hausdok Posted September 1, 2009 Report Share Posted September 1, 2009 Hi All, Had a situation yesterday where a client shot me an email to tell me that when he'd finally gotten around to getting the 14-year old furnace on the house he bought serviced, as I'd recommended, that "as soon as the technician opened up the furnace he found a crack in the heat exchanger." I drove over there last night thinking that as soon as I took the cover off that unit that there would be a crack visible. There wasn't. I looked and looked but couldn't see a crack. "Where's the crack," I asked the client. "Behind there," he said, pointing to the bakelite plate behind which I'd find the limit switch if I were to open up the unit. "Well, that explains it," I answered, "I'm only doing a visual inspection on these furnaces and I wouldn't have removed that component to look inside. Other than to remove the cover, about the only thing that I ever remove is the heat shield, if there is one, so that I can get a better look into the combustion chambers." Just to see what kind of crack he was talking about, I pulled the switch to look behind it. There, right at the edge of one of those dimples in the exchanger elements, was a crack. Not a wide crack, mind you, but one that I could feel with the tip of my finger and see. the sides of the crack were slightly offset from one another. It seemed odd to me that a service tech would have pulled that - it's almost like the guy knew what he'd find. Thinking about that crack afterward, I had the sneaky suspicion that if anyone stuck the rubber handle of a screwdriver through that opening and jammed it sideways a little bit that they might have been able to cause that crack; but, not seeing any tool marks anywhere I knew I didn't have a prayer in hell of proving that. Wish I'd asked the client if he'd been there when the HVAC guy pulled that switch though. I reassembled the furnace and explained to him that, not excusing the fact that there is a crack, I thought the furnace company might be overstating their case. Then I explained to him what I'd heard from Ellis Pracht, The Heat Exchanger Expert; that allegedly about 95% of all furnaces have cracked heat exchangers, that the HVAC industry knows it, and that folks aren't too concerned with it because, when the system is running and the fan is on, that the exchanger is under positive pressure, and, if the flame is adjusted to a good 10 to 1 combustion ratio that there is practically no CO being produced and that it was unlikely that it would get into the air of the house unless there was a serious flue obstruction. He told me up front that he doesn't intend to replace just the exchanger as recommended by the tech because it costs about half of what a new furnace would costs; so, if he must he'll install a new furnace. I explained that the new furnace was the way to go but if he opted not to do that right away for some reason he should at least get the HVAC guys back in to check the air/fuel ratios on the furnace to ensure it's burning cleanly and install a couple of really sensitive CO detectors. OK, that's what happened, but the question isn't about the recommendation I made to him - which I'm kind of uncomfortable about - or even about the crack - it's about how far any of you go to look inside one of these heat exchangers. Below this switch/sensor there is a narrow metal shield. Even with a one of Jim's long strips of mirror, I doubt that anyone could have seen the sensor or the crack above it; I would have had to use a See Snake or something similar to get up into the area where that switch is, or done what Pracht is always talking about, pull the plenum on top and looks straight down into the unit or pull the air handler blower from underneath, shinny into that return plenum and look up into the furnace with a flashlight. Or I could do what that particular HVAC tech did and pull that limit switch and look through that 1-1/2-inch wide by 2-1/2-inch long hole. Most of that, with the exception of pulling a heat shield off and using mirrors to look up into the heat exchanger is not how I'd been taught to inspect these things and now I'm wondering if a lot of guys pull these sensors. What say you all? ONE TEAM - ONE FIGHT!!! Mike Quote Link to comment Share on other sites More sharing options...
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