Two more questions about furnace heat exchanger

Stan in Oly, WA · Oct 31, 2014

A few days ago I posted a question about the recent inspection of my natural gas furnace. I got a lot of very good information about it, for which, thank you very much. The fundamental question, of course, is one which it is not possible to answer: When is the heat exchanger going to fail?

Yesterday I was finally able to speak with the tech who did the inspection. I don't think he said anything which wasn't true, but he also didn't say anything which wasn't part of a sales pitch. Now, all I really know for sure is that I have a furnace which is more than 20 years old, and the heat exchanger could fail. That does me about as much good as knowing that I could be in a car accident someday.

Here are my two new questions: Are catastrophic heat exchanger failures which cause fires common events? I know that some here will say that even if the odds are only one in a million, I owe it to my family to stop using the furnace immediately. But if we never did anything that had one in a million chance of resulting in an accident, we'd never drive a vehicle, climb a ladder, etc. So I'd like to know the answer and use the information to make my own decision.

The other question is, how easy is it to view the heat exchanger? I took the front panels off the furnace this morning and it appeared to me that you would have to remove a major component with lots of wire and hose or pipe connections to get a look at the heat exchanger. Not that a furnace tech couldn't do this, of course, but it looked to me like it would be moderately complicated and time consuming.

Thanks,

Stan

Tom in TN · Oct 31, 2014

Stan,

I'm not a furnace guy and I have no new information for you. But, just along the same lines. I sold a house that was about 8 years old. The prospective buyers had a house inspector go through the house before they committed to buying it.

He went nuts. The heat exchanger in the furnace had to be replaced. The air conditioner compressor had to be replaced. It needed a new roof. All of the insulation in the floor joists in the crawl space needed to be replaced. The electrical outlet on the deck needed to be replaced. And other stuff that I can't remember right now.

I told the prospective buyers that they should do what they think is right, but that I wasn't going to do a thing about the items that the inspector stated except, I had found a loose wire that had been pushed into the back of the outlet on the deck. I curled the ends of the wires going to that outlet and put them under the screws.

There was nothing in the world wrong with any of those items.

Good luck on your decision on the heat exchanger.

Tom in TN

PS. The prospective buyers bought the house and were very happy with it.

John,PA · Oct 31, 2014

I will try to give some personal (experienced) answers:

1. If I received the furnace (news) that YOU did, I would probably "shelve" the information until I personally saw what the technician saw.
A. To protect my "liability" I have to tell and show the owner something, just in case.
B. As a HVAC technician, myself, non-state license, though...I would just be honest to start with. EX: Ask the technician what HE would do about the situation?

2. Find out if a new heat exchanger is available for your make, model, s/n of gas appliance. Usually less expensive than furnace replacement and duct work transitions

3. I assume the heat exchanger is NOT stainless steel.

4. Again, from the info. that you provided, I would still NOT worry about a "what-if".

As a coinincidence, my daughter who lives in CO just called me. New house, 7 yrs. ago. ALL new utilities and appliances, etc. including gas furnace (HEIL)with central A/C.

2 days ago a hvac tech. said more or less the same thing to her. He was called to check-out the system. He said "your system is about worn out". Your a/c operates on R_22 which makes the system obsolete.
The Tech. gave the daughter a quote of $7,000.00 to replace the entire system.

My remark to the daughter: Show me a bad heat exchanger (PICTURE). We have "direct drop-in refrigerant for the R-22. DuPont stuff.

So far I convinced her NOT to seek re-financing the house for the $7,000.00

You take it from here.

HTH John,PA I have a new boroscope camera.

Tramway Guy · Oct 31, 2014

Had a heat exchanger fail on an oil furnace. Puff of smoke into the house when the burner started up. I wired the circulating fan so that it came on as soon as the furnace turned on instead of waiting to heat up. This kept the fumes in the firebox. Not recommended, of course, but kept us warm till new furnace got in.
I think heat exchanger failures would seldom be catastrophic. Small holes at first, maybe a crack. If they had a habit of catastrophic failure, they couldn't get UL or CSA listing.

John,PA · Oct 31, 2014

PS: The governing agency for your information is the NATURAL GAS CO.

You can always call the GAS CO. They can dispatch a personnel to check out your furnace system. If found a potential "HAZARD" they have the right to "RED TAG" the system.

