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SEER Value

Benjamin Katydid | Posted in Energy Efficiency and Durability on

Our contractor has two Carrier units, both 3 ton.

– 2 stage 17 SEER

– 5 speed 19 SEER

The 19 SEER unit is about $1,300 more and I’m wondering how to quantify the value. There are at least two ways to look at it. Will the 19 SEER unit provide any benefits at all over the 17? Over what time period would the 19 SEER unit become cost neutral?

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Replies

  1. Expert Member
    Zephyr7 | | #1

    Yes, the 19 SEER unit has some advantages in terms of operating costs. How much those savings will be worth to you depends entirely on how often the unit is likely to run, which depends entirely on the climate zone and number of cooling degree days for your specific location.

    The short an general answer is that the farther south you go, the more likely the higher SEER units are to be cost effective for you. If you're in a more northern heating-dominated area, the benefits of the higher SEER units may not make sense after considering their higher initial cost.

    Bill

  2. Benjamin Katydid | | #2

    Thanks Bill. I'm learning how to calculate the net present value of an investment. Here's an amateur stab at the required monthly savings.

    - assume 10 years since that's what they'll warranty
    - assume 5.75% cost of equity...because my credit card rate would be much much higher
    - assume 3.0% inflation...although we could be facing less inflation in the next 10 years

    Annual equivalent cost = $1,400 / { 1/(.0575 - .03) * [1 - (1.03/1.0575)^10] } = $166
    Can the 2 more SEER and 3 more speeds save me $166 per year or 166/12 = $14 per month? Probably so. Yeah?

    Another stab at this calculation, since I'm making wildass guesses anyway. All the same assumptions...

    Annual equivalent Rental = $1,400 / { 1 + 1.03 / (.0575 - .03) * [1 - (1.03/1.0575)^9] } = $157
    Can the unit save $157/year or $13 per month? Probably so.

    We're just outside of Houston. We live inside an actual sieve of a leaky house. I spend money on AC and dehumidification. We're gonna get the nicer unit, methinks.

  3. Benjamin Katydid | | #3

    Let's relick this calf with some different rates.
    - assume 10 years since that's what they'll warranty
    - assume 15.75% cost of equity...because I could inject the $1,400 into a weak market and make it flip
    - assume 3.0% inflation...although we could be facing less inflation in the next 10 years

    Annual equivalent cost = $1,400 / { 1/(.1575 - .03) * [1 - (1.03/1.1575)^10] } = $259
    Does 2 extra SEER and some variable speeds stand to save $259/year or $22/month?
    I don't know. It's not that much money really. I can't even begin to list all the ways I've frittered away more money. Chic-fil-a! Specsonline.com!

    So it's not exactly a financial decision, $20/month. Maybe it's a comfort question. Will the 19 SEER 5 speed make us $20 more comfortable every month?

  4. Jon R | | #4

    Some more modulating AC equipment doesn't fully modulate the fan to match the compressor - meaning that dehumidification suffers and you are less comfortable. Also, sometimes a high SEER rating is achieved by doing less dehumidification. I'd say "don't generalize - read the specs carefully", but I've never seen manufacturers provide sufficient data.

  5. Benjamin Katydid | | #5

    Carrier's Infinity line is supposed to deliver better dehumidification. That is according to Carrier, so the claim may or may not be worth anything.
    https://www.carrier.com/residential/en/us/infinity/advantages/

    One concern that I have is the unit may be oversized. From what I can tell, too-big matters less for variable speed units. Do yall know of any thermostats out there that I can program to kick on at 75 and run til 68? I do this manually right now and it seems to help with humidity.

    1. Jon R | | #6

      > better dehumidification

      It does appear that their "IdealHumidity" does it right, controlling fan speed as directed by humidity.

      > too-big matters less for variable speed units

      It depends, when it comes to dehumidification, I see lots of examples of the opposite.

  6. Josh Durston | | #7

    Assuming your air handling and controls solution modulates to match the compressor and/or humidity levels there are advantages beyond cost to the modulating unit.

    Matching the capacity to the load, will result in longer runtimes. Longer runtimes often translate into more even temperatures throughout the home, especially for rooms that tend to be more volatile temperature wise.

