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  1. #1
    Join Date
    Aug 2011
    Posts
    9

    New construction is a 2 ton Lenox too small?

    Hello,
    NOT an HVAC pro here, just some guy buying a house and feel the 13 SEER 2 Ton Lenox AC unit they are installing is a bit too small. I'm working on the particulars like BTU, model etc... the contractor is a bit elusive at the moment.

    The house is a new 2 story, with 2300SQ Ft living space. In Denver Colorado.

    This house with the Bonus room.. http://www.pulte.com/communities/co/...ns/walden.aspx

    Thoughts? I just really like cool... and don't need it over worked..

  2. #2
    Join Date
    Sep 2002
    Location
    I don't know
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    2,903

    Thoughts? I just really like cool... and don't need it over worked.
    Sounds like the builder did a load calc.

    Will the house face north/south or east/west?

    Based on the floor plan, link it doesn't appear to have a lot of window surface area, so a 2 ton unit may do the job.

    If you're really nervous about insufficient capacity, get the builder to upsize by 1/2 a ton above what the calc indicates. (just make sure the duct system is designed accordingly)


    Thoughts? I just really like cool... and don't need it over worked..
    The worst thing you can do to a compressor is start it.

    Running continuously during the day poses no problem as long as it maintains the setpoint.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  3. #3
    Join Date
    Sep 2002
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    I don't know
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    2,903
    Denver's average january temp is well above freezing - have you considered a heatpump instead of a regular a/c?
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  4. #4
    Ask others in the neighborhood with similar houses and compare yours to theirs - it seems like you don't have complete information which makes it hard for anyone on here to help you out.

  5. #5
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,215
    One system on a 2 story home is just asking for trouble unless it's zoned properly. For $300k I'd expect 2 separate systems...

  6. #6
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Here's another way to look at it. What do you expect your electric bill to be wiht all of the insulation and such? A 15 SEER, 2 ton unit, sized correctly in the hottest months at $0.12/kw-hr will still use $80-90 in electricity. It might be even less in Denver since it's cooler at night in the summer and a LOT less humid.

    In Denver, I really don't think AC capacity will be an issue. Worst case, in a hot spell, you might have to set the temp slightly lower and run it 24 hours and let it catch up at night and in the morning. But overall you're better off a little small than a little big.


    If it were my money... and I only needed 2 tosn of capacity but had 2 floors, I'd either zone it and get a 2 stage AC and furnace or I'd get a minisplit heat pump with 4 ducted units and have 4 zones with 6000-9000 BTU's in each zone, and use a gas fireplace for auxillary heat as well as back-up heat if hte power goes out.

  7. #7

    Confused?

    I hear this same thing quite often, and to answer your question a 2 ton unit can correctly cool a 2300 square foot home if the heat gain calculations and sizing was done correctly. You can take 5 homes of the same size in the same city and will get different calculations for each. There is no set "quick" measurement. Also, while you strive to CORRECTLY size every unit, if you are going to miss, you want to miss on the small side with air conditioning. This would allow the unit to run longer and pull more humidity out of the air (dehumidification is 75% of air conditioning), whereas too large a unit would not sufficiently dehumidify the conditioned space. Bigger, in this case, is definately NOT better...

  8. #8
    Join Date
    Jun 2009
    Location
    Albuquerque NM
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    2,485
    Quote Originally Posted by 54regcab View Post
    One system on a 2 story home is just asking for trouble unless it's zoned properly. For $300k I'd expect 2 separate systems...
    If I had a 2-story house it would have 2 zones or 2 separate systems. Chances of getting good temperature control both upstairs and downstairs are slim otherwise.

    The cost of fixing this later will be WAY more than doing it right to begin with. Production builders don't really care. I know a guy who just spent $10K to fix the system in his new house for this very same reason.

    If it was me, I'd see if the builder would allow me to pay the HVAC sub the difference to do it right.

  9. #9
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,500
    Gotta agree with most posters, if you have a full two story with only one system then you need to zone it. If you have a HVAC contractor who won't or does not know how to zone, then talk to the General Contractor and see if you can get another expert opinion. Remember, you are the one paying the bill and it's darn near impossible to change once the system is in and covered up. Heat rises, and cold air falls, so two story homes without two systems or zoning have wild temp. differences from floor to floor. Lots of times all the general living space will be on the lower floor and the bedrooms on the upper floor which makes the AC problem even more aggravating. Not any fun trying to sleep in a pool of sweat!!!

  10. #10
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    I am *not* saying 2 tons isn't enough, but the only real downside I can see is mis-matching duct sizes if the owner wants to upsize in Denver. Keep in mind here there is little or no humidity problem in Denver, and the temperature swoops down pretty low overnight... at least by my standards. I am a homeowner in S. TX where we have heat and humidity in large quantities. In an area where humidity control is problematic, I would want to follow ACCA Manual J much more closely -- my own house is due to downsize AC when the present one has to be replaced.

    What would be wrong with getting a 1-1/2 ton unit for each of the two stories? Or ducted minisplit(s)? Indeed it would cost more but I am assuming the owner is willing to pay for a meaningful upgrade. Being more in the middle of what others expect, will help with eventual resale too.

    I submit that the most important thing to ensure is that duct sizing is appropriate. Pushing 25% more air thru ducts than designed for, sounds like trouble.

    Just some amateur thoughts.

    Best of luck -- Pstu

    P.S. If you have a smaller unit on each floor, likely the usage will be assymetrical and there would be better humidity removal than with one larger unit. Not that Denver needs it much.

  11. #11
    Join Date
    Jun 2009
    Location
    Albuquerque NM
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    2,485
    I like with the idea of using two 1 1/2 ton units (or maybe smaller). Make them both heat pumps. Then, put a gas furnace and a VisionPRO IAQ thermostat on the lower unit for a dual fuel set-up. Add a humidifier and you've got a nice set-up.

    Yes, it would cost more, but if I was buying a $300K house, it would be worth it to get good comfort. I'd be a little unhappy in a new house if the HVAC system couldn't control the temperatures properly on both floors. But maybe that's just me.

  12. #12
    Join Date
    Sep 2002
    Location
    I don't know
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    A 2 story house can be cooled properly without zoning, provided that the duct system is well designed and a 2-3F difference is tolerable.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  13. #13
    Join Date
    Jun 2009
    Location
    Albuquerque NM
    Posts
    2,485
    Quote Originally Posted by amd View Post
    A 2 story house can be cooled properly without zoning, provided that the duct system is well designed and a 2-3F difference is tolerable.
    I'm sure it can be done, but I haven't been in one that was truly comfortable yet. If you ask the residents, they just shrug their shoulders and say that's the way it is, like they don't know it can be much better.

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