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  1. #1
    Join Date
    Feb 2009
    Posts
    19

    Need ASAP Advice on Two-Stage vs. Single Stage new A/C and Furnace (Bryant)

    I am getting a new A/C unit, Coil and Furnace installed this Thursday. Originally, I was going with the Single Stage 16 SEER model because of cost, But the more I read the more I wonder if it's worth the extra money to bump up to a two-stage model.

    Details:
    House is 2,336 sq ft (plus finished basement)
    Current A/C is a 4 ton, builder grade house built in 2000, so likely a very low SEER, maybe 10 or less??
    We do have uneneven temps in 2 upper bedrooms as well as morning room in kitchen (south facing with big windows)
    We live in MD, so hot/humid in summer, and can be pretty cold in winter

    Option 1:
    Bryant Preferred System
    A/C Model 126B, 16 SEER (actual model is 126BNA048) **Note, the contractor did some calculations yesterday and feels that we probably should get a 3.5 ton instead of 4 ton
    Furnace - Plus 80x Model 313 (actual model is 313AAV048090)

    Option 2:
    Bryant Evolution System
    A/C Model 187B, 16-17.5 SEER (actual model is 187BNA048) Note: Contractor said we'd stick with 4 ton for this system
    Furnace - Plus 80v Model 315 (actual model is 315AAV048090)
    Cost - The cost of the two-stage model is $1,100 more than the single stage unit

    Questions:
    1. Is there an actual efficiency/energy savings that results in cost savings by going with the two-stage vs. single-stage?
    For example, will I get my $1,100 back in savings in 5 or 10 years (or less?) by going with the two-stage model?
    2. Or is the only benefit, simply a better comfort level with the 2-stage, but no cost savings?

    Ultimately, I'm trying to justify the $1,100 cost increase with the 2-stage over single-stage systems...

    I've read several postings and the information doesn't seem clear as to the accurate answer to this, so any help is Greatly appreciated!!

  2. #2
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,535
    Pricing is not allowed. Mods will delete before long!!! As for your question I would suggest variable speed (2) stage gas furnace for comfort and energy savings.

    The variable speed operation in cooling mode helps in controlling humdity better and adds much more comfort along with energy savings and reduction in noise.

    (2) stage gas heat allows for more even temps in winter months and gives you (2) speeds for heating which can be a god send when it's not that cold out staying in low stage and when gets colder outside will use 2nd stage.

    Of course the system needs to be sized properly along with ductwork supply and return for any system to work propely wether it be a variable speed or fixed speed fan.

    Just remember that while the upfront cost is a little more for variable speed this is long term dession that will affect you for years to come. It hard to put a price on comfort. So my vote goes for variable speed (2) stage with outdoor unit all sized properly.

  3. #3
    Join Date
    Feb 2009
    Posts
    19
    Woops...Yes I understand about pricing, I thought that meant total system price, but I was just showing price difference which doesn't tell too much and is useful to help determine justifying cost difference.

    Thanks for the info. It seems that it's hard to pinpoint if the extra cost will actual be recouped or not. I understand you get what you pay for, thus paying more gets you more comfort. I'm just trying to determine if that extra cost is worth it financially.

    When I told our contractor that I keep the thermostat at 72 in summer, he thought that was very low, thus indicating that it possibly indicates that we have a lot of humidity in our house (not sure, but very likely) and the system has to work quite hard to make the house comfortable. He says we should be comfortable at a higher temperature like 76 or so and still feel very cool.

    The better control of humidity via the 2-stage unit sounds appealing (as well as the more evenly spread out heat/cooling across entire house).

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,538
    Quote Originally Posted by bkapla1 View Post
    Thanks for the info. It seems that it's hard to pinpoint if the extra cost will actual be recouped or not. I understand you get what you pay for, thus paying more gets you more comfort. I'm just trying to determine if that extra cost is worth it financially.

    When I told our contractor that I keep the thermostat at 72 in summer, he thought that was very low, thus indicating that it possibly indicates that we have a lot of humidity in our house (not sure, but very likely) and the system has to work quite hard to make the house comfortable. He says we should be comfortable at a higher temperature like 76 or so and still feel very cool.

