Replace heat exchanger or entire furnace?

Discussion in 'HVAC' started by lou-in-usa, Mar 14, 2018.

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  1. Mar 14, 2018 #1

    lou-in-usa

    lou-in-usa

    lou-in-usa

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    I have a lowboy oil furnace circa 1996, I've serviced it fairly regularly, although last year the igniter worked intermittently and I think saturating the mineral insulator with fuel oil several times and lighting it up, was more than that part could take. In cleaning the blower squirrel cage I discovered the hole in the heat exchanger. The distributor is checking with the furnace manufacturer tomorrow, but he said if they still have the part, it'll be $550. I got a price on a new furnace of $4400 installed. Considering that the efficiency of the new furnace is no higher than this one, and my burner was just tuned-up, and my blower is freshly cleaned, what reason, other than a newer cabinet, would I replace this furnace?

    Now, the tech told me changing the heat exchanger is a pain in the neck job, and would rather do a new install, but how bad could it be?
     
  2. Mar 14, 2018 #2

    nealtw

    nealtw

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    Does the 550 include labour?
     
  3. Mar 14, 2018 #3

    lou-in-usa

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    No, that is part only. Hiring out the labor would be optional for me, I'm comfortable doing it myself. One thing I know is that part of the$4400 price quote is for the possible need to reshape the collars on the duct-work since the new furnace dimensions are likely going to be slightly different. I'd rather not have to have that done. I consider the furnace a sheet-metal box that holds three components: a burner, a fan, and the heat-exchanger; and the "box", fan and burner are in great shape.
     
  4. Mar 14, 2018 #4

    nealtw

    nealtw

    nealtw

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    So you can keep your cost down and be as good as new. The only other thing I can think of, at some point does the insurance company ask how old it is.:rolleyes:
     
  5. Mar 14, 2018 #5

    lou-in-usa

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    Ok, I just ordered the part. The distributor is having it drop shipped to me...3-5 days they said. I'll post my experience.
     
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  6. Mar 15, 2018 #6

    slownsteady

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    I'm glad you made a decision, and I don't really want you to second guess yourself, but how did you come to the conclusion that a 22 year old furnace is the same efficiency as a new one? How much would a higher-tech one have added to the bill?
     
  7. Mar 17, 2018 #7

    lou-in-usa

    lou-in-usa

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    I'm glad you asked slownsteady; just looking at the AFUE numbers for the new unit confirms that, but on top of that, even if the new furnace were 5% more efficient, the question is, how many years would it take to recover the $3900 more spent on a new furnace? If I buy $2000 of oil per season and say with the new furnace, I spend 5% less, or $100, that's 39 years! I call the reasoning, the "Cash for Clunkers-buy a new Prius" logic; in other words, spend a lot of money, to save a little money.

    The other thing is, in speaking with the HVAC contractor about the new unit, there was nothing in what he told me, that led me to believe that my interpretation, that a furnace is just a sheet-metal box that holds a fan, burner & heat-exchanger, is any different than just that...and two out of three of those parts in my old furnace are working just fine. He said a variable speed fan would be extra, so would a burner that can vary output.

    Finally, while forced hot air would be my last choice for a heating system, I had no choice when we bought the house, and I'm not going to retrofit just so I can feel better about my heating system.
    I hope that explains my reasons well enough!
    -Lou
     
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  8. Mar 17, 2018 #8

    lou-in-usa

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    I got the old heat exchanger out this morning, it took a little more than 2 hours, for the most part because I started taking apart the burner side more than I had to. The exchanger was easily removed from the opposite side (rear of the furnace), and this gives me the ability to thoroughly vacuum and clean the inside of the cabinet and the A coil. I have to say this was a lot easier than I expected, and if I weren't organizing and performing the disassembly so carefully, and I knew which end to start from, it would have been out in an hour. So much for "it's a pain in the neck job"; it seems a whole lot easier than replacing the whole furnace. Well I'm going to take the opportunity to buy a new utility steam cleaner that my wife said she'd like to have, and use it to clean the A coil. I'm sure the contractor wouldn't have bothered with that. Anyway, I'll post some pictures later.
     
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  9. Mar 21, 2018 #9

    lou-in-usa

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    Okay, I got the furnace running. I got the heat-exchanger yesterday and decided to get working on it last night. The welding quality on the new one doesn't appear to be as good as the old one, 20180320_141152.jpg but it doesn't have a hole in it...and who knows, at 22 years old, this may have just been a "spare parts" quality weld job at the end of the mass production run. Anyway, I had designs on modifying the humidifier and blower, but the parts are not here yet. So the only upgrade I did so far is a UV light. I thoroughly cleaned the plenum and A coil; everything thing smells pretty good considering some residual oil must be burning off the heat-exchanger. One thing I addressed was the 3/8" gap between the condensation tray and the sheet metal. 20180320_200602.jpg I cut and folded the sheet metal up to conform with the curves of the tray, and then used some flashing tape to hold it. You can see the empty cabinet in another picture, nothing scary about your furnace....it's just a sheet metal box! 20180320_200634.jpg
     

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  10. Nov 7, 2019 #10

    lou-in-usa

    lou-in-usa

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    An update:
    During the 2018-2019 winter, my Beckett oil burner was tripping out, and in the past it would happen here and there, but this time I couldn't get the burner to fire up no matter how many times I pressed the reset button. So I took the burner out of the furnace, purchased a new pump screen & gasket kit, replaced the nozzle, cleaned the electrodes and set the gap, and even all that didn't make it fire for more than a few seconds. Finally I put a pressure gauge on the pump and saw the oil pressure fluctuating wildly, so I figured it had to be the pump, and so I replaced that, and STILL the problem wasn't solved. After fiddling with that for way too long, I noticed that even though the pump shaft had a flat on one side, making the end of the shaft look like a 'D', in the several times I had put the pump back on the burner, I never had to align the pump and motor shaft. Well it turned out that the pump and motor aren't connected directly, there is an intermediate PLASTIC shaft coupling, about 4" long, that connects the two shafts, and the 'D' hole on the plastic coupler, was ROUNDED OUT!

    Anyway, now it all makes sense... This shaft coupler had been starting to fail over the past couple of years, and I suspect that the heat exchanger fiber lining got saturated with oil, because the coupling would skip, which would lower the oil pressure enough to make the burner flame go out, and then the pump would catch here and there, as the burner would try to re-ignite, but spraying liquid oil all over the fiber insulator of the heat exchanger in the meantime. And on occasion, re-ignition would take too long, the burner would just trip out.
    So the message is to check and replace this $7 plastic coupler that can cause so many problems when it starts to fail.

    Since replacing that part, I've decided to keep an extra one on hand, but otherwise the furnace has been working perfectly.
     
    Last edited: Nov 7, 2019
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  11. Nov 7, 2019 #11

    bud16415

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    :thankyou: It is always great to get the rest of the story.
     

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