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  1. #1
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    should the A-coil size match the condenser unit size?

    So I am replacing an old HVAC system in a condo. Got quotes from two contractors so far. Both quoted 2 ton condenser (same size as the one that will be replaced), one guy quoted a 1.5-2 ton A-coil, while the other guy quoted a 3 ton A-coil. What are the factors the determine the A-coil size? Should the A-coil size match exactly the condenser unit size?

  2. #2
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    A two ton AC can have a dozen different coils that are a SYSTEM match. For example a 3 ton coil with a txv on a 2 ton AC increases the efficiency up to an additional 2 SEER. It also would shift more of the 24000 btu towards temperature change and less towards humidity removal. Part of the SEER rating of the system is also the type of blower the furnace has. Bottom line is the coil is chosen to match the requirements of SEER and sensible/ latent heat transfer for your home .

  3. #3
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    Quote Originally Posted by martyinlincoln View Post
    A two ton AC can have a dozen different coils that are a SYSTEM match. For example a 3 ton coil with a txv on a 2 ton AC increases the efficiency up to an additional 2 SEER. It also would shift more of the 24000 btu towards temperature change and less towards humidity removal. Part of the SEER rating of the system is also the type of blower the furnace has. Bottom line is the coil is chosen to match the requirements of SEER and sensible/ latent heat transfer for your home .
    So a 2 ton coil with a txv on a 2 ton AC will NOT increase the efficiency? I thought the increase in efficiency is due to the txv, not the tonnage of the coil. Why a higher tonnage coil is beneficial is the part that confused me.

    BTW, the furnace is not going to be replaced. So the new coil and AC is going to use the old blower. The condenser is rated something like 13-14 SEER, should I replace the blower as well?

  4. #4
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    A text increases efficiency over a piston/orifice.

    Coil size changes efficiency of heat transfer and/or humidity, like martyinloncoln stated.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
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  5. #5
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    All we use are txv . Back when we used both fixed orifice and txv for metering devices the difference was around 1/2 a SEER. The txv gives better humidity control when the AC runs so IMO it's more for comfort than efficiency.

  6. #6
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    Ask them to provide you something like this to prove a match, and it will tell you your SEER and EER rating.

    https://www.ahridirectory.org/Home/D...MXaB6qQujL0jCG

    OD units can be rated at whatever SEER the web-site says but it's the indoor selection that determines your SEER and EER. It's a team effort. The OD section is just one part of the equation. It can even be less ( SEER ) than the OD label.

    I personally like the piston metering device on the lower SEER units, for there simplicity and troublefree operation.

    If they can not provide a AHRI number, chances they are proposing a non matching system at your expense. Keep your furnace if you want to stay around 13-14.5 SEER. Anything higher you'll need to replace the furnace with a ECM blower and a higher rated SEER OD unit.

    Make sure to register your system as manufacturer warranty decreases significantly if never registered. California and Quebec need not to be registered to receive maximum manufacturer warranty.
    Last edited by Bazooka Joey; 05-30-2019 at 12:57 PM.

  7. #7
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    Still confused!

    To make things simple, with a 13-14 SEER, if not using the txv, just use the old school piston or orifice metering device. With a 2 ton outdoor condenser unit, should the A-coil be 2 ton or 3 ton?

  8. #8
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    As examples only, used Goodman, as their web-site is very user friendly with a lot of info.

    https://www.ahridirectory.org/Home/D...6gtLTCZuJJSifJ

    This system uses a 2 ton OD unit, but needs the 2.5-3 ton piston metering device to get to 14 SEER using the GSX14

    https://www.ahridirectory.org/Home/D...p1/2DGmrxRkr+E

    This is the GSX13 2ton OD unit using a 1.5-2 ton piston metering device to get 13 SEER plus the EEP which is a time delay on the blower motor.



    You need to remember they make 13 SEER models and 14 SEER models, both can achieve higher SEER, they will state " up to a certain SEER "

    Typically 13 SEER and even 14 SEER are bare bone models.

    13 SEER for Northern regions

    So again ask for the AHRI number from these Contractor to see if they can match a system to your requirements.

  9. #9
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    Quote Originally Posted by Bazooka Joey View Post
    As examples only, used Goodman, as their web-site is very user friendly with a lot of info.

    https://www.ahridirectory.org/Home/D...6gtLTCZuJJSifJ

    This system uses a 2 ton OD unit, but needs the 2.5-3 ton piston metering device to get to 14 SEER using the GSX14

    https://www.ahridirectory.org/Home/D...p1/2DGmrxRkr+E

    This is the GSX13 2ton OD unit using a 1.5-2 ton piston metering device to get 13 SEER plus the EEP which is a time delay on the blower motor.