John,PA

JDemaris · Oct 31, 2014

My heat exhanger in my oil hot-air furnace got a hole burnt through the steel after that refractory blanket fell apart. The heat exchanger is just thin mild steel and uses the blanket to protect it from burn out. The result was we had fumes in the house and the burner-flame did not fire properly. I took the burner out. I welded in a patch where the hole was. I then put in a new refractory chamber that cost $60. That was 10 years ago. No issues since.

How the heck does anyone claim a bad heat exchanger can start a fire? From dust igniting in the heat ducts?

dpendzic · Oct 31, 2014

ask the tech how he determined the crack. the odds of dying in a car accident are about 1 in 4000, of dying in a fire are around 1 in 1300
-after 51 years of fire fighting with numerous furnace and boiler fires we never had one that caused serious injury to the occupants, but did total a few homes.--- and co alarms alert you to minor co levels--make sure you have one.

Stan in Oly, WA · Oct 31, 2014

It took me a moment to figure out what the figures 1 in 4,000 and 1 in 1,300 meant. Has to mean one death per 4,000 car accidents and one death per 1,300 house fires, right?

I'm not actually worried about my furnace killing me or my wife or our dogs even if it does develop a heat exchanger crack because we don't run it after we go to bed or while we're away, and we do have a CO monitor/alarm, as well as several smoke/heat alarms. My main concern is to avoid a situation where CO poisoning is possible, CO detector notwithstanding, as well as to avoid damage to my house, or to the furnace itself.

Thanks, Stan

Stan in Oly, WA · Oct 31, 2014

I've been doing a lot of reading about it lately, as you might expect, and here's what I've read about heat exchangers starting fires. If one is unfortunate enough to own a furnace more than 20 years old, but also 90% or more efficient, as I do, then you can have a situation where a hole in the heat exchanger can cause the flame to reverse direction because some characteristic of the enhanced efficiency components can cause the air pressure outside the exchanger to be higher than inside, and there is no high temperature emergency gas shutoff because they weren't installed on furnaces manufactured then. This may not be precisely accurate---a couple of days' research hasn't made me a furnace expert---but it's something like that.

Stan

MarkB_MI · Oct 31, 2014

I would install an CO detector in the sleeping area of your house and not worry about it. We've had to have furnace inspections at a couple of our rental houses (local ordinance) and one had a crack. We went ahead and replaced it even though the guy who found the crack said there was no measurable CO entering the ducts. In other words, your HVAC guys prediction it will fail doesn't mean you're in any immediate danger.

MarkB_MI · Oct 31, 2014

No need to use an R22 replacement. R22 is very much still available and at reasonable prices.

kevinj54 · Oct 31, 2014

Pretty much all 90% are INDUCED draft and have pressure switches to prove draft.

I have not read this all the way thru but in general if the heat X cracks the inducer will not be able to prove the air switch to energize the ignition circuit.

What brand & model furnace is it?

John,PA · Oct 31, 2014

I know.....R-22 is cheaper now than ever. They tell me "until supplies run out!" I just bought a couple of 50 pound cyls.

I ain't in any hurry to change over our cold storage systems, yet! I always wait 'till they are empty of R-22 for some reason.

John,PA

da.bees · Oct 31, 2014

Stan heat exchangers are slippery to discuss simply because A. It can have a crack but you can't detect it B. Like everything,quility and luck of the draw has one failing in 10 years while the one next door lasts 40 years.
How common is fires and suffications? I can only recall 2 or three cases where fire department or insurance investigator accused a bad exchanger. Over that same period of time I lost account of space heaters and water heaters investigators pointed to as cause of deaths and property damage. I have personaly detected 4 or 5 dozen 100% undeniable holes. I have suggested or reccomended 2 or 3 hundred be replaced (new furnace,never exchanger)based on collective conditions and circumstances. Those are only ones that didn't involve installing new outdoor ac condensers for economic reasons.
How difficult is it to visualy observe??? Very,and when disassembly of exchanger is required,I don't reccomed it except on commercial units desighned to do so with. There are several reliable tests without putting eyes on the hole.
I understand your uncertainty so my advice is talk to a fire marshall and insurance industry about statistics,not asking "should I replace".
Both have national stats so for grins will you start a new thread if you get them. Meanwhile sleep in the barn if you can rest better. LOL

Stan in Oly, WA · Oct 31, 2014

It's a Payne Plus 90. I think it's 80,000 BTU. We bought the house in 1997, and the previous owner didn't list "New furnace" as a selling point---a good realtor might even make a point of asking the seller about that. That means it's likely to be a minimum of 20 years old.

