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  1. #27
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    My god.

  2. #28
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    Dec 2007
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    This guy is saying pay attention to the entire combustion air zone.

    The guy never said that a cracked heat exchanger should not be replaced.

    He said there's no reason to force a family into the cold and shut down their forced-air furnace just because you found a small crack or hole in a heat exchanger. If the flame is not rolling out, or there is some other un-safe condition, then red-tag it, check it for CO output (which it probably won't have) and note on the service ticket that the owner needs to replace the heat exchanger or furnace.

    Then check the rest of the job. Make sure there is adequate flow up the flue, that combustion air is sufficient and that the occupant isn't running an attic fan or other big exhaust fan (kitchen hood) that could back-draft the flue. Recommend that they change the battery in their CO detector, and if they don't have one, get one. Sell them one.

    Every CO incident (and fatality) I've looked at has been caused by problems external to the furnace. Usually it is a blocked flue, sometimes it is blocked combustion air vents/ducts or inadequate combustion air supply, sometimes it is negative pressure around the furnace caused by leaking return-air ducts.

    A forced-air furnace with an air-conditioning coil on it produces enough static pressure inside the furnace cabinet that there is NO way burned gasses from inside the heat exchanger can transfer to the indoor air stream. It is physically impossible.

    The blower will push air into the crack or hole in a heat exchanger in every case. This holds true for furnaces with atmospheric burners and draft inducers. The blower air pressure is what causes the flame to waiver or roll out the front of the furnace. So, even if the CO output from the burners was "high", it goes up the flue or out the front of the furnace. It never makes it into the indoor air stream.

    Go back and re-read the information on the web site. Note that this circumstance only applies to residential non-condensing furnaces, NOT roof-top units, unit heaters, boilers, etc.

    Condensing furnaces with secondary heat exchangers seem to create some kind of turbulence that can cause CO to show up in the furnace cabinet when the secondary is partially blocked and is leaking because of cracks.

    The whole point is to check the entire job, not just the equipment.

    Reaching around to pat yourself on the back for finding a little crack and "saving the homeowner" is a little premature if you haven't thoroughly checked the flue, combustion air, return-air and any other external circumstance that could affect the flue or furnace operation.

  3. #29
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    Dec 2005
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    Cincinnati, Oh
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    Quote Originally Posted by Gus_Scorchio View Post
    This guy is saying pay attention to the entire combustion air zone.

    The guy never said that a cracked heat exchanger should not be replaced.

    He said there's no reason to force a family into the cold and shut down their forced-air furnace just because you found a small crack or hole in a heat exchanger. If the flame is not rolling out, or there is some other un-safe condition, then red-tag it, check it for CO output (which it probably won't have) and note on the service ticket that the owner needs to replace the heat exchanger or furnace.

    Then check the rest of the job. Make sure there is adequate flow up the flue, that combustion air is sufficient and that the occupant isn't running an attic fan or other big exhaust fan (kitchen hood) that could back-draft the flue. Recommend that they change the battery in their CO detector, and if they don't have one, get one. Sell them one.

    Every CO incident (and fatality) I've looked at has been caused by problems external to the furnace. Usually it is a blocked flue, sometimes it is blocked combustion air vents/ducts or inadequate combustion air supply, sometimes it is negative pressure around the furnace caused by leaking return-air ducts.

    A forced-air furnace with an air-conditioning coil on it produces enough static pressure inside the furnace cabinet that there is NO way burned gasses from inside the heat exchanger can transfer to the indoor air stream. It is physically impossible.

    The blower will push air into the crack or hole in a heat exchanger in every case. This holds true for furnaces with atmospheric burners and draft inducers. The blower air pressure is what causes the flame to waiver or roll out the front of the furnace. So, even if the CO output from the burners was "high", it goes up the flue or out the front of the furnace. It never makes it into the indoor air stream.

    Go back and re-read the information on the web site. Note that this circumstance only applies to residential non-condensing furnaces, NOT roof-top units, unit heaters, boilers, etc.