    You need to remember they make 13 SEER models and 14 SEER models, both can achieve higher SEER, they will state " up to a certain SEER "

    Typically 13 SEER and even 14 SEER are bare bone models.

    13 SEER for Northern regions

    So again ask for the AHRI number from these Contractor to see if they can match a system to your requirements.

    So using a higher tonnage A-coil achieves higher SEER, right? In the examples you listed, both the outdoor units are 2 tons, but a 3 ton A-coil gets 14 SEER, while a 2 ton A-coil gets 13 SEER.

    If that's the case, I should go with the contractor who quoted me the 3 ton A-coil.

    BTW, what is the "time delay on the blower motor"? Again, I plan to use the old blower, I don't think it has the "time delay", but what is it anyway?

  10. #10
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    " both the outdoor units are 2 tons, but a 3 ton A-coil gets 14 SEER, while a 2 ton A-coil gets 13 SEER"

    You didn't read the post closely, one is a 13 SEER rated OD unit, the GSX13

    The other ( with the 2.5-3 ton coil ) is a 14 SEER rated OD unit GSX14

    Did not see using a 2 ton ID coil with a piston with the GSX14 gives you 14 SEER, but then again that's just one brand that was referenced.

    Have theses guys work for their money and provide you the AHRI numbers, least they can do to get your business.

    Time delay is pretty common nowadays, it means the blower motor starts at a predetermined amount of time after the A/C compressor or furnace starts. Also it's not uncommon to have a time delay before the blower motor stops after the A/C or furnace stops.


    " So using a higher tonnage A-coil achieves higher SEER, right?"

    Yes that's true but it's one piece of the puzzle, other things that increase SEER is a TXV metering device as discussed already, and a ECM blower motor on a furnace or Air Handler and a higher SEER rated OD unit. But in those instances your talking probably around 15 SEERS OD unit rated on up.
    Last edited by Bazooka Joey; 05-30-2019 at 04:21 PM.

  11. #11
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    Quote Originally Posted by Bazooka Joey View Post
    " both the outdoor units are 2 tons, but a 3 ton A-coil gets 14 SEER, while a 2 ton A-coil gets 13 SEER"

    You didn't read the post closely, one is a 13 SEER rated OD unit, the GSX13

    The other ( with the 2.5-3 ton coil ) is a 14 SEER rated OD unit GSX14

    Did not see using a 2 ton ID coil with a piston with the GSX14 gives you 14 SEER, but then again that's just one brand that was referenced.

    Have theses guys work for their money and provide you the AHRI numbers, least they can do to get your business.

    Time delay is pretty common nowadays, it means the blower motor starts at a predetermined amount of time after the A/C compressor or furnace starts. Also it's not uncommon to have a time delay before the blower motor stops after the A/C or furnace stops.


    " So using a higher tonnage A-coil achieves higher SEER, right?"

    Yes that's true but it's one piece of the puzzle, other things that increase SEER is a TXV metering device as discussed already, and a ECM blower motor on a furnace or Air Handler and a higher SEER rated OD unit. But in those instances your talking probably around 15 SEERS on up.

    Got it, thanks a lot!

  12. #12
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    Quote Originally Posted by chrisoffice View Post
    Got it, thanks a lot!
    You responded before I made changes, last sentence changed to 15 SEER rated OD units on up. Those SEER, EER are difficult to achieve in the real world. Just like in the old days when car manufacturer said that you will get a particular MPG.

  13. #13
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    Quote Originally Posted by Bazooka Joey View Post
    You responded before I made changes, last sentence changed to 15 SEER rated OD units on up. Those SEER, EER are difficult to achieve in the real world. Just like in the old days when car manufacturer said that you will get a particular MPG.
    On a related question, again using your example, here are the 2 ton and 3 ton A-coil to go with the GSX13 and GSX14 condenser units,

    GOODMAN CAUF1824A6, 1.5 to 2 Ton, W 13 x H 16 1/4 x D 20 1/8, Uncased Evaporator Coil
    GOODMAN CAUF3636A6, 3 Ton, W 13 x H 19 1/2 x D 20 1/8, Uncased Evaporator Coil

    Now the question is, these two coils look exactly the same, the 3 ton one is a little higher than the 2 ton one (3 1/4 inch higher). So where does the difference in tonnage come from? Does the few inch increase in height alone account for at least 50% increase in the tonnage?

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