Stan

Stan in Oly, WA · Oct 31, 2014

Thanks, da.bees. I don't worry about what the furnace will do while we're sleeping because I always turn it off when we go to bed. The weather in the Puget Sound region is very mild. Even in our very coldest weather, it would be unusual for the house to be colder than 50 degrees in the morning after the furnace has been off for seven or eight hours---and not because the house is particularly well insulated, either.

If I can get stats on furnace caused house fires, I will post them in a new thread. I'll have to give some thought to whether I want to bring the situation to the attention of my insurance company---especially since it hasn't actually been established that a situation even exists yet. My heat exchanger could develop a crack in the future? Who couldn't say that?

Stan

PJH · Oct 31, 2014

We had a temporary construction field office in an old rural house, and I was getting some pretty bad headaches every rainy day. I didn't give it much thought until a guy stopped by one day to drop something off, and after about 15 minutes he got real nauseated. In about thirty minutes he was heaving his lunch. He went home and his wife ended up taking him to the emergency room. The next day I looked the place over real close and noticed a slight fan-shaped pattern on the wall above each heat register. (Construction offices don't get the white glove cleaning) Checked the furnace and the heat exchanger was indeed cracked. Long story short - get the CO detector. Mebbe two of them.

kevinj54 · Oct 31, 2014

(quoted from post at 17:23:32 10/31/14) It's a Payne Plus 90. I think it's 80,000 BTU. We bought the house in 1997, and the previous owner didn't list "New furnace" as a selling point---a good realtor might even make a point of asking the seller about that. That means it's likely to be a minimum of 20 years old.

Stan

I worked for a Bryant dealer back then and I am certain that model has many safety's built in.

IF THEY HAVE BEEN TESTED AND ARE OPERATIONAL then it should be plenty safe to use.

Do you a change in the flame pattern when the blower starts???

It is not a real big job to pull the thing apart and check it if need be.

If all is in good shape otherwise just put a new heat X in it.

Many of those 90% units had a lifetime warranty on the heat exchangers.

kevinj54 · Oct 31, 2014

I just read your first post.

Did the tech say the heat exchanger was bad or that it could fail????

Did he test all the safety controls???? Are they working???

If that heat exchanger tested good I would not worry at all due the induced draft it will not fire with a crack big enough to be dangerous. (does the air switch work???)

As someone said earlier maybe put in a CO detector.

dpendzic · Oct 31, 2014

yes--deaths per occurrences but statistics are averages!
Don't feel so safe during daytime hours though--had a restaurant manager die this year from CO poisoning
when he went to the bathroom and passed out.

Stan in Oly, WA · Oct 31, 2014

Kevin;

He said it COULD fail. He said that he could see a white spot or spots on the metal of the heat exchanger which meant that it was ready to burn through. He also said that because of the age of the furnace, there was not an emergency gas shutoff to shut the furnace down if flames started coming out of the heat exchanger. (You can probably understand why I wonder whether this was valuable technical information or a scary hard sell.) I don't know whether he tested all the safety controls. My guess is that he did, because the company he works for has been in business here for decades, and is one of the biggest HVAC companies in this city. I would expect them to do a good job, even if they were also trying to frighten customers into buying new equipment.

Stan

kevinj54 · Oct 31, 2014

(quoted from post at 21:19:20 10/31/14) Kevin;

He said it COULD fail. He said that he could see a white spot or spots on the metal of the heat exchanger which meant that it was ready to burn through. He also said that because of the age of the furnace, there was not an emergency gas shutoff to shut the furnace down if flames started coming out of the heat exchanger. (You can probably understand why I wonder whether this was valuable technical information or a scary hard sell.) I don't know whether he tested all the safety controls. My guess is that he did, because the company he works for has been in business here for decades, and is one of the biggest HVAC companies in this city. I would expect them to do a good job, even if they were also trying to frighten customers into buying new equipment.

Stan

There is not much need for roll out switches on induced draft equipment as the fan PULLS the gasses thru the unit as opposed to relying on gravity.

This pull or induced as they call it is also why it is very low risk of getting CO from the unit to your living space.

I have a 20 year old 90 plus Heil in my home, check it every year and have no worries.

I do however KNOW that all my safety controls are working correctly since I test them myself.

I also observe NO CHANGE in the flame pattern when the blower starts.

I did pull my primary heat X a couple years back and inspect it just for grins.

While it is all torn down one can inspect and clean the secondary and the A/C coil.

John,PA · Oct 31, 2014

WHITE ASH...........
.
I finally read your thread, completely.

