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Thread: 10 seer or 13?

  1. #1
    Join Date
    Feb 2006
    Location
    Aurora, IL.
    Posts
    29

    Question

    Hello everyone,

    I've just moved into my new 1600 s.f. home with a Rheem RGPN 05eauer gas furnace. I had the unit prewired for a/c and the hvac contractor installed a 13 seer-3 ton adp "A" coil with txv. (Now I know better) I didn't go with their a/c install beacuse they were grossly overpriced. I did check with them and they said the house requires a 2.5 ton unit. Some of the experts here think the coil is oversized, and I agree. I am running a manual J to get my calcs and it looks like a 2 ton will suffice, but I am curious about one thing. Up here in Illinos, cooling is not the biggest need and I would like to know if I can use a properly sized 10 or 12 seer condenser versus paying the premium for 13. It's my thinking the short cooling season here does no justify the cost. Is it ok to do so with my setup or am will it cause problems later?

  2. #2
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    Have your coil matched to a condenser. Nothing wrong with 10 seer with your short A/C season IMO.Payback with the 13 would be awhile in a cool climate,unless you have really high electric rates. There are formula's to find out...



    P.S. You'd get much better advise if you were a Yankee fan.
    If everything was always done "by the book"....the book would never change.

  3. #3
    Join Date
    Feb 2006
    Posts
    89
    I am located here in chicago, and would like to point out that 10 seer units are phased out this year at my supply house. Especially in rural areas due to rolling blackout conserns in the heat of the summer.

    Now on to the next question. An oversized unit poses a couple of problems in your home. one problem is that the coil acts as a dehumidifier as well as cooling the air. this is the main feeling of comfort when coming in from a hot and humid day. If the unit is oversized, then it wont take as long to satisfy the thermostat, meaning that it wont dehumidify as much of the air that it would be designed to whhithin a given cycle.

    secondly, there is a possible reason fo a service call for an iced up coil, because there wouldn't be enough air passing through the coil that it was designed for. This causes the freon temp. to drop, and the moisture from the humidity in the home to freeze on the coil causing an ice dam.

    Your on the right track by doing a load calc on the home. also make sure that the cond. unit is matched to the coil, and piston units are fine too, just make sure that you read the piston chart that comes with the condensor and replace coil piston if necessary.(biggest reason why piston units work improperly is because installers ignore these charts!)

  4. #4
    Join Date
    Feb 2006
    Location
    Aurora, IL.
    Posts
    29

    Talking

    Good one.

    Are you saying I need to replace my indoor coil? I thought having a larger coil was better, or will that cause the unit short cycle? Is it a big deal or just preference?


    By the way.....

    Albert Einstein is at a party and asks one of the guests, “What is your IQ”
    “165”
    “Great, we can talk about nuclear physics and cosmology”
    After a few minutes of lively discourse, another party guest tries to get in on the conversation.
    Einstein asks him, “What is your IQ”
    “64”
    To which Einstein replies: “GO YANKEES!”

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,594
    That coil probably rates to 1.5 to 3 ton units, especially with the TXV. My guess it will be perfect for a 2.5 ton outdoor unit.

    Doesn't make sense, though, that the house can heat with such a small furnace yet needs 2.5 tons to cool it? Did anyone do a load calc?

  6. #6
    Join Date
    Jul 2005
    Posts
    435
    I thought 10 to 12 SEER is no longer available due to fed regulations starting in 2006?

  7. #7
    Join Date
    Feb 2006
    Location
    Aurora, IL.
    Posts
    29
    I think 2.5 tons is too much too. I am currently doing a Manual J and it looks like 2 tons might be better suited IMO. Can I still use the existing coil?

  8. #8
    Join Date
    Feb 2006
    Location
    houston,tx
    Posts
    5

    Talking

    After you do a load cal, have your coil matched to the condensor. A 10 seer unit is fine as long as the equipment is matched.Try to get an ARI match to see if you are getting the right seer and btu rating.It doesn`t matter what seer rating you are using if it is not sized correctly.Undersized or oversized equipment will be not be energy efficient no matter what seer rating you decide to use. Also comfort will be compromised.

  9. #9
    Join Date
    Feb 2006
    Posts
    89
    I personally don't like retrofitting coils with condensers. even txv coils. mainly because the txv valve is adjustable and it was factory set for use with the matched cond. unit. If you change the cond. unit you would have to readjust the txv to accomodate, and I don't know of a field tech yet with the knowledge to do so. It took me most of the afternoon on the phone with the manufacturer when I did this last. Coils are pretty inexpensive compared to the cond. unit, I would replace both. Otherwise if the installer does the retrofit properly, you will probably have to pay an unbelieveable amount for labor while he tries to properly superheat the unit.

  10. #10
    Join Date
    Feb 2006
    Location
    Aurora, IL.
    Posts
    29
    OK, so if I get my coil replaced also, what do I do with the one I have now? It came with the a/c prewire on the house and I would't have any other use for it. Or should I contact the manuf. and see if it can be used? I know some of you have certain preferences on what to use and how, but I am trying to find out if replacing the coil is utterly necessary.

  11. #11
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    6,328
    First get the heat load done.

    If it comes in at 2-tons then I don’t see the need to change the coil.

  12. #12
    Join Date
    Feb 2006
    Location
    houston,tx
    Posts
    5

    Smile

    If you stay with the original 2.5 ton cond,then your coil will be fine.That said,if all the calcs are saying that you need a 2 ton then you are oversized and problems may arise in the future.The question you have to ask is how important is the comfort level that you want.All the responses you have recieved are correct.The one thing that has to be known is if you use a 2 ton cond, then the coil will problably be to large. If its a 2.5 ton then you will be ok. To be absolutely sure if you coil will work,call the coil`s manufacture and ask then what condensor will match up if you don`t want the expense of changing both coil and condensor.

  13. #13
    Join Date
    Feb 2006
    Location
    Aurora, IL.
    Posts
    29
    I'm getting confused. It's ok, it's not ok. What do you mean by comfort level? Do I want to be cool on a hot day? Ablsolutely! Cooling is important to me, the heating is for the wife. (I moved here from Florida) I just emailed the manuf. and waiting for a response and will keep you posted. Are we talking a huge differencein performance if I went with a 2.5 ton unit in lieu of 2 ton to make it work or a little annoyance?

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