Page 2 of 3 FirstFirst 123 LastLast
Results 14 to 26 of 37
  1. #14
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,271
    I've found in most cases you can just leave the 2nd stage unhooked completely since furnaces are typically sized twice as big as needed. Set the system as "two stage" and never use stage 2.

  2. #15
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,728
    Quote Originally Posted by BaldLoonie View Post
    If it is a GMH, you can't use a 2 stage stat
    +1

    Not really a 2 stage furnace. Won't be polishing that one...

    Quote Originally Posted by 54regcab View Post
    The fact Goodman makes a 2 stage furnace w/o the capability to be optimized with a 2 stage stage leaves a bad taste in my mouth about Goodman...
    Hmmm. Not sure that's fair.

    Quote Originally Posted by 54regcab View Post
    I've found in most cases you can just leave the 2nd stage unhooked completely since furnaces are typically sized twice as big as needed. Set the system as "two stage" and never use stage 2.
    Sad but too true. Most with multiple stage furnaces spent xtra and got nothing for it. GMH at least is cheaper than a real 2 stage furnace.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  3. #16
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,692
    Quote Originally Posted by 54regcab View Post
    It can also happen during recovery from setback.
    I had not thought of that, but so true.

  4. #17
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,048
    Quote Originally Posted by tedkidd View Post
    +1

    Not really a 2 stage furnace. Won't be polishing that one...



    Hmmm. Not sure that's fair.



    Sad but too true. Most with multiple stage furnaces spent xtra and got nothing for it. GMH at least is cheaper than a real 2 stage furnace.
    It IS a real 2 stage furnace. It has 2 stages.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  5. #18
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,728
    It is a "modified 2 stage" system. Low can run for the first 5 minutes, or 1-12 minutes at the BEGINNING of the cycle. To me, this is a soft starting single stage.

    I guess technically it is a 2 stage, but it misses 90% of the benefit of 2 stage. Any furnace that can't run high first then low, in my view (energy and comfort), misses the point. Ideally a 2 stage can cycle back and forth, modulating in an attempt to match envelope losses.

    (http://site.mypointnow.com/documents/25-k120602.pdf p12. Also, notice it doesn't even list a low output on spec sheet. )

    The real problem comes in when the sales person who like to oversize doesn't understand how this turd operates. He figures he can size to low stage and have "high for fast recovery". Now you have a grossly oversized piece of equipment you can't even lock on low.

    I Audited a house with one of these. 2200 sf, 120,000 btu. Client replaced a 30 year old furnace a year before I got there (same size of course). Bill analysis showed NO ENERGY SAVINGS and they have all kinds of comfort issue.


    IMO, calling it 2 stage is like painting a dog turd gold and calling it a gold brick. Makes true 2 stage devices look bad by association.
    Last edited by tedkidd; 10-12-2012 at 10:49 AM.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  6. #19
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,338
    I can see the timed two stage approach working correctly if:

    a) The high stage is sized for the winter design day (not low stage)

    b) Setback swings are minimized or eliminated

    c) The building envelope is above average in thermal integrity (including duct leakage)

    I would agree with you, Ted, that if the furnace high stage is being sized for "fast recovery", that's foolish. How is "fast recovery" quantified in engineering terms? "Oh, it should warm your house back up from 55 to 72 in about fifteen minutes". Sure, if you have a volcano blazing away inside the box, that might happen.

    The benchmark is the winter design day, not sizing low stage for winter design and then relying on high fire for setback or other recovery demand.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  7. #20
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,728
    What it does is provide a gentle start. It puts some btu to the duct so that when the fan ramps up it's not blowing really cold air at max velocity.

    But imagine my frustration spending hours trying to figure out how to manage staging so I could help improve comfort and energy consumption, and my disappointment when I finally understood what this thing is.

    It's the epitome of "heat UP and shut off" design philosophy.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  8. #21
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,338
    Quote Originally Posted by tedkidd View Post
    What it does is provide a gentle start. It puts some btu to the duct so that when the fan ramps up it's not blowing really cold air at max velocity.

