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  1. #1
    Join Date
    May 2013
    Posts
    6

    New AC 2-stage confusion HELP!

    I'm new here so I will try hard not to break any rules in posting.

    We have a 1 story 1600 sq ft. house that we are looking to replace the 35 year old furnace and 12+ year old A/C. We are also having the furnace moved from the garage into a more central area in the attic, with the intake being moved into the hall near the furnace.

    We've narrowed it down to a couple of companies that feel comfortable with. But here is our delima, we are trying to choose between an 18 SEER 2-stage unit or a 16 SEER single stage. We live in Southern California near the Mojave Desert, so our weather tends to be hot and very dry in the summer and mild winters. The variable blower furnace is a definate, but I'm just not sure if the $1300+ difference in the 18 SEER is worth it in the long run. We plan on being in the house a long time and don't mind getting the 2-stage if it makes financial sense but don't want to blow money on something that doesn't really pay back dividends. Especially if we could take the $$$ and put it in attic insulation or a couple more dual pane windows.

    Also, it seems that most people who love a 2-stage live in humid climates. I guess the 2 stage helps to run longer and dehumidify the air. Humidity isn't really a problem where we live. Any advice is greatly appreciated.

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,719
    2 stage helps for comfort in humid climates and houses that have temp differences from room to room (longer run times help even out the temps). In a dry climate it won't help too much. The upgrade to 2 stage vs 1 stage will not pay back over the life of the unit. Your money is best spent elsewhere in energy efficiency improvements. Have you or will you be having a home energy audit done to see where you could get the most bang for your buck on energy improvements.

  3. #3
    Join Date
    Oct 2002
    Posts
    1,271
    Single stage is much less problematic. (read- less repairs)

    Never figured into ROI calculations.

    Unlike single stage cooling, seem every manufacture have a different approach to accomplish two stage cooling. Trane uses two compressors, Carrier, reversing compressor and old Lennox, two speed compressor, now unloading compressors are the way. Each have their specific parts and required manufacture training that is confusing.

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,334
    Air distribution is not as good on the low speed fan. In some duct systems, you end up with spots not getting good air flow on low speed fan.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  5. #5
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    In your climate you won't get much out of the 18 SEER. The EER ratings are fairly close, and that's all that matters to you in 100F+ temps. I assume these are Goodman/Amana unit (they are the only one i know of that makes a single stage 16 SEER). From what I can tell, they basically to get 18 SEER, they take the 16 SEER unit, add a high effciency fan motor and a 2 stage unloading valve. They might also use a sightly larger coil. In high temps the fan is running at high speed all the time and isn't that much more effcient in those conditions.

    However, if it still good to have the 2 stage for comfort given how long your cooling season is? IT will also be more quiet most of the time running in 1st stage. Same in heating mode as well. I assume your getting a heat pump. I think you still ahve some heating requirements in winter evenings.


    For a hot dry climate you will want a oversized indoor coil match, and you'll want to oversize the ductwork if possible so you can run at a higher airlfow of 450CFM/ton. That mean a 3 ton unit needs 1350 CFM, as much as a 3.5 ton unit. If you marginal on ductwork, you better off going 1 size smaller and running at a higher CFM. You'll get nearly the same capacity, have longer run times and it will be a lot more efficient.

  6. #6
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by timjimbob View Post
    Single stage is much less problematic. (read- less repairs)

    Never figured into ROI calculations.

    Unlike single stage cooling, seem every manufacture have a different approach to accomplish two stage cooling. Trane uses two compressors, Carrier, reversing compressor and old Lennox, two speed compressor, now unloading compressors are the way. Each have their specific parts and required manufacture training that is confusing.

    Carrier quite bulding the 2 stage Infinity unit with reversing Bristol. They had way too many reliability issues with it and it was probably a slow seller and they had better margins on the unloading scrolls. They only have eth Infinity 17 & 21 unloading scrolls. Trane still makes the XL20i with 2 compressors. But they also have the XL16i and XR16 unloading scroll. I think all other makes use an unloading scroll.

    Again, usually the highest SEER units just add a slightly larger outdoor coil and an ECM vairable speed or usually multispeed condenser fan motor. This does make them extra quiet.
    My Infinity 19 heat pump in low stage is insanely quiet in cooling mode. It almost makes my also very quiet Infinity 17 running next to it seem noisy in comparison.

    I haven't heard of a lot of issues of failures on unloading valves. It a pretty basic solenoid valve. More with reversing valves on heat pumps I think. I wouldn't think the reliabilty is much different on a unloading scroll, which is what most are now.

  7. #7
    Join Date
    May 2013
    Posts
    6
    Thank you for the input!!
    We are comparing 2 Trane systems, the XR15 and the XL16i. The furnace is the XV80. Noise really isn't an issue because right now our air intake is in a small dining room, so almost anything is quieter than it is now. We were wondering if it would save us enough over the life of the investment to make sense in paying for it.

