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My 20 year old heat pump gave up the ghost. With summer here, I need something soon. I've had companies give me bids over the weekend, both with great reviews on yelp and Google.

Guy #1 was selling me on a $22k unit. It's a high end model with maximum energy efficiency and all the variable speed and dehumidification options. He said I'll see a big drop in my energy bill going from a 14 to 22 SEER unit. And that these new models will quietly hum away all day at low speed, never hammering the fans and compressor hard when it clicks on making them last a lot longer. Sounds good so far, loving it all except for the price.

Guy #2 was selling me on the lowest price unit at $8k. His point was my duct work is old, at least 20 years from the last HVAC replacement and possibly 50yo from when the house was built. He says all old duct work is too leaky to realize the gains from the high efficiency unit, though he'd sell me that if I really wanted. I haven't noticed any gaping holes in the ductwork, but also unsure how well it's insulated.

I trust both guys, and don't believe #1 is trying to make a quick buck off me. I reached out to him for his perspective on the old duct work, but haven't heard back yet.

Basic info: 2,300sf tri-level house with a previously working 3ton unit. There's a couple mini splits in the converted attic and lower level rooms as supplemental HVAC to create zones.

How much of an impact does the old ductwork have? How do you determine that?

Update 1

  • Aprox 60% of the ductwork is inside the envelope
  • The system being replaced is 3.5 ton
  • Located in central Virginia (US). Around here we need AC about 6mo a year, and heat the other 6mo, with a lot of mild days in the spring/fall. Summer regularly get's to the upper 90's for 3 months.

Update 2

  • Went with a Bosch 15 Seer BOVB-60DN1-M15 and paired air handler. It has the benefits of inverter motor on the outdoor unit while not being as expensive or complex as a full communicating system.
  • Outdoor unit location is 12' from my deck, and a top concern was that outdoor unit noise levels making making the deck unusable in the summer.
  • Major concerns I've read about this unit is the noise during heating mode in the winter, mitigated by a mass damper on the line set, and logic boards getting fried on both indoor and outdoor units (esp outdoor) mitigated by a surge protector.
  • Also, customer service might(?) require repair technicians to be on the phone to troubleshoot for warranty claims, but unsure how accurate this remains. If you don't have cell service or land line, that may complicate things.
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2 Answers 2

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Ignore the ductwork. It does matter, but it will affect costs no matter what system you install. However, as long as the ductwork is inside the house, the cold air is still getting into your house and, while you lose a little efficiency it just isn't that big a deal.

The real issue is Total Cost of Ownership or TCO. With HVAC, as with many things, you can only approximate this as you don't know how long either unit will last. The $22k unit may last longer than the $8k unit because it is better built. Or it may not last as long because it is more complex and things break. Or (more likely) it will last as long but with more repairs along the way due to complexity. But it is a total guessing game. A typical range is 15 to 25 years. You pick a time (# of years), usage (based on historical degree days unless you have a better idea), energy cost (based on efficiency) and compare:

  • Unit cost + (expected yearly usage x electricity cost x years)

That doesn't account for comfort differences, so all else being equal that would give the edge to the variable-speed unit. Will you save $700 ($14k / 20) per year in energy with the more efficient unit? That is the question.

Somewhat related is heating. Similar calculations apply, though your coldest expected weather is a factor as well. If you have to switch to "emergency heat" frequently that will significantly increase heating cost. If you don't then the more efficient cooling unit will almost certainly be more efficient at heating as well.

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    The comment: "However, as long as the ductwork is inside the house, the cold air is still getting into your house " is absolutely NOT true. If your duct work is leaking conditioned air into your attic or crawlspace, it's just wasting money and energy. How much it's costing you requires an Energy Audit to decide if it's worth the money to Seal and Insulate areas of the house.
    – Earl
    Commented Jun 18 at 4:48
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    @Earl -- I think manassehkatz was getting at "inside the conditioned envelope" Commented Jun 18 at 5:46
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    "A typical range is 15 to 25 years." While mine lasted nearly 30 years and my next door neighbor finally gave in and replaced his after 40 years. You might just get more life out of it.
    – FreeMan
    Commented Jun 18 at 17:02
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Regardless of which contractor that you go with, the first step should be to get a 'Home Energy Audit' that includes a Blower Door / Duct Leakage test.

Your 22 SEER level system could have as low as an 12 SEER rating if you have a 30% Duct Leakage issue:

Factory versus Actual Efficiency

(From: https://www.priorityenergy.com/service/cost-duct-leakage - Note that this is a Commercial site so take the actual percentage loss with due scepticism)

Here are some articles on the subject for your review: https://www.energyvanguard.com/knowledge/diagnostic-testing/duct-leakage/

https://basc.pnnl.gov/resource-guides/total-duct-leakage-tests#edit-group-description

https://www.energyvanguard.com/knowledge/diagnostic-testing/duct-leakage/outside-duct-leakage-test/

Deep Dive into Duct Testing: https://energy.nv.gov/uploadedfiles/energynvgov/content/Duct_Leakage.pdf

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    ps. Another consideration is what type of refrigerant are they recommending as R-410A systems can no longer be manufactured after Jan 1. 2025. There is no deadline on maintenance but just as R-22 is now very expensive, R-410A might be more expensive as it becomes less available so R-32 or R-424B might be a better choice long term (note - I am NOT an HVAC expert, just currently looking into the same questions that you are)
    – Earl
    Commented Jun 18 at 4:59
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    This is a great call out! Thanks. From what I'm seeing, R32 is better; it's been used in Europe and Asia for decades, it's not proprietary and is cheaper, has as much heat transfer capacity, and is a single gas. R424B is patented and a blended gas made up of R32 + something else. When repairing the blended gas systems, you can't just top them up since the balance of the blend might get out of balance. You have to replace the entire volume of gas Good rundown here: youtube.com/watch?v=RQnKPb6i0oI
    – UncleChef
    Commented Jun 18 at 10:43

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