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  1. #1
    Join Date
    Nov 2010
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    145

    Question Oversized Goodman GMH95.. Possible to install burner/board from smaller unit?

    Hi Gents,
    I posted earlier about having had a 92k btu gmh95 with 14 seer 3.5T AC installed.... unfortunately without a load calc. Now have done load calc and heat loss load of 61k. It was partly my mistake and my contractor did not call it to my attention. Water under the bridge.

    Before I spend the large $ to install the 70K 4 ton unit, it appears that the major (only?) difference between the 92k unit I have and the 70k is a 4 burner unit instead of the 3 burner unit + control board. Can a (well) qualified professional order up the parts and install them, set up for me? Anyone here in the Atlanta area that can do that?

    I assume that would "void the warranty". Well, I trust that swapping out a board and burner assembly (gas valve?) is would be far less than a complete install and eating some or all of the cost of the oversized unit too... so a reasonable trade off for loss of warranty?

    Is this possible? Crazy? Thanks for your thoughts.

    shovel99 Paul

  2. #2
    Join Date
    Jul 2002
    Location
    Zelienople, Pa
    Posts
    2,965
    Not possible...

    Eat your mistake and move on.
    How tall are you Private???!!!!

  3. #3
    Join Date
    Nov 2010
    Posts
    145
    That would be eat "our" mistake... the "professional" who just replaced what was there... and me, the uninformed consumer who did not know that "load calc" existed. I was being gracious. But thank you for the reply.

  4. #4
    Join Date
    Oct 2010
    Posts
    59
    Is that a two stage furnace? IF it's oversized and two stage then it probably runs in first stage most of the time anyway and only goes to second stage when recovering from a large setback. First stage would be pretty close to you actual requirement on that size furnace. Modifying the furnace isn't going to save you any money in the long term. You're going to use the same amount of energy to heat your house whether you are using a properly sized furnace or an oversized one. It's just a matter of comfort. A properly size furnace will run longer and provide a more even heat distribution than an oversized one. Your house requires the same amount of BTU's regardless. If money is no object and you want the comfort level then I would just change out the whole furnace for a properly sized one instead of trying to modify your existing one. Just my 2 cents.

  5. #5
    Join Date
    Oct 2005
    Location
    Pacific Northwest
    Posts
    2,266
    Are you having issues other than what the manual J specified?

  6. #6
    Join Date
    Nov 2010
    Posts
    145
    Quote Originally Posted by kb3ca View Post
    Is that a two stage furnace? IF it's oversized and two stage then it probably runs in first stage most of the time anyway and only goes to second stage when recovering from a large setback. First stage would be pretty close to you actual requirement on that size furnace. Modifying the furnace isn't going to save you any money in the long term. You're going to use the same amount of energy to heat your house whether you are using a properly sized furnace or an oversized one. It's just a matter of comfort. A properly size furnace will run longer and provide a more even heat distribution than an oversized one. Your house requires the same amount of BTU's regardless. If money is no object and you want the comfort level then I would just change out the whole furnace for a properly sized one instead of trying to modify your existing one. Just my 2 cents.
    Thanks for your input. You are right on... and it is about comfort, and we may just live with it. With our marginally sized duct system...we are running at the limit of temp rise (126 degrees and 61 degree rise) we get a blast of hot air both temp and volume . At design limits, inadvisable to even drop the Hi heat speed (factory Med Hi) back a notch. I will try lower speed on 1st stage heat,k but my contractor is unresponsive, with health issues. I am confident that the 3.5T air is sized properly.... just stuck here with a blowtorch furnace that is continuous hot and cold spots. If I swap, I will likely get the variable speed, which will at least return some electricity cost with more comfort. We plan to be here a long time.

    shovel99/Paul
    Last edited by shovel99; 01-10-2011 at 11:12 AM. Reason: clarity

