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  1. #1
    Join Date
    Jun 2003
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    120

    oversized. Now what?

    Just curious if I should do anything or just leave the system alone.

    I have a 3-ton Carrier 13 SEER AC unit installed about 5 years ago. The house is 1,100 square foot ranch home (small). I have re-insulated the attic since installing the AC. The AC is combined with my Oil-fired Carrier 84K BTU furnace. The house is in New York State. Lower end of the state.

    I haven't done any load calculations, but I have to imagine that 3 tons is way too much for the home and I am paying much more electric costs than I need.

    Is it economical to switch the AC to a smaller size? Are there more things involved than simply switching the outside unit?

    The furnace is fine, i only use about 350 gallons of fuel oil in a typical winter and the house is comfortable at 67 degrees, so I wouldn't want to replace it.

    The AC is comfortable, but it doesn't remove humdidity as well as it should and I always feel like I am paying for this huge AC unit to run when I may just need a tiny one. But I don't want to switch it out if it will take 10 years to recover the cost or something like that. I only want to switch it out if it is a "no-brainer".

    Duct work in the house consists of one major rectangular duct and then individual 5-inch metal ducts feeding the individual registers. The air for both the heat and ac comes out of the ducts very rapidly. I have one return vent located in a back hallway about 1.25 ft by 2.25 ft (haven't measured it).

    The fan is noisy and also the sound of the air going through the vent is pretty noisy. I have learned to live with the noise however. It is really the energy usage that I am concerned I am using way more electricity than I need to be.

    any thoughts?

  2. #2
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    You need a Pro that can test the static(air flow resistance),and adjust the fan speed ,so you are at 350 cfms per ton,to increase dehumidification.

  3. #3
    Join Date
    Jun 2003
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    120
    Quote Originally Posted by dash View Post
    You need a Pro that can test the static(air flow resistance),and adjust the fan speed ,so you are at 350 cfms per ton,to increase dehumidification.
    I have an anometer (measures air velocity in FPM) at work that I have access to. Can I simply make a rough estimate myself by determining the flow rate in CFM at each individual register and adding them together? Then I can get back to you with what I measure to see if I'm way over or at about the 1,050 CFM that I should be at?

  4. #4
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    Probably won't be that accurate,and if you lower the cfms too much ,you can damage the the equipment,i.e. Compressor.

    It also won't show any air the is lost thru supply duct leakage,and you need 350 cfm per ton across the coil.

    Since it appears to be oversized,this may not help as much as is needed.

  5. #5
    Join Date
    Jun 2003
    Posts
    120
    Quote Originally Posted by dash View Post
    Probably won't be that accurate,and if you lower the cfms too much ,you can damage the the equipment,i.e. Compressor.

    It also won't show any air the is lost thru supply duct leakage,and you need 350 cfm per ton across the coil.

    Since it appears to be oversized,this may not help as much as is needed.
    I just counted in my head, I have 10 registers and 1 return in the house. Does that mean on average I am getting (if set up properly) 105CFM per register? If so, does that sound like a lot of air flow, not enough air flow, or just the right air flow?

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    If they are all the same size, but different lengths, you are not getting the same air flow from each.

    Even the same lengths don't have the same air flow most of the time.
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  7. #7
    Join Date
    Jan 2004
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    Lancaster PA
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    He may already be at 350 per ton.

    Have it checked. if its already at 350 or less. You may want to consider having the A/C replaced with a properly sized HP, so you have a hybird/dual fuel system.
    Tht could easily drop another 100 gallons off your oil consumption. And repay you for the replcaement cost in a relatively quick time.
    Unless oil is cheaper in NY, then it is in PA.
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  8. #8
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    Jun 2003
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    Quote Originally Posted by beenthere View Post
    He may already be at 350 per ton.

    Have it checked. if its already at 350 or less. You may want to consider having the A/C replaced with a properly sized HP, so you have a hybird/dual fuel system.
    Tht could easily drop another 100 gallons off your oil consumption. And repay you for the replcaement cost in a relatively quick time.
    Unless oil is cheaper in NY, then it is in PA.
    I am hardly using any oil right now (350 gallons). People with larger homes are using upwards of 800 to 1000 gallons, so I am not as concerned with the fuel oil usages as I am with the oversized AC.

  9. #9
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    Quote Originally Posted by brewyourown View Post
    I am hardly using any oil right now (350 gallons). People with larger homes are using upwards of 800 to 1000 gallons, so I am not as concerned with the fuel oil usages as I am with the oversized AC.
    350 gallons x $4/gallon = $1400

    What was oil last year? $2.50/gallon?
    350 x 2.5 = $875. This winter you'll spend an extra $525 if the temps are similar to last winter.

    Good luck.

  10. #10
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    Quote Originally Posted by brewyourown View Post
    I am hardly using any oil right now (350 gallons). People with larger homes are using upwards of 800 to 1000 gallons, so I am not as concerned with the fuel oil usages as I am with the oversized AC.
    I understand that.

    And $1,400.00 at 4 bucks a gallon for heat isn't bad.

    But a new A/C may or may not save enough to show a return in a reasonable amount of time.

    A dual fuel heat pump will offset most of the cost of a new unit in heating saving. And still leaves you with the warmer air temp of your oil furnace when its cold ouside.
    And if oil hits 5 bucks a gallon this winter. The ROI is much quicker yet.
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  11. #11
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    Jun 2003
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    Quote Originally Posted by beenthere View Post
    I understand that.

    And $1,400.00 at 4 bucks a gallon for heat isn't bad.

    But a new A/C may or may not save enough to show a return in a reasonable amount of time.

    A dual fuel heat pump will offset most of the cost of a new unit in heating saving. And still leaves you with the warmer air temp of your oil furnace when its cold ouside.
    And if oil hits 5 bucks a gallon this winter. The ROI is much quicker yet.

    I understand now. I had always been told that Heat Pumps were much more expensive and have never even considered them. Where can I find out more about them? Would this heat pump provide air conditioning as well? sorry for being naive, but hopefully this forum can benefit people like me.

  12. #12
    Join Date
    Sep 2002
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    12,195

    How much will a 15/16 SEER HP save over a 13 SEER HP ?

    And yes; I realize that heat pumps are rated differently - but the HP efficiency follows the AC efficiency too - right? <g>

    In terms of heating - how much less will the highest efficiency HP system cost to operate versus the lowest efficiency HP system?

    PHM
    ------------



    QUOTE=beenthere;1921049] . . . . A dual fuel heat pump will offset most of the cost of a new unit in heating saving . . . . .
    QUOTE]
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  13. #13
    Join Date
    Mar 2004
    Posts
    60

    oversized

    1100 sf 3 ton up state ny?????? do you have no windows doors insulation....etc? or do you enjoy your system turning on and off every 4 mins? HELLOOOOOO LOAD CALC.!

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