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Thread: Is is common to upsize evaporator coils?

  1. #1
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    Is is common to upsize evaporator coils?

    Is it common to upsize evaporator coils? Using 3.5 ton inside coil with a 3 ton outside coil?

    It was claimed this increased the efficiency. If so, why don't they come that way to begin with?

    Do those combinations of an upsized evaporator coil affect SEER and EER, and show up in lists of approved tax-credit eligible equipment?

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    yes

    i don't know

    yes, yes

  3. #3
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    Quote Originally Posted by Maikerum View Post
    Is it common to upsize evaporator coils? Using 3.5 ton inside coil with a 3 ton outside coil?

    It was claimed this increased the efficiency. If so, why don't they come that way to begin with?

    Do those combinations of an upsized evaporator coil affect SEER and EER, and show up in lists of approved tax-credit eligible equipment?
    If you look in the AHRI database, you will see that there are often multiple inside coils that will work with a particular outside unit. Some of these don't have the exact same size (I've seen both bigger and smaller), and some of these combos actually pull higher ratings. It's the certification that matters.

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    They don't come that way to begin with because it depends on location and equipment. Larger coils produce better efficiencies for sensible cooling loads. Smaller coils provide better latent cooling. If you live in a very humid area, you might need the smaller coil to provide comfortable cooling.

  5. #5
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    Technically. An indoor coil doesn't really have a BTU rating.

    The BTU rating is a hold over from the old days. Carrier on many of its air handlers. Doesn't use a BTU rating. just a number, like 3, or 4. And both coils may be matched to 2 ton unit.
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    Quote Originally Posted by garya505 View Post
    If you look in the AHRI database, you will see that there are often multiple inside coils that will work with a particular outside unit. Some of these don't have the exact same size (I've seen both bigger and smaller), and some of these combos actually pull higher ratings. It's the certification that matters.
    QFT. This is very nuanced with different coil-air handler/furnace-condensor combination coming out differently. Having looked at probably 100s, there isn't a clear rule of thumb that I can discern. It is very product specific.

    Also note, heating and cooling are different. A combination that offers superior cooling may not offer superior heating.

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    Quote Originally Posted by DavidNJ View Post
    QFT. This is very nuanced with different coil-air handler/furnace-condensor combination coming out differently. Having looked at probably 100s, there isn't a clear rule of thumb that I can discern. It is very product specific.

    Also note, heating and cooling are different. A combination that offers superior cooling may not offer superior heating.

    As spoken by the expert!!

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    but was he correct?

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    Thread Starter
    Thanks for the replies.

    I now understand that an oversized evaporator coil is not necessarily bad, and tends to improve sensible cooling at the expense of latent cooling.

    But since this is on a heat pump, how do I evaluate if the oversized coil will adversely affect the heating?

    If I look at the combination's EER on the AHRC website, is that enough to determine that it is OK?

    I got the feeling they stuck the oversized coil on the proposal because that is just their standard procedure, not because of anything about my load or conditions.

    They first wanted to put in a 3 ton. When I asked why, they mentioned square footage. When I insisted on 2.5 ton, and said I preferred a j-calc instead of square footage based sizing, he said he used WrightSoft to determine my sizing and came up with 2.88 tons. But he did not measure my house, ask about insulation, count windows, or anything else.

    It is not easy to find a company that wants to follow the steps and procedures recommended on this site, at least not in July. Maybe in October.

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    Quote Originally Posted by Maikerum View Post
    It is not easy to find a company that wants to follow the steps and procedures recommended on this site.
    Hey, don't beat yourself up to bad, a lot of those giving the advise probably don't either.
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  11. #11
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    Quote Originally Posted by Maikerum View Post
    But since this is on a heat pump, how do I evaluate if the oversized coil will adversely affect the heating?
    If I look at the combination's EER on the AHRC website, is that enough to determine that it is OK?
    Check the HSPF. 8.5 is good, more is better. Check the heating capacity at 47F and 17F. You should see more than one coil listed for a particular furnace/HP combo, so you can compare the performance of the combos with each coil. There's a lot of good info in the AHRI directory, though it can be difficult to search.

    Quote Originally Posted by Maikerum View Post
    I got the feeling they stuck the oversized coil on the proposal because that is just their standard procedure, not because of anything about my load or conditions.
    Maybe, but if the AHRI numbers are good and it's sized right for your house, you don't really care about their motives. If you spot a combo with a better coil you could ask them about it.

    Quote Originally Posted by Maikerum View Post
    They first wanted to put in a 3 ton. When I asked why, they mentioned square footage. When I insisted on 2.5 ton, and said I preferred a j-calc instead of square footage based sizing, he said he used WrightSoft to determine my sizing and came up with 2.88 tons. But he did not measure my house, ask about insulation, count windows, or anything else.
    If he didn't do any measurements, his Wrightsoft calculation is gargage.
    Remember -> garbage in, garbage out.

    Quote Originally Posted by Maikerum View Post
    It is not easy to find a company that wants to follow the steps and procedures recommended on this site, at least not in July. Maybe in October.
    Yes, but if you do your homework and are confident of the sizing and equipment selections, then the most important thing you need is an expert installer. Like I like to say, "eliminate the variables".

