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  1. #14
    Join Date
    Feb 2004
    Posts
    2,462
    I installed a G12 in our house about 25 years ago and still cooking.

  2. #15
    Join Date
    Jul 2005
    Posts
    12
    thanks for all the posts.

    Any reason why spark ignition is no longer use, if it is so reliable (compared to hot surface ignition)?

    My tech mentioned that the York's heat exchanger is still holding up well, and he thinks I should consider its reliability. He warns me that new furnaces are "fragile" (sensitive circuit boards, electronics). Is that really the case?

    As for my neighbor's furnace: Does anyone know when Lennox stopped producing the G12 furnace? My neigbors is trying to ascertain the age of their Lennox G1203 furnace. They are torn between replacing a reliable furnace that have served them well with minimum fuss (not surprising, in a very simple design with stnading pilot), but runs up high gas bills (with rising natural gas prices year after year), or replace with a new 91%+ furnace. they have changed their windows to double pane, and they have gotten insulation added too. Any comments/advice about keeping an old faithful and reliable, but expensive to run furnace vs. getting a new high efficiency one, they would love to hear from folks (techs and homewoners) about their experiences. Thanks.

    Originally posted by mike3
    I installed a G12 in our house about 25 years ago and still cooking.

  3. #16
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,320
    My guess would be cost, on the spark system, to manufacture.

    No more fragile then a new car compare to an old one.
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  4. #17
    Join Date
    Jul 2005
    Posts
    31
    I have a Lennox G11 that is original to my house built in 1979. Even though the heat exchanger is in great shape, I will be upgrading to a new furnace this summer; the furnace is way oversized, and I can't stand the $ 400+ gas bills anymore!

    The previous homeowners had the gas company upgrade the standing pilot to electronic spark ignition, which has been trouble free. Something your neighbor can look into if they want to get rid of the pilot without the expense of a new furnace. FYI-I'm just a homeowner like you; it's just a thought. The professionals here might have a different opinion on the subject, though. Good luck!

  5. #18
    Join Date
    Mar 2004
    Posts
    1,042
    Your operating costs will certainly drop by replacing the old equipment. The current equipment is approaching the age where reliability starts to become of real concern.

    Make sure when you do go to replace the equipment that you get a new load calculation done. Since you've made all those insulation upgrades to the house, it doesn't need as much heat anymore, and a furnace that's too large for the job (new or old) can't run at its rated level of efficiency. Since furnaces are normally rated by their burner (input) size, you'll also need a smaller unit because the new one will put out more heat for a given input. For example, 70% efficiency times 82,000 BTU input equals an output of 57,400. Since we assume the old furnace always did the job, even without the extra insulation and new windows, we can assume that the old heat loss number was less than 57,400. With the insulation upgrades, the actual heat loss may have dropped 10,000. All told the actual heat loss may be something like 40,000 now. With a 93% efficient furnace, you need an input size more like 45,000 to do that job.

    These are all back-of-the-napkin numbers, though, just to illustrate that the new furnace should probably be "smaller" than the old one. Get someone to do a Manual J load calculation when you actually do get the equipment replaced.

  6. #19
    Join Date
    Jul 2005
    Posts
    12
    Thanks for all your comments. My neighbors couldn't agree more about expensive gas bills, and looking to save!

    BTW, I went over to my neighbor's place and took a look at their furnace, and I found out that it is a Lennox G12Q3 (not G1203, as I was informed). So, here's the correct info:

    Lennox G12Q3-82 (S/N: 5878B-13669 (82,000 BTU) with standing pilot.

    Am I right to guess from the S/N, that this furnace dates back from 1978? My neighbors bought their house in the 1990s, and because the house has changed hands several times, the sellers didn't know when the furnace was installed.

    Bottom line they want to know, is it worth tinkering around with a 27-year old furnace, the operating age of a typical heat exchanger in a the G12-series furnace? I searched around Lennox's website, and in their archives, found the manual for the G-12. It says that this series uses a "Duracurve" Heat Exchanger? Anyone knows anything about this "Duracurve" Heat Exchanger?

    Thanks for your help!

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