    Condensing furnaces with secondary heat exchangers seem to create some kind of turbulence that can cause CO to show up in the furnace cabinet when the secondary is partially blocked and is leaking because of cracks.

    The whole point is to check the entire job, not just the equipment.

    Reaching around to pat yourself on the back for finding a little crack and "saving the homeowner" is a little premature if you haven't thoroughly checked the flue, combustion air, return-air and any other external circumstance that could affect the flue or furnace operation.
    So to be clear:
    A crack in a heat exchanger should be fixed/replaced/whatever. Just taken care of, but leave the furnace running?

    Talk about a liability nightmare.
    Sure, at the time you check the crack, there may not be a danger.
    God knows what happen after you leave. Heat exchanger gets hot, crack grows.
    You leave the furnace running, and someone dies/gets sick, then you'll be closing up shop.
    That's alot of liability for a company to take, just so someone has heat for a night or 2.

    If you want to take that risk, then by all means go for it.
    Until POLICY changes on what I can or cannot be sued for, Red-tagging will, and should continue.

    Using carbon monoxide detectors to see if your being poisoned doesn't work.
    They're set to high, and poisoning will occur long before they go off.

    so again, "residential non-condensing furnaces" does include forced draft furnaces, which have a positive pressure heat exchanger. Are you saying these wouldn't leak CO, even in the circumstances you propose?

    "The blower will push air into the crack or hole in a heat exchanger in every case. This holds true for furnaces with atmospheric burners and draft inducers. The blower air pressure is what causes the flame to waiver or roll out the front of the furnace. So, even if the CO output from the burners was "high", it goes up the flue or out the front of the furnace. It never makes it into the indoor air stream."

    Out of front of the furnace is normally in the home bud.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  4. #30
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    Dec 2008
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    Looking at your profile Gus. You are not even a tech. Have you ever diagnosed a bad heat exchanger?


    The world is full of sheep, try not to join the flock.
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  5. #31
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    Good info on the subject some of it mentioned here

    http://www.achrnews.com/articles/red...is-responsible

  6. #32
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    Oct 2010
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    Anderson, South Carolina, United States
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    Our company policy is to shut off gas and power if we find a crack, period. I have let them go if they're small on an induced draft, it's really cold, and there are elderly living there. Then we go install a new furnace the next day.

  7. #33
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    Dec 2007
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    [QUOTE=qwerty hvac;16984091]Looking at your profile Gus. You are not even a tech. Have you ever diagnosed a bad heat exchanger?


    That's what keeps me off boards like this ... people who "ass-ume".

    I had some smart-guy tech say that to me ("you're no tech") a few years ago when I was standing with a friend of mine in a basement, trying to explain why he wasn't getting much air flow from a heat run. The tech put out a lot of "attitude" and wouldn't cut me much slack. I was standing with the builder friend and had on slacks and a Polo shirt, so I looked like a normal guy, not grubby like I'd just crawled from under the house. The guy didn't ask who I was, didn't really want to answer any questions and was clearly perturbed that I was there.

    Long story short, the guy doesn't work for that hvac outfit any more. The builder bought the outfit (the shop, trucks and the few regular customers they had.) That guy was first to go.

    I'm here because someone doesn't know their craft and "disparaged" my web site and said it was bogus. On top of not knowing airflow through a residential furnace, folks seem to have a problem reading and understanding.

    Just to put your mind at ease, I've been in the hvac business since 1976. Actually before that if you count clean & and checks during high school. I've been an owner, sales manager, foreman, estimator, technician and manufacturer's rep. When I started, the industry was just "discovering" spark ignition for gas furnaces and were selling upgrade and retrofit packages for existing furnaces to eliminate the standing pilot. That's way before NATE was even a thought. RSES and ACCA and ASHRAE had all the good information and influence. My EPA card is stamped "Universal" and is dated 5/12/1994. What's the date on yours? I've got handtools and test meters (Simpson 260) older than many of you, so before you get all techy, yes I'm familiar with gas furnaces, control packages, ignition systems, heat-pumps, geothermal and zoning systems.