    Inverter units are more friendly to solar with batteries or generators because of the lack of the starting inrush current.

    1. Jon R | | #11

      Sometimes, but note that the primary determinant of room temperature variation is the thermostat (hysteresis and any cycle time limits). Between room variation is another thing - modulating AC units have increased variance in duct losses, creating an increase in room-to-room temperature deltas.

  7. Walter Ahlgrim | | #8

    The best way to know is to model your house with your weather using your electric rated and enter the bid installed costs into the free BEopt computer program and let it pick the winner. Be sure to find and watch the training videos.

    https://beopt.nrel.gov/home

    Sorry if I sound like a broken record. The number of variables in the equation makes the back of an envelope calculation a wild guess. But the biggest factors is time any financial payoff will likely come in years 10 thru 15 and most people move long before that.

    Walt

    1. Benjamin Katydid | | #12

      Thanks Walt. This is a really helpful resource.

  8. Expert Member
    Zephyr7 | | #9

    Be careful using future or present worth calculations. I remember having to do that in a class way back in college. At the time (as now), part of my buisness was dealing in used equipment to save money. I always thought it funny when they would state in the book what the future value of the equipment would be when sold at end of life. It is VERY difficult to know what that might be. I have often “bought” used air conditioning equipment from datacenter facilities for the cost of removal. What this means is that we “pay” the current owners of the equipment by removing the equipment from their facility. Sometimes we’ll have to give them $1 for legal reasons to close a sale, but otherwise they didn’t really make money on the equipment, they just saved money over having to contract to remove it themselves. There is a lot of guesswork with any of these “what’s it worth at some other time” calculations.

    I think you can configure the ecobee thermostat to do what you want, but you have to do it by setting a temperature with a big deadband, or with timed setpoints. It’s a very flexible thermostat and I’m very happy with the several that I own.

    In your southern climate the higher SEER unit is likely to make financial sense. In my area (southeast Michigan), they often don’t. When I’ve helped out friends around Baltimore, where their cooling season is most of the year, the higher SEER units always make sense.

    If you house is super leaky you’d do well for yourself to do some air sealing work. Sometimes air sealing work will result in even more savings than a more efficient HVAC system. There is a lot of info on this site regarding where to look for leaks. Go after the largest leaks first.

    Bill

  9. Benjamin Katydid | | #10

    There's no market for used equipment here that I would know about without special insider's info, so the unit will have no salvage value when we're done. The unit we're having removed will be worth $0 to us because we won't have access to buyers. Plus it's old and nobody would buy it anyway.

    I have definitely targeted the leaks for destruction, time permitting. My little research has not turned up any contractors who know how to seal leaky houses. The closest we've gotten is a nice couple who will do a blower door test. They won't seal anything.

    We gotta modify the HVAC for other reasons. We're gradually converting sections of our house to airbnb style lodging for workers in our heavily industrial community. They need to be able to control the climate in their apartments and we're trying to do as much ductless as we can. As you probably know, most every house out here uses ducts in the hotass attic. I'd like to get away from that because I'll still be toting the light bill. It's not clear how I'd be able to go ductless (or eliminate attic ducts) in our main unit, which includes 2br, 1ba, and an open living, dining, kitchen. We're gonna continue to use cental with attic ducts for that space unless I find a skilled contractor with some building science background and nontraditional design chops...really really soon. That's unlikely.

    1. Expert Member
      Zephyr7 | | #13

      You should consider converting your attic to conditioned space. Sometimes this isn’t very difficult to do, but it depends on the structure and accessibility of your particular attic.

      Note that you can almost always get scrap metal value for your old equipment, but probably under $50, likely well under. That’s still better than the trash guys pay, and metal salvage is a greener option too.

      Bill

      1. Benjamin Katydid | | #14

        I would love to convert the attic. That would be ideal, I think. After Hurricane Harvey flooded us, I geeked out on building science. The conclusion that I reached back then was that an attic conversion is 100% the path we'd pursue if this was gonna be our forever home. Tis not, so we won't. I'm still in love with the idea, though. And the idea that builders could simply stop putting ducts in the hot attic.

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