exhaust.

I had a 6 year old house with 3 appliances (furnace & water heater in basement & furnace in attic) that was raining condensation in the winter. It took 3 different companies before it got resolved.

True, very true. Here in the N east many homes are oil fired boilers with gas water heaters. It dosen't happen in every application but whit the right conditions the condensing gases really screw up the flue.

"Clay liners that once were used with oil furnaces, and are now being used for venting gas or propane furnaces or water heaters may deteriorate called" Spalling." This is from oil residue absorbed in the liner that breaks down from the gas residue. Because of this potential problem, most chimney sweeps will eventually recommend a liner replacement..."

This is a bit of a mis-statement. ALL clay liners are subject to deterioration from flue gases-period. Oil flues undergo significant deterioration, including spalling, softenting, cracks, crumbling, pitting, and falling away without any help from exhaust gases from combustion of NG or LPG. Likewise, the same can be said for these gaseous fuels effects on clay flues.

When a liner, whether clay tile, firebricks, metal or cast, cannot perform its intended function, it must be rebuilt or relined.

When the use of a flue changes to where the flue size and type is no longer suitable for new equipment, the flue must be rebuilt or relined.

When you change fuels, you must have a Level II inspection. While sweeping removes some of the acidic material in a heater flue, it certainly does not remove all or it or neutralize it. If you install an aluminum liner down an oil flue, it will rot away in no time even after sweeping. Sweeping is not cleaning.

So, if you know that upon changing fuels, it needs a level II and the probability of damage to the flue, why wouldn't you call for a liner? It is more of a case of proving it does NOT need a liner than needing one. Since the mortar in the flue joints is not vitreous and is very reactive to acids, the joints will be compromised in almost all cases with heater flues even if the tiles do not appear damaged.
Bob

A supposed authority on chimneys made assertions ( I thinkk in a JLC article)
that every clay liner he inspects is significantly deteriorated.

I inspect several 100+ year old chimneys every week. Many on them I do from the safe vantage point of a flat roof. Sometimes I use a large mirror to shine light all the way down the flue. I am not aware of any flashlight that is as powerful as sunlight.

I rarely find significant deterioration of kiln fired clay tile liners. A second way of knowing the condition of the liner is to open the cleanout at the base. You carefully examine the debris to get an idea how long it has been accumulating.

I have two clay liners and both are in excellent (like new) condition. I switched from oil to gas on both 30+ years ago. One flue (my house is a 2 family) became orphaned 30 years ago and only serves a gas water heater.
(the other is no longer used as I went to high efficiency/PVC 5 years ago)
I see no evidence at the base of any deterioration. I'll ask Santa to take a close up look next Christmas.

Ken, I have two questions for you:
1) Do you only inspect on bright sunny days? 1B)What do you do if a cloud comes over? I'm serious here.
2) If you do not see significant deterioration of the flue tiles yet you find debris in the clean out, then where did the material come from? Part B) how much debris constitutes 'significant' deterioration of the flues. What is the standard rate of deterioration of flue tiles so we can all share in this quantitative measurement.
3) Bonus question: since the average human cannot see joint integrity past the second tile joint( 4 ft. down) how do you fit down in the flue with your mirror to inspect all those tiles including offsets?
4) bonus question 2: Since you stated you inspect many homes 100+ yrs old with flue tiles yet flue tiles were not readily available until after WWI, you "lined" chimneys must have either been rebuilt from the ground up or relined with tile. Since lowering tiles down an unlined chimney is not a recognized installation method because there is no way to insure joint integrity, how can you be sure of all those joints? Not just gaps but protrusion of excess mortar that effectively reduces the flue capacity?

I just trying to make the point that your methods are insufficient based upon current knowledge and technology. I suggest you click on the FIRE Service button on this forum to learn more about inspectioning chimneys. Just some friendly advice.

Please provide a link to the article mentioned so we can read the chimney authority's comments.

Dear Bob Harper,

The following is a brief response to your posting. It is not exhaustive and does not address every minute possibility.

(1) A focused Mag light is useful especially when looking up from a cleanout. I find it useful for the upper 10 feet.

(2) I knew I should have said: <IF you find debris>. I intended some assumptions that I didn’t elaborate for the sake of brevity. (FYI most of our Boston metro bldg. stock is about 90 to 100 years old) The chimneys in economy built houses that were never parged or lined later in life are in poor condition and you will find all kinds of debris at a cleanout, including bricks as well as friable and chunked mortar, etc.

