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  1. #14
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    Jun 2001
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    Moore, Oklahoma, United States
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    You're not trading a "little extra", you're basically dumbing it down to a 14-15 SEER unit with a "overdrive". A 2 ton 15 SEER unit will have a similar power bill to a 21 SEER 3 ton unit. Both units have similar EERs @ 95 outside. The extra SEER is mostly gained from reduced cycling losses, which go away when the unit is oversized. You're basically paying twice the $$$ to get the reserve capacity. And you will need 3 ton ductwork instead of 2 ton ductwork.

    I've never seen a installed 2 stage less than 3 tons, most are 4 or 5 tons.

  2. #15
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    Jul 2012
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    Western KY
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    Quote Originally Posted by 54regcab View Post
    You're not trading a "little extra", you're basically dumbing it down to a 14-15 SEER unit with a "overdrive". A 2 ton 15 SEER unit will have a similar power bill to a 21 SEER 3 ton unit. Both units have similar EERs @ 95 outside. The extra SEER is mostly gained from reduced cycling losses, which go away when the unit is oversized. You're basically paying twice the $$$ to get the reserve capacity. And you will need 3 ton ductwork instead of 2 ton ductwork.

    I've never seen a installed 2 stage less than 3 tons, most are 4 or 5 tons.
    OK.

  3. #16
    Join Date
    Jul 2008
    Location
    Rochester NY
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    Nice thread!
    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.

  4. #17
    Join Date
    Nov 2004
    Location
    SW FL
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    6,273
    Quote Originally Posted by 54regcab View Post
    You're not trading a "little extra", you're basically dumbing it down to a 14-15 SEER unit with a "overdrive".
    A 2 ton 15 SEER unit will have a similar power bill to a 21 SEER 3 ton unit.

    I've never seen a installed 2 stage less than 3 tons, most are 4 or 5 tons.
    How many new houses are < 1,600 Sq Feet?
    It's definitely becoming less common.

    How many people [ including mechanical contractor sales personell ] with a more reasonable sized residence actually realize that =_ Smaller A/C = Better_ ?

    When that concept is fully understood and beLIeVED, you may start to see 2 ton 2-stage ( or a larger FULL MODULATING ) units in < 1,600 sq foot residences.

    Of course, in regions with low electric rates + milder summer climates, owners will not be willing to pay the front-end cost without an envi$ioned pay-back.

    With significantly Higher electric rates in the coming 10 to 15 years + climate change, the feeling of _ what is a reasonable front end cost_ may also be modified.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #18
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    Jun 2001
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    Moore, Oklahoma, United States
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    Good points Dan. As people start realizing this I think we'll move towards more minisplits.

  6. #19
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    Jul 2012
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    Western KY
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    That's what I love and hate about this topic. As things change, things change. Some guys like to stay rite up on the lead edge and are always looking for another % efficiency or the next step towards perfection. Other guys resist change and insist if it aint broke quit fixing it. I remember the first shop I worked for years ago believed 400 sqft per ton. Period. Was that wrong? Maybe to some. But for that guy that's what worked. They did hundreds of new homes and seemed to work fine. Some guys like to squeeze every penny, up front and efficiency wise which is great. But there is a trade off. This last summer is a good example. Our resi guys ran hundreds of calls on systems that were simply maxed out and giving up 2-5 degrees in the afternoon. Customers don't understand and don't like to hear "it's doing all it can". They love the savings from the efficiency but loose a big chunk of it on the tech coming out going through the system and explaining it to them. Perhaps better explaining to customers up front and the option given to them would help. I think 550 sqft per ton is a safe range myself. Is efficiency lost at that range? Perhaps. But 650-700sqft per ton is comfort sacrificed? Perhaps. It depends on the customer and what their opinion about priority is. I love and hate this topic!! We are all wrong and all rite. Now let the screaming begin.

  7. #20
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    Rochester NY
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    Quote Originally Posted by Tommy knocker View Post
    Our resi guys ran hundreds of calls on systems that were simply maxed out and giving up 2-5 degrees in the afternoon. Customers don't understand and don't like to hear "it's doing all it can". I think 550 sqft per ton is a safe range myself. Is efficiency lost at that range? Perhaps. But 650-700sqft per ton is comfort sacrificed? Perhaps. It depends on the customer and what their opinion about priority is. I love and hate this topic!! We are all wrong and all rite. Now let the screaming begin.
    Good post. But ya need to stop taking responsibility for crappy enclosures.