    If you can find a company who can 1) make good sizing calculations and decisions, 2) select good equipment for your home and your needs, 3) and do a good job installing, you have a winner. Personally, I don't have much confidence I can find all three of those in one company, so I'm going to be very involved in the first two, and focus on finding a good installer as my top priority.

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    Quote Originally Posted by garya505 View Post
    Personally, I don't have much confidence I can find all three of those in one company, so I'm going to be very involved in the first two, and focus on finding a good installer as my top priority.
    Smart man! you sound like a realist.
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    Although, item 3 (finding a good installer) will be constrained by item 2 (select good equipment for your home and your needs).

    The problems with item 1 and item 2 are a) good load sizing software is expensive and moderately complex; b) most vendors provide little real product information to consumers and there aren't very good sources to learn how to objectively evaluate the information provided. A lot of the information they do provide is hidden in meaningless marketing terms. Carrier's modulating furnace is multi-stage rather than 3 stage; Trane's compressors are 'Climatuff' whether they are reciprocating or scroll.

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    Quote Originally Posted by DavidNJ View Post
    Although, item 3 (finding a good installer) will be constrained by item 2 (select good equipment for your home and your needs).
    A little more work, yes, but I don't mind, to get what I want. Some installers can get better pricing on some brands, so you have to work with that, but in the end, small differences in equipment pricing are going to be way less important than a good install.

    Quote Originally Posted by DavidNJ View Post
    The problems with item 1 and item 2 are a) good load sizing software is expensive and moderately complex; b) most vendors provide little real product information to consumers and there aren't very good sources to learn how to objectively evaluate the information provided.
    HVAC-Calc is $50, and my calcs on that were confirmed by two contractors who used Wrightsoft. If someone is going to ask why I didn't use one of those contractors, it's because I didn't know much about equipment then and there was so much contradicting information between them (and others), I didn't know what to think (and pricing was all over the map).

    If I can't find the specs myself, the contractor will be required to provide them in advance, or they will be eliminated from consideration.

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  17. #15
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    A large indoor coil sometimes helps in heating, sometimes not. Varies with the match ups.

    A nominal rated 3 ton outdoor unit. May match up to indoor coils rated from 3 to 5 ton.
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    Quote Originally Posted by DavidNJ View Post
    Although, item 3 (finding a good installer) will be constrained by item 2 (select good equipment for your home and your needs).

    The problems with item 1 and item 2 are a) good load sizing software is expensive and moderately complex; b) most vendors provide little real product information to consumers and there aren't very good sources to learn how to objectively evaluate the information provided. A lot of the information they do provide is hidden in meaningless marketing terms. Carrier's modulating furnace is multi-stage rather than 3 stage; Trane's compressors are 'Climatuff' whether they are reciprocating or scroll.

    Can I sell you some 'Corinthian' leather? Or a 'Body by Fisher'?

    The marketing is all psychology based. The marketers have done research after research to determine what sells a product. It may be an insult to your intelligence to think you're so easily 'pigeon-holed' but reality proves that shapes, colors, words can have a significant effect on people and what motivates them to purchase.

    I'd like to have just 1/3 of the business I've quoted over the years. A full blown presentation with full load anaysis included runs 2 to 4 hours. Most people have little or no understanding of the HVAC business so even when they get a proper load analysis, duct analysis and options on equipment from bottom to top, they're still looking for lower prices. Not all or we wouldn't still be in business but the majority by a wide margin. Americans think everything is a commodity. It isn't and good work costs more. Unless people are willing to pay realistic prices for quality work, they'll never get what they realy want.
    If YOU want change, YOU have to first change.

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    Quote Originally Posted by skippedover View Post
    The marketing is all psychology based. The marketers have done research after research to determine what sells a product. It may be an insult to your intelligence to think you're so easily 'pigeon-holed' but reality proves that shapes, colors, words can have a significant effect on people and what motivates them to purchase.

    I'd like to have just 1/3 of the business I've quoted over the years. A full blown presentation with full load anaysis included runs 2 to 4 hours. Most people have little or no understanding of the HVAC business so even when they get a proper load analysis, duct analysis and options on equipment from bottom to top, they're still looking for lower prices. Not all or we wouldn't still be in business but the majority by a wide margin. Americans think everything is a commodity. It isn't and good work costs more. Unless people are willing to pay realistic prices for quality work, they'll never get what they realy want.
    "shapes, colors, words can have a significant effect on people and what motivates them"

    Absolutely true. The auto business, which most of the time is a finance business, is based on that. More than a few buyers get hosed by auto dealers, especially people who can't afford to get hosed.

    The whole sales process here is problematic because the vendors market it as product sale...install a new air conditioner...rather than a system sale...upgrade your HVAC infrastructure that may include a new system. The rebates are on hardware based on published efficiencies promote the hardware sale not the infrastructure change. Does duct even qualify for a rebate?

    The solution in the HVAC issue may not be when you do the sizing but how quickly you can evaluate the customer as one who is likely to choose you over other vendors. 6 hours spent making a sale from two prospects is better than 10 hours spent making a sale from 10 prospects. Or not making one.

  20. #18
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    Is is common to upsize evaporator coils?
    Just to be clear, we are talking about changing the size of the heat exchanger but the expansion device is still precisely matched to the compressor/condenser capacity.

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    Quote Originally Posted by Rabbler View Post
    but was he correct?
    Yes , he was correct. Expert or not.

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