Your first question in #2 should not assume that the debris I was referring to was limited to only masonry. There’s dead animals, beer bottles and cans, cigarette butts and anything that people hanging out on a city roof might toss down. There will be mortar that deteriorated before lining and during lining and repairs. Soot from coal and oil fuels and maybe even creosote. So, amongst any debris, which I suggested one “CAREFULLY EXAMINES” you would look for scaled liner pieces.

I there is no pile of time accreted debris then the task is simpler and straightforward.
If you find friable dusty stuff and can rule out mortar then it might be clay liner but I doubt it falls away and down the flue as a fine powder.

Most home inspectors try not to make QUANTITATIVE STATEMENTS and prefer the “safety” of QUALITATIVE statements. I rarely make quantitative statements to clients unless we are one on one with no witnesses present. And I am careful as to how I quantify in my rpt. So you won’t find any quantification in my post—Just the word SIGNIFICANT which is a great CYA word.

Michael Thomas’ original post was about “ACCELERATED DETERIORATION CAUSED BY PRODUCTS OF COMBUSTED GAS “ and I was simply offering my observations from a common sense approach. We have had a lot of conversions from oil to gas in Boston since the 80’s, due to the gas companies giving away heating equipment to owners who switch from oil to gas. You moved the topic to one that is of greater concern when you mention “joint integrity” and “flue capacity.”

Joint integrity and flue capacity are a greater concern with a flue serving a wood burning appliance or frpl. If you know of any links to reports of actual incidents where clay liners that were not perfectly stacked and mortared were the cause of some serious incident in FLUES EXCLUSIVLEY SERVING GAS APPLIANCES please follow up and post them so that I and others who are not concerned over these defects may change our minds.

(3) In the last sentence of my post I whimsically infer that my observations of the flue are very limited. That is why I previously recommended examining what may lie at the base of the chimney. It is indeed difficult to lower 2 ft liners on top of each other.
I see variations in the skill and have never seen a perfect job on a chimney lined later in life but I don’t worry if its serving a gas appliance but will report shoddy work on a flue for wood burning. In my state we do not have to look up or down flues. So, I have some latitude as to how I approach this matter.

I spent a lot of money to attend Dale Feb’s FIRE seminar and have his book.

I just examined my orphaned flue (30 yrs) and found only a few spider webs and a lady bug at the cleanout. From my limited vantage points I see absolutely no change or any form of deterioration. So, the only thing I worry about regarding the conversion from oil to gas is how much will the gas cost in the future.

Originally Posted by Ken Bates

...(1) A focused Mag light is useful especially when looking up from a cleanout. I find it useful for the upper 10 feet...

Say what now? The Mag light is "especially useful" for the upper ten feet when looking up from the bottom?

John Arnold,

You are quoting out of context. Re-read the posts and decide if you want to make a fool out of yourself. See Item #3 in Barker's 6th post.

Ken

Originally Posted by Ken Bates

John Arnold,

You are quoting out of context. Re-read the posts and decide if you want to make a fool out of yourself. See Item #3 in Barker's 6th post.

Ken

Ken:

1) I've made a fool of myself before and survived.

2) Who the heck is Barker?

Originally Posted by Bob Harper

... 3) Bonus question: since the average human cannot see joint integrity past the second tile joint( 4 ft. down) how do you fit down in the flue with your mirror to inspect all those tiles including offsets?
...

Ok, ok. I guess Bob Harper is "Barker". Do we have to call him that from now on? So his #3 is quoted above. How does that make it reasonable to claim you can inspect the top 10 feet of a flue liner from the cleanout with any kind of illumination, much less a Mag?

I never made any claims.

Somebody other than myself is stating I fit myself down the upper ten feet of a chimney.

If you want to be a pain in the derriere and continue I will put considerable more time and effort into this.

Ok, ok. I guess Bob Harper is "Barker". Do we have to call him that from now on? So his #3 is quoted above. How does that make it reasonable to claim you can inspect the top 10 feet of a flue liner from the cleanout with any kind of illumination, much less a Mag? ( Bob Barker was a TV host)

This nit-picking stuff is really not worth the effort but what the heck. I’ll regard it as keeping up my typing skills and speed.