    The better control of humidity via the 2-stage unit sounds appealing (as well as the more evenly spread out heat/cooling across entire house).
    My experience is that low speed cooling provides lower air flow which intern decreases uniform air flow and distribution in the hard to reach parts of the home. When operating on the low speed, the large coiling coil takes longer to load with moisture and start dripping to the drain.
    During low/no cooling loads conditions with +60^F outdoor dew points, there is not enough sensible cooling load to the 2-4 lbs of latent moisture load from the occupants and infiltration/ventilation. Take the upcharge for the two speed a/c and install a whole house dehumidifier in the home. Units like the Ultra-Aire whole house dehu remove 3-4 lbs of moisture per hour with lowering the temp in the home. They are able to maintain <50%RH with out any cooling load, even with the a/c off. Your basement will be the nicest space in your home when maintain at <50%RH.
    Set the temp you want and %RH you want with minimum utility cost.
    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
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    Quote Originally Posted by teddy bear View Post
    My experience is that low speed cooling provides lower air flow which intern decreases uniform air flow and distribution in the hard to reach parts of the home. When operating on the low speed, the large coiling coil takes longer to load with moisture and start dripping to the drain.
    This can hold true for marginal duct systems, which is the caution I bring up with any kind of two stage or modulating HVAC system. If the ducts are crap, variable capacity systems can be problematic in terms of comfort and energy cost.

    That said, I have a two stage system in my own house - on good all-metal ductwork running through an attic protected by a reflective roof - and it works great in terms of dehumidification and comfort cooling. Even lately, with reduced sensible load due to an unusually wet and cool two days for July, the system cycles sufficiently to control humidity and keep internal heat gain in check. For the typical spider flex duct system in overheated attics common in my area, however, I wouldn't be so confident on a good outcome.
    • 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.

  6. #6
    Join Date
    Feb 2009
    Posts
    19
    This is exactly what I meant, no clear cut answer as opinions differ.

    Our house is 13 years old and was built by Ryan. The contractor seemed to thinks that the ducts looked fine (mostly rectangular metal ducts and not the "spider" type that you mentiond). He also mentioned that the ducts were quite large so the newer higher system should have no problem being efficient in our home.

    Although a central dehumidifier sounds nice, I don't want to front the extra cost for that at the moment.

    So, I'm still unsure of which option makes sense.

    If the two-stage works well, but Only from what it sounds under optimal conditions, then perhaps without knowing if we have optimal ductwork, etc. if it them makes sense to front the extra cost up front if we are not going to reap the benefits of a more comfortable living space AND a more efficient system (e.g. to recoup the extra costs).

  7. #7
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,538
    Quote Originally Posted by bkapla1 View Post
    This is exactly what I meant, no clear cut answer as opinions differ.

    Our house is 13 years old and was built by Ryan. The contractor seemed to thinks that the ducts looked fine (mostly rectangular metal ducts and not the "spider" type that you mentiond). He also mentioned that the ducts were quite large so the newer higher system should have no problem being efficient in our home.

    Although a central dehumidifier sounds nice, I don't want to front the extra cost for that at the moment.

    So, I'm still unsure of which option makes sense.

    If the two-stage works well, but Only from what it sounds under optimal conditions, then perhaps without knowing if we have optimal ductwork, etc. if it them makes sense to front the extra cost up front if we are not going to reap the benefits of a more comfortable living space AND a more efficient system (e.g. to recoup the extra costs).
    The extra cost of the two speed will go a long way to cover the cost of a small whole house dehu. You can spend the extra money on the two speed and add the dehu later.
    Occupants in a home adding moisture and and adequate infiltration/ventilation outside cool damp air to change the air in the home in 4-5 hours makes the home damp during low/no cooling loads conditions. A simple single speed a/c combined with a small efficient whole house dehumidifier provides the desired temp and %RH for health and comfort. The operating cost will be much less than overcooling a home in attempt to maintain low humidity. In addtion to costing more, few techs now how to setup and maintain complication multispeed a/cs.
    In green grass climates many experts and a/c distributors are providing WH dehus to make homes more comfortable and efficient.
    Good Luck and keep us posted.
    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"

  8. #8
    Join Date
    Feb 2009
    Posts
    19
    One more question... I decided on the Single-Stage Furnace and A/C unit.
    However, the contractor just called to let us know the single-stage furnace was on backorder, so they will be bumping the furnace up to the Evolution 2-stage series (no addt'l charge to us).

    My question is this, if our A/C unit is a single-stage unit and the furnace is a two-stage unit, what exactly does that mean to us now....
    1. Does this mean that the A/C will still run at a single speed, so the two-stage furnace provides no benefit while the A/C is running?
    2. Does this mean that the heat will in fact utilize the two-stage technology and we will reap the benefits with the Heat part Only now?

    Just curious since it is now a mixed system.

    Thanks in advance!

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