    I guess my question would be why would "common knowledge" be questioned? What, you have to know someone's pedigree to understand when someone tells you that when you throw something in the air, gravity pulls it back to earth?

    A residential gas furnace with an a-coil on the discharge and the blower running is a pressurized box. Inside the box is a heat exchanger. No matter where the hole or crack is in the HX, no matter how big, and no matter how much CO the furnace produces, NONE of the CO is going from inside the heat exchanger to the indoor air stream. It is physically impossible - unless you plan to change the laws of physics. There's a hundred times more air pressure on the outside of the heat exchanger shell than there is on the inside.

    I don't know what fancy classes you guys are taking, or who has been putting this line of BS out for all these years, but it's amazing. It made sense when gravity furnaces existed. It also made sense when those furnaces were converted to in-shot power burners. A split in a heat exchanger would allow coal dust and CO into a house. But that hasn't been true since the advent of the furnace with an integral blower and air-conditioning coil mounted on it.

    The manufacturers love it, however, because it increases their sales. In fact, they count on it. Their engineers pat themselves on the back for helping the company's bottom line.

    You don't have to believe me - try it for yourself. Take an old furnace (atmospheric burner or induced draft, it doesn't matter), put an a-coil on it, drill some holes in the heat exchanger, and drop a purple smoke bomb in the HX. Or use freon and a leak detector, or salt-water and a halide torch, or powdered smoke. As long as the furnace blower is running and the a-coil is in position, you'll never get anything to pass from the HX to the indoor air stream. The blower will always push air into the heat exchanger. (This is NOT true for 90% furnaces with secondary heat exchangers, boilers and packaged units.)

    My problem with the whole topic is that some technicians worry about finding a tiny heat exchanger crack and overlook the flue and combustion air parameters altogether. Fewer people have died because of cracked heat exchangers in modern gas furnaces than those who have perished over the years because of blocked flues.

    Those problems have become synonymous in the news, but they are totally different circumstances. A small heat exchanger crack won't do anything, is hard to even find, and may cause minor changes in combustion analyzer readings. A partially or fully blocked flue, however, may kill the occupants. Unfortunately the media can't tell the difference.

    As far as whether to red-tag and disconnect the furnace, well that depends on how deep your pockets are and what you don't know. First, there's NO directive in most building codes that tells you to dismantle the customer's equipment. It usually says identify the equipment problem, turn it off if it is unsafe and notify the owner and/or occupant. In some municipalities you are technically breaking the law if you disconnect a customer's furnace against their will. That is considered "willful damage" and subject to prosecution. This is obviously an issue when you "red tag" a furnace because of a heat exchanger and the owner has conflicting information from another contractor.

    I'm here to tell you that you need to pay as much attention to the flue and combustion air issues as you do to tracking down and condemning little holes and cracks. You'll save more customers.

    And, just because someone doesn't advertise their pedigree in the who's-who department, doesn't mean they don't have one. Remember, the next unfamiliar nerd that you talk to might be your boss's boss, a majority stockholder, or potential investor. It pays to be polite.

  8. #34
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    Dec 2007
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    Before all you rookies go wonko, here's some basic info from ACHRNEWS.com. This is dated 11/20/2001, so I guess lots of folks forgot to read it.

    Now if you understand that the outside of the heat exchanger is pressurized by the blower .... presto the CO Myth explained.

    This is worth your time to read. http://www.achrnews.com/articles/flu...-installations


    From the bottom of the article:
    Leonard is president of Total Tech HVACR Training, Phoenix, AZ. His firm specializes in service, installation, and application training for service technicians. He can be reached at 602-943-2517.

    Sidebar: CO Article Correction
    Information was added to the CO article [“Hidden Problems Can Cause Carbon Monoxide,” October 10, page 10] that needs to be clarified. Cracked heat exchangers don’t cause CO. This is a common misunderstanding in our industry. Cracked heat exchangers cause one of two problems:

    1. Pushing more air into the combustion chamber; or

    2. Pulling more air into and through the combustion chamber.

    Although both of these situations, for other reasons, are a hazard, in either case, the amount of secondary air is increased, which leans the flame out and reduces CO.