The following (1) just below is my response to Bob Harper’s BONUS QUESTION #3 and his #1 question

(1) A focused Mag light is useful especially when looking up from a cleanout. I find it useful for the upper 10 feet.

I would have been a bit more clear if I had wrote --- is especially useful --- instead of “is useful especially” in the first sentence. Nonetheless especially is a modifier for the word useful. It means that is more than just useful, it is especially useful. In the very next sentence I state: “I find it useful for the upper 10 feet.” The meaning, although subtle is that (the Mag light) is not as useful when you are on the roof with lots of ambient light. So the two sentences relate; and implicit, although not explicit to some people, they are a way of comparing means of illumination. Remember this was part of a response to Bob Harper’s question (directly below) about what I do when I lack sunlight.

“1) Do you only inspect on bright sunny days? 1B)What do you do if a cloud comes over? I'm serious here.”

I didn’t feel like fully responding to Bob’s 3rd BONUS question as I considered it just kind of smart-assed and inane.

Indeed I could have been more explicit but the topic was not a critique about how to visualize the interior of flues. I was too casual and ass-umed that readers would understand what I intended to convey.

Some kind of short circuit interjected Bob Barker ( Host of a popular TV game show )

Harper
Barker 4 out of 6 letters (brain cancer or too many Margaritas)

Ken,

Would you finish filling out your User Profile. location, occupation.

Thanks,

Originally Posted by Ken Bates

I considered it just kind of smart-assed and inane.

(brain cancer or too many Margaritas)

Or, like you consider Bob Harper's post, maybe your post was just simply (to use your words) "kind of smart-assed and inane.".

Sure seemed that way to me, anyway.

Originally Posted by Ken Bates

Michael Thomas’ original post was about “ACCELERATED DETERIORATION CAUSED BY PRODUCTS OF COMBUSTED GAS “ and I was simply offering my observations from a common sense approach. We have had a lot of conversions from oil to gas in Boston since the 80’s, due to the gas companies giving away heating equipment to owners who switch from oil to gas. You moved the topic to one that is of greater concern when you mention “joint integrity” and “flue capacity.”

Joint integrity and flue capacity are a greater concern with a flue serving a wood burning appliance or frpl. If you know of any links to reports of actual incidents where clay liners that were not perfectly stacked and mortared were the cause of some serious incident in FLUES EXCLUSIVLEY SERVING GAS APPLIANCES please follow up and post them so that I and others who are not concerned over these defects may change our minds...

I just examined my orphaned flue (30 yrs) and found only a few spider webs and a lady bug at the cleanout. From my limited vantage points I see absolutely no change or any form of deterioration. So, the only thing I worry about regarding the conversion from oil to gas is how much will the gas cost in the future.

Ken,

At least in my climate the greatest practical concern with liner joint integrity in oil to gas conversions is the migration of moisture from the increased condensation within the flue through the gaps between liner sections and into the chimney structure above the conditioned space, deteriorating the chimney structure in attics and above roofs.

Absolutely no question this happens in cold climates, and here in Chicago we see it all the time.

Occasionally this deterioration is extensive enough that you can see through to daylight from inside the attic via a deteriorated chimney (of course, this is much more likely in an unlined chimney - and we have plenty of those here, too). I've never put a CO monitor on such a breech, but I would assume that in some case there will be some leakage, especially if there is also partial restriction or obstruction above this point.

And while I have never read and account of injury or property loss (other than the cost of lining/rebuilding the chimney, or damage directly related to a chimney fall) as Bob Harper points out the reporting system for such events is poor and the results are poorly disseminated, so in this case IMO "the absence of evidence is not evidence of absence".