    As for our duct work, we just had it replaced 2 years ago with the mylar R-6. We have some long runs right now, but we are hoping that moving the AC to the attic (much more centrally located) instead of the garage, we should cut down some runs by 40'. Our new longest run should be about 30'. We've been hoping to recycle the current ductwork into our project.

  8. #8
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,015
    Ductwork is a 'package' deal... in it should be planned as a package and NOT patched and pieced together. Ductwork is more important than equipment... as good ductwork produces more comfort and efficiency than which box is attached to it.

    I would START with an energy audit (either a BPI or RESNET certified person) usually the local power co can provide names... sometimes they do them. If they charge extra for a 'room by room' loac calculation, go ahead and do it. They will give you a list of repairs and a 'bang for the buck' in energy cost reduction. Specifically ask them to calculate system sizing after the major home repairs. Note in the midst of this one can get a house 'too tight'... which produces a whole host of other issues. I would specifically ask the energy auditor to explain this.

    After you have done this... find a heating and AC contractor that will work with you and your newly found energy audit information. Remember than design of ductwork and installation of the equipment is more important than the brand. I have seen many a 'high name' system perform poorly... yet a 'economy name' system, installed on proper ductowrk, perform very well (and efficiently).

    In a nutshell.... I am saying do your energy homework FIRST.

    On the equipment... I agree with the other pro's: 2 stage is about comfort and humidity control... it is not about payback... and you really need to be in a VERY hot and/or humid climate to make 18 SEER pay over 16 SEER. The VS furnace is a must IMO... not so much the 2 stage AC. Be sure to get a media style filter... worth it.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  9. #9
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Quote Originally Posted by Wifey View Post
    Thank you for the input!!
    We are comparing 2 Trane systems, the XR15 and the XL16i. The furnace is the XV80. Noise really isn't an issue because right now our air intake is in a small dining room, so almost anything is quieter than it is now. We were wondering if it would save us enough over the life of the investment to make sense in paying for it.

    As for our duct work, we just had it replaced 2 years ago with the mylar R-6. We have some long runs right now, but we are hoping that moving the AC to the attic (much more centrally located) instead of the garage, we should cut down some runs by 40'. Our new longest run should be about 30'. We've been hoping to recycle the current ductwork into our project.
    Tell your dealer you want the XL15I and forget the other choices. Invest in lowering the heat load of the structure, and most important is the proper air flow

  10. #10
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,015
    Quote Originally Posted by motoguy128 View Post
    Carrier quite bulding the 2 stage Infinity unit with reversing Bristol. They had way too many reliability issues with it and it was probably a slow seller and they had better margins on the unloading scrolls. They only have eth Infinity 17 & 21 unloading scrolls. Trane still makes the XL20i with 2 compressors. But they also have the XL16i and XR16 unloading scroll. I think all other makes use an unloading scroll.

    Again, usually the highest SEER units just add a slightly larger outdoor coil and an ECM vairable speed or usually multispeed condenser fan motor. This does make them extra quiet.
    My Infinity 19 heat pump in low stage is insanely quiet in cooling mode. It almost makes my also very quiet Infinity 17 running next to it seem noisy in comparison.

    I haven't heard of a lot of issues of failures on unloading valves. It a pretty basic solenoid valve. More with reversing valves on heat pumps I think. I wouldn't think the reliabilty is much different on a unloading scroll, which is what most are now.
    Rheem/Ruud still uses 2 compressors in their 3 ton and higher 18 SEER units (the 3 ton comes both one and two compressor design).

    Otherwise, as far as I know all the manufacturers use the unloading scrolls except Trane and American Standard (latter is Trane with a different label on it).
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  11. #11
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by second opinion View Post
    Tell your dealer you want the XL15I and forget the other choices. Invest in lowering the heat load of the structure, and most important is the proper air flow
    If the outdoor unit location isn't near a bedroom or a noise sensitive place, save a little more and jsut get a XR15. Same unit without the fancy top. Its' only a shade louder and not as pretty. But it's also shorter.

  12. #12
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,472
    Go with either 15 or 16 SEER unit as the break even on 18 will not be in your lifetime. Most of what we sell is the 14 SEER unit matched to achieve 15 SEER as it's much lower in price than a 16 SEER. We don't recommend two stage outdoor units as they are much more complex, and once out of warranty very expensive to repair! Add that to a really long payback, and does not work out.

  13. #13
    Join Date
    May 2013
    Posts
    6
    I think you all have helped us make the right decision. Thank you so much. This is the largest improvement to our house so far, and with three little mouths to feed we want to make sure we get the biggest bang for our $$. We are going with the company that was the only one to do a load calculation before the estimate.

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