    That's a no win for you. Fixing every comfort problem with equipment is a slippery ethical slope, and communicating to homeowners that work on the enclosure is an opportunity needs to be part of the hvac guy's pitch.

    You wouldn't give a loaded gun to your teenager without a fair amount of training or you'd carry responsibility for the ensuing accident. Sizing to what you can expect a home can reasonably be expected to be improved to, or at least expressing that you feel this is best policy when discussing design with ho, is ethical responsibility. Ignorance of this opportunity can no longer be claimed. "Shouldn't the HVAC guy have told me?" now is met with "yes."

    You install 550 per ton you have an obviously deficient house. Likelihood is high the homeowner will decide air sealing the house is a good idea in the near future. Press and incentive programs for weatherization are ever more prevalent, so if you neglected to explain this, resultant humidity, short cycling, and temperature imbalance are certainly getting laid at your feet.

    And if it's not clearly documented that you indicated the house has gaping deficiencies, that the ho asked you to size to although you recommended against, your feet is where responsibility belongs. Do everything you can to limit theat exposure. The hvac co coming in behind you, under auspices of comprehensive assessment, will crucify you and your work if you aren't cautious here. "Boy that guy did you a disservice! Your comfort issues are due to leakage AND oversized equipment. As we fix leakage your over size problem gets WORSE!" Once companies find themselves installing smaller equipment for free, this point will begin to become apparent.

    Educate that all problems are not effectively solved with equipment, and when they call on that super hot day you can remind and ask if recommended weatherization work was completed. If they haven't and don't want to do that, suggest a window unit or mini. (You can educate ignorance but ya can't fix stupid. The first is a reasonable expectation, I don't think any reasonable person expects the second.) Doing your best to leave future options for improvement open to your HO's, that does seem a reasonable expectation for a trusted professional.
    Last edited by tedkidd; 10-05-2012 at 10:55 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.

  8. #21
    2.5 ton unit sounds like a decent compromise to me. IMO

  9. #22
    Join Date
    Aug 2009
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    Jurupa Valley, CA
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    1,777
    The other advantage of the 2 / 3 ton 2-stage unit is that since the coils are sized for the three ton, the efficiency of the 2ton mode is increased (the "oversized" coils improve heat transfer capability)... Since it will bee running at 2 ton most the time, it may even use less energy than a plain 2 ton unit.

  10. #23
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    Jun 2001
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    Moore, Oklahoma, United States
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    Quote Originally Posted by CraziFuzzy View Post
    The other advantage of the 2 / 3 ton 2-stage unit is that since the coils are sized for the three ton, the efficiency of the 2ton mode is increased (the "oversized" coils improve heat transfer capability)... Since it will bee running at 2 ton most the time, it may even use less energy than a plain 2 ton unit.
    Oversized coils happen when you move from 13 to 14\15 SEER single stage. Increasing coil size beyond that of the 15 SEER unit has minimal impact on EER.

  11. #24
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    Jan 2009
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    Keokuk, IA
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    Quote Originally Posted by CraziFuzzy View Post
    The other advantage of the 2 / 3 ton 2-stage unit is that since the coils are sized for the three ton, the efficiency of the 2ton mode is increased (the "oversized" coils improve heat transfer capability)... Since it will bee running at 2 ton most the time, it may even use less energy than a plain 2 ton unit.
    The only problem is that if you're talking an unloading scroll, a 3 ton unit will be clsoer to 2.3 ton on low stage. So now you back ot being oversized and short cycling.... and worse, now you have a really big coil in low stage that will struggle to dehumidify. SO yes, very efficient in terms of total BTU's. Not as ideal for comfort.

    I owned a 3 ton 2 stage on a home that needed 2 tons. Not a good set-up. I saw higher elec. bills going from a 9 SEER to a 15 SEER since it short cycled so much and didn't dehumidify well. IT was made even worse because it got matched with a 4 ton coil... and even worse a XL16i which are well known ot have poor latent capacity on low stage. I learned that lesson that hard way.

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