  7. #7
    Join Date
    Oct 2005
    Location
    Pacific Northwest
    Posts
    2,266
    Quote Originally Posted by shovel99 View Post
    Thanks for your input. You are right on... and it is about comfort, and we may just live with it. With our marginally sized duct system...we are running at the limit of temp rise (126 degrees and 61 degree rise) we get a blast of hot air both temp and volume . At design limits, inadvisable to even drop the Hi heat speed (factory Med Hi) back a notch. I will try lower speed on 1st stage heat,k but my contractor is unresponsive, with health issues. I am confident that the 3.5T air is sized properly.... just stuck here with a blowtorch furnace that is continuous hot and cold spots. If I swap, I will likely get the variable speed, which will at least return some electricity cost with more comfort. We plan to be here a long time.

    shovel99/Paul

    This must be Robo's shadow posting to tweak AM (inside joke)

  8. #8
    Join Date
    Nov 2010
    Posts
    145

    Smile

    Quote Originally Posted by crmont View Post
    Are you having issues other than what the manual J specified?
    Not that are fixable. Duct work is marginal at best... 60 year old house that has been expanded... added some ducting and returns.. but rooms furthest from systems are "limping" but ductwork is enclosed and expensive to impossible to improve.

    I just read here on HVAC talk that basement returns should be avoided. In 1995 when our last system was installed and half of basement was finished, we added supplies in three rooms comprising 800 SF (below grade)... and a single 10 inch return in a small hallway with two doors which open into unfinished basement... on either side of our furnace/AC unit, which sits next to a gas hot water heater. The return grate is literally 6 inches from the back of the furnace, and there are two cheesy interior doors with gaps under them.. one on each side.. within 18 inches. No makeup air is supplied from outside for either the 92k furnace or 40 Gal Water Heater.

    At full stage, before closing off that return for safety reasons, the supply heat from both stages drives 126 degrees at the register of shortest supply, a run of about 7 feet. I trust this is fairly close to "maximum rise" and was a 61 degree rise at the time. From what I understand, if I choose a slower speed (Say 2nd lowest speed vs the 2nd highest now) ... to reduce the "blower blast"... the temp rise will be higher.... above spec for the unit.

    Other than that, we are fine. Or as they say, "Mrs. Lincoln, How did you like the play?"..

    Don't know what you mean by Roboposting. Not me. Annoyed nut, at this point, maybe, but not a roboposter.

    Paul
    Last edited by shovel99; 01-10-2011 at 01:22 PM. Reason: clarity

  9. #9
    Join Date
    Oct 2010
    Posts
    59
    On my two stage furnace changing the blower speed affects both stages and since you are near the maximum temperature rise I would not recommend lowering it.
    It may be possible to program your thermostat to delay staging or possibly to disconnect the wiring for second stage altogether and run in first stage only since first stage is close to your heat load. Maybe some of the other guys can weigh in regarding the feasibility of disconnecting second stage. Not a professional, just some thoughts I had.

  10. #10
    Join Date
    Jul 2002
    Location
    Zelienople, Pa
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    2,965
    It sounds like you went cheap and got what you paid for.

    Company that didn't do a Man J. and Gooman equipment to boot!
    How tall are you Private???!!!!

  11. #11
    Join Date
    Jul 2005
    Posts
    5,571
    Quote Originally Posted by kb3ca View Post
    On my two stage furnace changing the blower speed affects both stages and since you are near the maximum temperature rise I would not recommend lowering it.
    It may be possible to program your thermostat to delay staging or possibly to disconnect the wiring for second stage altogether and run in first stage only since first stage is close to your heat load. Maybe some of the other guys can weigh in regarding the feasibility of disconnecting second stage. Not a professional, just some thoughts I had.
    There are no provisions for that on this particular furnace.

  12. #12
    Join Date
    Nov 2010
    Posts
    145
    Quote Originally Posted by Gunnery Sergeant Hartman View Post
    It sounds like you went cheap and got what you paid for.

    Company that didn't do a Man J. and Gooman equipment to boot!
    Well, I just didnt' know YOU so I could have you flown over to Atlanta to Install a $20,000 Trane system instead.

    My mistake!

  13. #13
    Join Date
    Jul 2002
    Location
    Zelienople, Pa
    Posts
    2,965
    Quote Originally Posted by shovel99 View Post
    Well, I just didnt' know YOU so I could have you flown over to Atlanta to Install a $20,000 Trane system instead.

    My mistake!
    You're not allowed to discuss prices.

    Please read the site rules...
    How tall are you Private???!!!!

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