I should stay out of this but ... I don't care what the clay liner looks like. Install a liner for the new furnace or HWT. Beyond the condensation issues due to size and temp, the real issue is safety.
The majority of old clay liners I see look great. Minor to moderate deterioration, no big deal. I can (always) tell when the clay liner is going to look bad. If the chimney bricks above the roof are spalling, the chimney cap is in bad shape or missing and there's no doghouse the top sections of liner are going to look bad. Water into the basement wall and the bottom sections will look bad.
Focusing on the liner is nonsense. The clay liner is not the weak point in the system. It's the joints between the sections that are the weak point and the hazard location. They are always deteriorated, gone, open, etc. Therefore it is new liner time.
Mr know-it-all Seller was pissed that I essentially put this into a report for an HI. Client really wanted the house and the whole thing became an issue. Mr know-it-all Seller swore I was an idiot and didn't know a damn thing. His clay liner was perfect, he inspected it himself. I love proving those guys wrong.
I duct taped my camera to multiple 1x4's screwed together for length and lowered it down through the chimney taking pictures of the joints. I used a length and pieces of 1/2" conduit to press the button. The pictures that came out showed almost all of his joints mostly or completely gone.
I usually just check a few feet up or down as possible. It's always the same, joints are shot. Sometimes I can see the openings in the attack or basement (once I move the crap out of the way).

Markus Keller's and Michael Thomas' post were useful and thought provoking.

I will certainly give more thought to joint integrity.

If sand were packed between the flue and inner wythes of the chimney bricks then water would easily get to the mortar. And of course flues are never truly isolated. I think most of the rainwater or acidic condensate that travels between the joints will cling to the outer surfaces of the liners and dribble to the base of the chimney. (Ever try to pour the contents of a cup or glass slowly or even moderately to another container?)

But there will be gobs of mortar and the occasional rusted steel nail that some masons used to bridge the gaps from brick to liner.

Originally Posted by Ken Bates

--I think most of the rainwater or acidic condensate that travels between the joints will cling to the outer surfaces of the liners and dribble to the base of the chimney.

.
Even if that theory were true.

As the joints deteriorate the Gas Exhaust then travels through the Gaps ,fills the void with corrosive acid & moisture '

As stated this leads to " ACCELERATED DETERIORATION CAUSED BY PRODUCTS OF COMBUSTED GAS. "

That's more than a Nick or a Pick. But the Point itself.

Ken, my questions to you were legitimate and based upon professional chimney inspection practice. For instance, for years, Tom Urban has brought around his 15ft. horizontal chimney mockup, invited sweeps to inspect it from both ends, then opened it up to show what they missed and how you can see them with his Chim Scan cameras. It is a simple matter of geometry that you cannot get the angle to see what needs to be inspected. No need for personal attacks or unprofessional nasty comments. You made assertions on inspections that go against current knowledge and practice.

As for your acidic water theory, bear with me on this: acid + base= salt + water. As acids attack the alkaline mortar, it is converted to sand and salt water. Moisture will condense on both sides of a flue tile. Rain is driven through the outer face of brick by vapor diffusion until it hits a capillary break such as the 1/2-4" gap surrounding the flue tiles. There, the condensate will attack the mortar and weep down eating up the chimney from the inside-out. There will be some condensate on the outer wall of the tiles, too. Down near the breeching, the water will tend to soak in. As the unit fires, you can get steam cracks. Also, once a joint is gone, the ends of the flue tile, which are not vitreous, will sponge in moisture easily where it can lead to cracked/ flaked tiles. All it takes is a pin hole.

Ken, dialogue is good. Just please try to contain your passions and stick to defensible facts and no nasty comments please. Have you found the link to the article you mentioned in your first post? I'd really like to read it.
Thanks in advance,
Bob

I can't find anything that was nasty or vitriolic in my responses. And I did not intend to be nasty.

However, I perceived posting some questions as BONUS questions to be CONDESCENDING. So that is why I said KIND of smart-assed. Note that I used the word KIND which modifies smart-assed and even suggests that they may not be smart-assed (SEMANTICS).

So, I can't see where I was out of line or ascerbic. But I can see that I have a lot more to learn and understand vis a vis chimneys and I have learned something from these posts and I think that you and other posters in this thread do have good insight into the topic.

I would also like to point out that I never refuted or contradicted anyone opinions or observations. I just offered my own observations and never stated that my observations reflect what occurs in general.

PS: I bear no animosity and am not interested in playing one-upmanship games. I am comfortable with my knowledge and lack of it and am not out to prove anything.

Sincerely,

Ken Bates

Originally Posted by Ken Bates

--I have learned something from these posts

Ken,

That's why most of the people are on this board.

Most of us are willing to learn.

Look forward to your Points of Views.

Checkout NFPA 211. Stainless Steel all the way; The corrosive nature of Oilwill make short work of any clay liners.