    Publication date: 11/26/2001

  9. #35
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    Dec 2007
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    Here's an article from October 2001 on how to check the entire duct system and house with gas appliances and natural draft flues.

    http://www.achrnews.com/articles/86455


    Wanna know a quick way to kill customers?

    Leave the return ducts open and unsealed or the return headers loose near the furnace during a cold winter.
    You'll be guaranteed to get a few.

    I know, I know ... it's a little dramatic. I've been beating this horse for 10 years: pay more attention to flues and combustion air.

    You're not doing the job if you find a little heat exchanger crack but don't notice that the return trunk has dropped an inch and is separated from the return air panning. The crack won't do anything, but on a cold night, the open return can kill the occupants if it back drafts the flue all night.

  10. #36
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    Quote Originally Posted by hvacvegas View Post
    So to be clear:
    A crack in a heat exchanger should be fixed/replaced/whatever. Just taken care of, but leave the furnace running?

    Talk about a liability nightmare.
    Sure, at the time you check the crack, there may not be a danger.
    God knows what happen after you leave. Heat exchanger gets hot, crack grows.
    You leave the furnace running, and someone dies/gets sick, then you'll be closing up shop.
    That's alot of liability for a company to take, just so someone has heat for a night or 2.

    If you want to take that risk, then by all means go for it.
    Until POLICY changes on what I can or cannot be sued for, Red-tagging will, and should continue.

    Using carbon monoxide detectors to see if your being poisoned doesn't work.
    They're set to high, and poisoning will occur long before they go off.

    so again, "residential non-condensing furnaces" does include forced draft furnaces, which have a positive pressure heat exchanger. Are you saying these wouldn't leak CO, even in the circumstances you propose?

    "The blower will push air into the crack or hole in a heat exchanger in every case. This holds true for furnaces with atmospheric burners and draft inducers. The blower air pressure is what causes the flame to waiver or roll out the front of the furnace. So, even if the CO output from the burners was "high", it goes up the flue or out the front of the furnace. It never makes it into the indoor air stream."

    Out of front of the furnace is normally in the home bud.

    I was going to let this comment slide, but I just can't.


    A crack in a heat exchanger should be fixed/replaced/whatever. Just taken care of, but leave the furnace running?

    Talk about a liability nightmare.
    Sure, at the time you check the crack, there may not be a danger.
    God knows what happen after you leave. Heat exchanger gets hot, crack grows.
    You leave the furnace running, and someone dies/gets sick, then you'll be closing up shop.
    That's alot of liability for a company to take, just so someone has heat for a night or 2.


    If you think that's what will kill your customers, you've got more problems than just perceived liability issues.
    Do you think your liability is any less when you don't find a heat exchanger crack and you tell the customer that the equipment is fine?

    What do you think will happen if the homeowner's husband has a heart attack and dies while she's been baking Christmas cookies and cakes all day and night and it is zero degrees outside and she's kept all the windows closed? The first thing EMS will do is have the fire department check for CO. Since you were the last outfit there, guess what, you'll be in court. The fire department will record a 200 to 800 PPM CO reading. They may, or may not ask the homeowner if she had any gas appliances running. But the report states "complications from potential CO poisoning" and you'll have a lot of explaining to do. So the liability thing is a red herring. It helps sell test equipment and books. Your liability started when you stepped foot on the premises. It ends when you die. They'll reach back 10 years if the lawyers think you have money and they can tie you to the CO incident.

    As far as heat exchanger cracks - you can cut the entire top off a heat exchanger cell and the worst you'll get is a rollout trip and burnt wiring. You can drill holes in the heat exchanger and it won't create a deadly situation. These little cracks everyone is so excited about is a joke. There are hundreds of thousands of gas furnaces that have been running for years with those little cracks. No one noticed.

