Page 1 of 5 12345 LastLast
Results 1 to 13 of 53
  1. #1
    Join Date
    Mar 2005
    Posts
    56
    Carrier 38TRA024 (2 ton outdoor unit)
    Carrier 58STA070 (3.5 ton indoor unit (gas burning)

    I had the above equipment installed in a 950 sf brick home w/ full basement and with full sun exposure. 1 out of three estimates that I got for this house recommended a 1-1/2 ton system while the other two recommended 2 ton systems.

    My question has not so much to do with the outside 2 ton unit which I am happy with, but it is the 3.5 ton gas furnace indoor unit that was installed. I was under the impression from the guy that installed the system that I was getting a 2ton system. After installation he told me that he installed a larger inside unit. His reason was that he wanted to get the air from the ceiling registers all the way to the floor. At the time he called it a "larger unit" ..after looking up the model # on the Internet I learned that it was a 3.5 ton inside unit. When he said "larger inside unit I figured it was like a 2-1/2 ton inside unit....not something as powerful as a 3.5 ton inside unit. Remember ...this is a 900 - 950 square foot house.

    I know that in some situations it is OK to put a slightly larger inside unit compared to the outside unit, but a whole 1.5 ton extra???? Ina 900-950 sqft house???

    Please reply with your thoughts on this.




  2. #2
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    If your 58STA070,ends in -16,then it can handle a 3.5 or 4 ton A/c.They make an ,_08 and -12,which are 2 ton and 2.5/3ton airflows.



    You are likely getting more cfms(airflow then required,which reduces humidity removal ,in the cooling mode.


    If it's a -16,it move 1045 cfms ,on low speed ,at .80 ESP(static/resistance).At 1.0 ESP,on low,it's 740 cfms ,so it could be correct,but that's a very high ESP.

    We don't know what the ESP of your duct system is ,without that or some other measurement,we don't how many cfms it is moving.Standard is 400 cfms per ton,so around 800 is expaected,less in humid areas,more in dry areas,is a good idea.

    What model coil did they install?

    [Edited by dash on 06-30-2005 at 11:11 AM]

  3. #3
    Join Date
    Jun 2005
    Posts
    64
    ive never heard of the indoor coil being more than a 1/2 ton larger than the outdoor not a master but 6 yrs experience and a degree

  4. #4
    Join Date
    Jun 2005
    Posts
    64
    your a coil is gonna absorb way more heat than the condenser can get rid of, higher pressures and temps, shorter equipment life.

  5. #5
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    I think/thought he's refering to 3.5 tons of air flow.

  6. #6
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,850
    Originally posted by coco
    your a coil is gonna absorb way more heat than the condenser can get rid of, higher pressures and temps, shorter equipment life.
    None of the above it true! But what do I know I don't have a degree only experience.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,770
    Originally posted by mrbillpro
    Originally posted by coco
    your a coil is gonna absorb way more heat than the condenser can get rid of, higher pressures and temps, shorter equipment life.
    None of the above it true! But what do I know I don't have a degree only experience.
    You old dog.


    A 3.5 ton indoor coil won't harm a 2 ton outdoor unit, provided the metering device is sized for the outdoor unit.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  8. #8
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    i have done this on ocasion at the ocean where the sun and wind load is tough calles for a 2 ton cooling but air flo is need to push. as long as you have the coorect size piston or txv it will work well as was said earler
    the installer probably felt you need the air flo more then btu

  9. #9
    Join Date
    Mar 2005
    Posts
    56

    message to dash

    Originally posted by dash
    If your 58STA070,ends in -16,then it can handle a 3.5 or 4 ton A/c.They make an ,_08 and -12,which are 2 ton and 2.5/3ton airflows.



    You are likely getting more cfms(airflow then required,which reduces humidity removal ,in the cooling mode.


    If it's a -16,it move 1045 cfms ,on low speed ,at .80 ESP(static/resistance).At 1.0 ESP,on low,it's 740 cfms ,so it could be correct,but that's a very high ESP.

    We don't know what the ESP of your duct system is ,without that or some other measurement,we don't how many cfms it is moving.Stansard is 400 cfms per ton,so around 800 is expaected,less in humid areas,more in dry areas,is a good idea.

    What model coil did they install?
    Evaporator coil model #: CK3BXA024017AAAA

    Model # of indoor unit: 58STA070-12... looks like I am alright since you say models ending in -12 are rated for a 2 ton coil

    Here is some more info on the indoor unit
    Seire: 120
    -Manufacture date of indoor unit: 2/2005
    -Motor HP on indoor unit: 1/3

    -Wires on indoor unit to modify blower motor speed: black - high, blue- medium-low, red - low
    -I currently have the cooling side on the blue wire and the heating side on the red wire

    ...even when 76 degrees outside I am unable to get the system down to 72 it just runs and runs and runs for well over an hour ...it will get to 73 ,but no further. The only way I can get it to stop running is to set it up to 75. The air coming from the registers is somewhat cool...but seems like it could be colder

  10. #10
    Join Date
    Mar 2004
    Location
    Gone
    Posts
    5,340
    Your furnace has a 3 ton blower in it designated by the -12 in the model number.

    Your coil is a 2 ton coil.

    Here is your CFM at .5 ESP (external static pressure)

    High : 1200 CFM
    Med-High : 1140 CFM
    Med-Low: 1050 CFM

    CFM at .6 ESP (external static pressure)

    High : 1125 CFM
    Med-High : 1075 CFM
    Med-Low: 990 CFM


    Even if you put your cooling on the med-low tap, you will still be at over 500 CFM per ton at .5 ESP which will not give you good humidity control.

    Your contractor needs to learn a little more about design rather than, “I wanted the air to get to the floor”.

  11. #11
    Join Date
    Mar 2005
    Posts
    56
    Originally posted by madeinusa
    Your furnace has a 3 ton blower in it designated by the -12 in the model number.

    Your coil is a 2 ton coil.

    Here is your CFM at .5 ESP (external static pressure)

    High : 1200 CFM
    Med-High : 1140 CFM
    Med-Low: 1050 CFM

    CFM at .6 ESP (external static pressure)

    High : 1125 CFM
    Med-High : 1075 CFM
    Med-Low: 990 CFM


    Even if you put your cooling on the med-low tap, you will still be at over 500 CFM per ton at .5 ESP which will not give you good humidity control.

    Your contractor needs to learn a little more about design rather than, “I wanted the air to get to the floor”.

    what should I do.... should I have him replace the inside unit with the correct part?

  12. #12
    Join Date
    Feb 2005
    Posts
    344
    That would be a good start. Generally a good idea to stick with OEM approved equipment matches.

    Good luck...

  13. #13
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Testing Total external static of the furnace ,is the only way to know .If it's .8 or above ,the -12 is the better choice,.7 or below the -08 is the better choice.


Page 1 of 5 12345 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event