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  1. #1
    Join Date
    Nov 2018
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    6
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    Advise on sizing

    Good morning, replacing existing residential system for my 1,305 sq. ft. home on long island NY. (new system RA16 with RH1V2417 variable speed air handler). Received multiple proposals with the majority recommendations being 2.5 ton systems with lower SEER. The preferred contractor feels the 2 ton system would be adequate due to the higher SEER and would do better dehumidifying the residence. It is a single story home with four occupants, adequate insulation and open floor design but are near the water and it tends to get muggy.

    I understand the square footage is close to the cut off point to upgrade to a 2.5 ton system but would rather not spend additional cost for the bigger unit with lower SEER, had a 2.5 ton system previously (15 years old) and cooled the home nicely but tended to just kick on and off in the hot days of summer and not sure how adequately it dehumidified the home.

    Would love to get this forums professional input and opinion.

    Thank you.

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    9,155
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    What is important the occupants? Basement house? How important is occasional warm temperatures and high %RH evening/rainy days? Are you perfectly comfortable with your current system? Concerns about occasional mold/musty/dust mites? Slightly under sized get you slightly better %RH during low loads.
    If you want control of the temperature during high cooling loads and additional occupants, slightly over-size. If you want total control of the %RH during evenings and rainy days, add a small whole house dehumidifier like a Ultra-Aire 70H. You can even turn off the a/c when the home is unoccupied and maintain <50%RH throughout including the basement. This eliminates the possibility of mold and dust mites regardless of the rainy weather.
    Keep us posted on your thoughts.
    Regards Teddy Bear
    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"

  3. #3
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    20,849
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    Manual "J" calculation for Sizing
    Manual "D" for Ducts
    manual "S" For Equipment selection.

    Anything else is just a guesstimate!

  4. #4
    Join Date
    Nov 2018
    Posts
    6
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    Thread Starter
    Thank you, occupants fluctuate between 3-4 people, basement with exterior entrance, very open design with just three bedrooms off main living area. Everything ducted from attic. Classic Long Island weather, occasional 95 plus degrees but tend to stay in the upper 80’s during summer and tends to be muggy. As mention old system has no problem keeping up and keeping the home cool but in my opinion was in no way efficient, would kick on hard to bring temperature down than shut off. Liked the idea of higher SEER and variable speed but was concerned with the two ton. Could push up to 2.5 but substantial cost increase.

    Like the idea of dedicated dehumidifier as mentioned.

  5. #5
    Join Date
    Aug 2002
    Posts
    2,144
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    A 2 to a 2 1/2 ton should not be a significant cost difference. If the 2 ton guy is significantly cheaper than the 2 1/2 tons then I would be concerned that he may be cutting corners or not properly installing the equipment.

    The only proper way to size a piece of equipment has already been mentioned by pec.

    Manual J, duct evaluation to manual D and system selection to Manual S.

    Don’t look for the cheapest cost, find the guy that will perform all the calculations and perform the best install. A cheap install may cost significantly more in the long run if they are cutting corners by not performing the proper calculations and not specifying the proper components, who knows if they will install and setup the products correctly.

  6. #6
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    20,849
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    Quote Originally Posted by cleaver97 View Post
    Thank you, occupants fluctuate between 3-4 people, basement with exterior entrance, very open design with just three bedrooms off main living area. Everything ducted from attic. Classic Long Island weather, occasional 95 plus degrees but tend to stay in the upper 80’s during summer and tends to be muggy. As mention old system has no problem keeping up and keeping the home cool but in my opinion was in no way efficient, would kick on hard to bring temperature down than shut off. Liked the idea of higher SEER and variable speed but was concerned with the two ton. Could push up to 2.5 but substantial cost increase.

    Like the idea of dedicated dehumidifier as mentioned.
    Basements should NOT be part of the main system Completely different Heat Load / Loss. Generally on the island you need heat and a dehumidifier for a basement.

    Small Minis work well 95% of the time

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