    Some manufacturer (who shall remain nameless) estimated at a sales meeting that the replacement market for gas furnaces was in the mid 400,000 range back in 2006. I asked one of their engineers how they came up with that number. He said it was based on their estimate that 18% of their furnaces had cracked heat exchangers for units installed in the prior 10 year period. So if heat exchanger cracks were an actual problem, we would have at least a few thousand people dropping dead from CO poisoning in the past few years.

    According to CPSC records between 1990 and 2004 the US averaged less than 124 fatalities per year attributed to gas fired furnaces. That's NOT heat exchanger cracks, that's block and disconnected flues, no combustion air and unidentified reasons.


    so again, "residential non-condensing furnaces" does include forced draft furnaces, which have a positive pressure heat exchanger. Are you saying these wouldn't leak CO, even in the circumstances you propose?


    If you are talking about a residential gas furnace, then the forced draft blower is anywhere from 1/30 to 1/8 HP, I'm guessing? What internal pressure do you think would be developed? Two times atmospheric, three times maybe? I'm going out on a limb here and thinking it might get to .5"WC? I'm totally guessing because I've never measured it. What do you suppose a 1/3HP blower on a 75,000 btuh furnace develops? Depending on the duct work static pressure it can push from .5"WC to 1.5"WC. So, even with a positive pressure heat exchanger, I'm PRETTY SURE that the blower static pressure will overcome total powered-draft static. And, since we're talking about a crack or small hole, the indoor blower will always win.


    Out of front of the furnace is normally in the home bud.


    You got me there, Bud. I'll tell you what, you keep worrying about the little cracks and holes and I'll keep track of my customer's flues and combustion air parameters, and let's track it over the next 10 years. If it goes like the last 10 years, you'll have at least one dead, and I'll have zero.

    But, who's counting?

    Just thought I'd cheer you up.

  11. #37
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    Jul 2010
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    nebraska
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    Never say never Gus. Not too many years ago I got an overtime call about a CO detector going off when the furnace came on. It was an old carrier with induced draft. Long story short there was a crack in a cell which disturbed the flame enough it sooted that cell. When the blower came on massive amounts of CO spilled out of that cell but didn't trip a roll out switch.

    Another the year before was a call because the folks were not feeling well and wanted the furnace checked to make sure it wasn't CO. Walked in to find piles of pet puke all over the floor. Ambient CO levels nearly 100ppm. Source was a natural draft furnace. Rust hole in exchanger which let the cell pressurize when the blower came on.

    No heat call on a Lennox pulse. First thing I always do is pressure test the exchanger, lost it fast as I could put it in. When the guys remove the furnace for replacement the side against a block wall has a 12" spot charred black. Guarantee that one was going into the house.

    Induced GMP furnace with split rings, no AC. Heat exchanger looked good but as it heated up those rings split causing roll out. Again the safeties did not trip.

    I agree with most of what you said. The exception being that CO can not spill into the house through a crack/hole. It's rare but does happen.

  12. #38
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    Jun 2013
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    looked like the new young owners' HX pulled finally after just SMELLING exhaust in their restaurant! and shutting off TWICE they turned on, red tagged... for two weeks before repairs... and I threatened turning in to inspectors that second shut off. I think one blog in a reference to Delaware, they showed the tech/co, is STILL LIABLE in all kinds of angles of user abuse, -but still can cause a dealer/tech to be in question--- if known aware of any such things.
    Process cooling: NO COMPRESSORS Earth-Coupled since 1996
    ... however, much still needs to be hybridized energy transfer.

    CLOSED LOOP 2015 listed EER's
    even 49+ now; and "blended from low to high variable speeds" for 32deg.F ~ E-Star

    Perhaps you need a 32F Chiller/HW-Heat: buy a GEO-T Heat Pump (GHP with Heat-Recovery)
    http://www.energystar.gov/index.cfm?...mal_heat_pumps

    http://www.hydro-temp.com/products.html and Bosch/Carrier and AquasystemsInc.com

  13. #39
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    Crack in HX, advise it as hazard, shut down... its insurance friendly CYA.

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