Technician reported "WHITE ASH" on the heat exchanger.

All that means, for Nat. Gas.....time for cleaning. Especially if the "ash" starts plugging up the burner jets.

John,PA

JDemaris · Nov 1, 2014

I guess "they don't built them like they used to." My barn has a Firestone "Air Conditioner" built in 1948. Oil hot-air furnace. Doesn't even have a flame sensor. Uses a stack sensor for safety. Once I had to patch the heat exchanger because of a refractory problem. Been fine ever since. So it's near 80 years old and still runs 75% efficient. Not much different then many new ones.
I paid $50 for it in 1979 when the homeowner was replacing with new. Since then, same homeowner has had three furnaces goe bad.

John,PA · Nov 1, 2014

I like the older equipment, myself.
My hot air furnace (oil fired) is 40+ yrs. old.
The heat exchanger in my YORK furnace is 16 ga.
All the new stuff is just stamped outta tin foil, as far as I am concerned.

I like standing pilots, especially if a furnace sits all summer long in a damp basement. The heat exchangers seem to last forever.

I quit servicing residential heating equipment when they came out with "hot surface ignition" to save gas. Real headackes for stocking parts.

In this area, would you believe, there are still some of those "OCTAPUS" coal furnaces which were converted to nat. gas when the gas line came thru.

It would be hard for me to select a new hot air furnace that didn't have all of the electronic and extra blowers just to same a little gas. What you will save in gas, you will spend replacing furnaces.

JDemaris · Nov 1, 2014

Some of the new furnaces are not that more efficient anyway. I just bought a brand new natural gas furnace for a rental I own. 75% efficient. Yes there were models with higher ratings and also more trouble prone.

My parents house where I grew up still has a converted coal furnace. They are long dead but that furnace keeps working. It was converted to oil back in the 40s. Hot water and radiator system.

John,PA · Nov 1, 2014

STAN,

I am goi'N OFF DUTY. Almost 1200, here.

We we clean a furnace, annually, WE remove the blower assembly, take outside, and blow out the windings, squirrel cage, especially. Very often the FAN MOTOR is the real culprit to make sure it is proper for the appliance. It should be rated FAN DUTY! Sometimes anything will do in an emergency, until the proper motor can be secured. The motor is usually in the return air stream. If it is an "open " motor, dust particles, human and animal DANDER, daily living debris will accumulate.

The motor can over heat and its internal thermostat will cause to click off the motor.

This procedure is ESPECIALLY important for ATTIC-TYPE installations. That is right, a lotta of attic fires. Especially down SOUTH!

GOOD LUCK.

John,PA

M-MAN · Nov 1, 2014

Just replace the 20 year old furnace so you'll have less stress and sleep better.

Catastrophic hx failures resulting in house fires are rare but it is possible. Just for grins assume a three inch piece of metal fell out of your hx. If that happened the burner flames would blow around just like your grill fire when the wind blows. That fire will overheat the thermo-disk roll out switches that are between the burners and anything else that can be harmed and shut down the furnace. Unlike the other single safety devices there are at least two roll out switches. For $20 you could add a set to anything. Should those roll out switches fail the flames could overheat the gas valve and cause it to rupture resulting in a house fire. The busted hx must damage something else before there can be a catastrophic event.

Geo-TH,In · Nov 1, 2014

I replaced the heat exchanger about 30 years ago in a gas furnace with a standing pilot. It was no fun. Had to take about every nut, bolt, and screw lose.

Before I would worry about replacing a 20 year old heat exchanger, just buy a new higher efficiency furnace and have it on hand. Or like I told you before, definitely have a CO and CO2 alarm. This will give you some warning before you a total melt down on a heat exchanger. Many times a hole in heat exchanger causes an issue with blowing air inside where the flame is.

If you are worried, mobile home furnaces have more hi temp limits than the older house furnaces. Just add some hi temp limits switches in series with the other limits.

I have portable back up LP heaters in case I lose electricity, total electric. Get some kind of back up you can use if you need to replace furnace.

ss55 · Nov 1, 2014

Below you posted that your furnace is a high efficiency (90+%) unit. Heat exchangers are much thinner on those to get the higher thermal efficiency. In this area twenty years of life on one of those is past being on borrowed time. You may want to have it inspected by another shop.

I would start setting aside some money for a replacement furnace. In the off-season most shops offer reasonable discounts. If you have to replace it at the the beginning of the season when installers are all busy, you may have to pay full price plus overtime on the installation.

Two more questions about furnace heat exchanger

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