    But imagine my frustration spending hours trying to figure out how to manage staging so I could help improve comfort and energy consumption, and my disappointment when I finally understood what this thing is.

    It's the epitome of "heat UP and shut off" design philosophy.
    If the furnace is sized correctly for the structure, do you still see this control strategy as problematic?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  9. #22
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,728
    As I watch my grossly oversized furnaces quickly satisfy my rental units and shut down even with a 2f deadband, I have a hard time imagining ever recommending single stage appliances. "correctly" sized means it's oversized all but a few hours of a few random days during a season.

    So I'm not a good one to ask.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  10. #23
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,338
    Quote Originally Posted by tedkidd View Post
    As I watch my grossly oversized furnaces quickly satisfy my rental units and shut down even with a 2f deadband, I have a hard time imagining ever recommending single stage appliances. "correctly" sized means it's oversized all but a few hours of a few random days during a season.

    So I'm not a good one to ask.
    The way I see it, residential heat load calculations came of age in a time when single stage equipment, heating or cooling, was the norm. Sizing correctly for that 2% slice of the year does mean the equipment is oversized 98% of the time, provided the equipment can actually deliver the amount of BTUs a "design day" situation calls for. For gas/oil heating this is usually done in spades; for a/c and heat pumps, it can get very close, or even come up short.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  11. #24
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,692
    Quote Originally Posted by tedkidd View Post
    What it does is provide a gentle start. It puts some btu to the duct so that when the fan ramps up it's not blowing really cold air at max velocity.

    But imagine my frustration spending hours trying to figure out how to manage staging so I could help improve comfort and energy consumption, and my disappointment when I finally understood what this thing is.

    It's the epitome of "heat UP and shut off" design philosophy.
    The older Goodman's 90+% (and maybe other brands), without the variable-speed blowers, did not have 2-stage blowers. They blew hard on "low stage". You get what you pay for, generally speaking.

  12. #25
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,048
    Quote Originally Posted by tedkidd View Post
    It is a "modified 2 stage" system. Low can run for the first 5 minutes, or 1-12 minutes at the BEGINNING of the cycle. To me, this is a soft starting single stage.

    I guess technically it is a 2 stage, but it misses 90% of the benefit of 2 stage. Any furnace that can't run high first then low, in my view (energy and comfort), misses the point. Ideally a 2 stage can cycle back and forth, modulating in an attempt to match envelope losses.

    (http://site.mypointnow.com/documents/25-k120602.pdf p12. Also, notice it doesn't even list a low output on spec sheet. )

    The real problem comes in when the sales person who like to oversize doesn't understand how this turd operates. He figures he can size to low stage and have "high for fast recovery". Now you have a grossly oversized piece of equipment you can't even lock on low.

    I Audited a house with one of these. 2200 sf, 120,000 btu. Client replaced a 30 year old furnace a year before I got there (same size of course). Bill analysis showed NO ENERGY SAVINGS and they have all kinds of comfort issue.


    IMO, calling it 2 stage is like painting a dog turd gold and calling it a gold brick. Makes true 2 stage devices look bad by association.
    A dog with3 legs is still a dog. A 2 stage furnace weather it can be controlled by the stat or not is still a 2 stage furnace.

    Although I'm not a fan of the GMH. When sized correctly. And used with a stat that is CPH based. It runs in first stage a majority of the year.

    There's lots of other 2 stage furnaces installed there controlled by the thermostat, but there over sized so they don't get long run times anyway.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  13. #26
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,728
    Quote Originally Posted by beenthere View Post
    Although I'm not a fan of the GMH. When sized correctly. And used with a stat that is CPH based. It runs in first stage a majority of the year.
    CPH. That's a trick I never dug into. Im trying to get my head around it. (ObeewhanBT, how could you not have taught me about this before now!)

    Set board for long first stage? Limit CPH to drive cycle time up? Sort of like setting larger deadband?

    What other fun stuff do you use CPH for?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

Page 2 of 3 FirstFirst 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event