GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Choose Slightly Higher HSPF or save $ upfront as payoff is ~7 years.

ktkcad | Posted in GBA Pro Help on

I’m looking to buy a mini-split for my business office. Seems simple enough but I have 3 basic choices.
15 SEER 9 HSPF at base price for either 115v/230v, simple inverter
21.5 SEER 9.8 HSPF(IV) bp+$300 for 230v, upgraded inverter
21.5 SEER 11.2 HSPF(IV) bp+$320 for 115v, upgraded inverter
I’ve no problem installing 230v vs 115v and it’s only 5′ from the panel.

First, is it even worth paying the $300+ for about a $40/year savings? 9 vs 9.8 or 11.2,

Second, if so is the higher HSPF worth the ‘energy hit’ of 115v (11.2) vs 230v (9.8) for the presumed higher HSPF when we’re actually in Area 1(Seattle WA) vs the units’ tested area IV?

In many ways this is nitpicking. But, I’m self installing (with line evacuation help) and the unit will be an example to clients. So having an educated opinion on these things will help me explain it to my clients.

Thanks so much for your input.


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    Dana Dorsett | | #1

    Area 1? In HSPF terms that would be Florida and Hawaii, not Seattle. Seattle is on the boundary of regions V and IV from an annual heating hours point of view. The modest average temperatures and higher 99% outside design temperatures in the Puget Sound region typically leads to higher than region IV tested efficiency. See:

    Not all HSPF testing is meaningful- the sizing/oversizing factors have to be right to make it a meaningful comparison. Getting the sizing right from a modulation range point of view can mean even HIGHER as-used efficiency, if it can be modulating rather than cycling on/off in heating mode even at out temps north of 50F. To figure this out you have to calculate/estimate the heating load at your 99% outside design temp (typically 25F-28F-ish in King County), and the heat load at +47F (a temperature at which minimum modulated output is tested as part of the HSPF test.)

    If the thing is so oversized for the load that it'll be cycling on/off even at 30F and lower there's no way it'll actually hit it's tested-rated numbers, but if it's still modulating with load at +47F it'll beat those numbers (sometimes by quite a bit) in your climate.

    Sized reasonably most HSPF 10-ish mini-splits will perform with an as-used HSPF 11 in your area, and sized optimally can even beat HSPF 12.

    Also note, for a client's private residence (rather than your business), the payback is in after-tax dollars, even if it works out to 7 years that's a better net ROI than most comparably safe investments.

    So, first things first: Calculate actual heat load at the 99% outside design condition, then again at +47F. Without that information there's no way to correctly size the model or estimate it's as-used efficiency. If you're not going to even attempt that calculation, pick the model that has the lowest modulated output at +47F. If you happen to have an heating history on that office space, it's possible to estimate loads based on fuel use.

  2. Kenny78 | | #2

    As to the "energy hit" those have to be different size eg. 12,000 btu vs 24,000 btu units.

    Watts are watts in single phase applications.

  3. iLikeDirt | | #3

    Assuming your math is right, it's a personal judgment call. Given that the service like of the equipment can be 20 years or more, a 7 year payoff would be a no-brainer for me, but maybe not for you.

  4. ktkcad | | #4

    Thanks Dana. Appears the map I referenced had the 'HSPF Regions' legend/listed backwards. and Yes, Seattle/Puget Sound is basically 'Climate Zone 5'.

    My 99% heat load is 11,200ish BTUs per the WA Energy Code calculator so I've been looking at 'comparable' 12k units from the same brand. +47dF = 5,700 BTUs. Since I'm not needing to keep the 'office' at 70 at the typically coldest times of the day it might seem reasonable to downsize to 9k except that the units' price difference is negligible.

    So...with everything being equal other than the units' published ratings, is it recommended (or not) to use 230v over 115v?, even if the HSPF is 1.4 points higher/better in the 115v unit.

    Thank you.

  5. ktkcad | | #5

    Thanks Ken,

    It's been awhile since I worked directly with an electrical engineer and I may have forgotten a few things about the subtleties of single phases vs triple phases and am currently crossing/shortcircuiting neuron pathways between 230v single phase with triple phase efficiencies.

    Also looks like I should be looking into the requirements for the fed & local rebates...the office is in my home.

  6. Kenny78 | | #6

    Hi Karl, most of the 120v mini-splits I see cap off at 12,000 btus. One consideration if this size is applicable is generator compatibility and/or off grid parts simplification. This might not be a consideration but thought it worth mentioning

    Out of curiosity, what is the upgraded inverter option? What model units are you looking at?

  7. ktkcad | | #7

    Ken, Thanks for the info. I won't be off grid anytime soon but I may have such clients.

    Apparently the inexpensive Pioneer models sold on Amazon have at least 3 levels of inverters. The double to tripled pricing on the Mitsu's and Daikin's are overkill for this particular project's budget.

  8. charlie_sullivan | | #8

    Karl, Dana's advice is good. Iff you can find specs on the minimum heat output, choose the one with the lowest minimum heat output.

    As for the question of whether it matters whether you get a 120 unit or a 240 unit, it doesn't matter much. For the same power draw, the 120 unit will have more current. So if you have a long wire run and you want to split hairs, the small power loss in the wiring will be more in the 120 unit. But if the higher efficiency advertised for the 120 unit is real, that would make a bigger difference. Mostly it is a question of whether you happen to have one already available where you are going to locate it without running power all the way from the circuit breaker box.

  9. Dana1 | | #9

    Again, to compare between models you need to dig up the minimum-modulated output at +47F. The as-used HSPF can vary pretty dramatically. If , your load at +47F is going to be about 5700 BTU/hr. Any mini-split you install needs to be able to modulate WELL below 5000 BTU/hr, ideally it would be under 3000 BTU/hr @ +47F to be able to modulate well during Seattle's long shoulder seasons. Upsizing to a 1-ton simply because it's only a few bucks more can be a step down in as-used efficiency it's minimum modulation is much higher than the 3/4 ton, and pushes over 4000 BTU/hr.

    The Mitsubishi -FH09NA can 12,200 BTU/hr of heating capacity at +17F, and can modulate down to 1600 BTU/hr @ +47F, which means it will modulate with load nearly constantly, and will beat it's HSPF13.5 numbers pretty soundly in your location:

    From a reliability and local service resource point of view I can vouch for them in your area (I have several relatives heating with FE-series Mistubishis in your neighborhood.)

    Most 115V units are third tier units with lower quality/reliability. If you have to repair/replace it within 5 years any savings on up-front cost evaporates. If you want something lower cost than the latest greatest Daikin or Mitsubishi, the older Fujitsu 9RLS2 is good for 12000 BTU/hr @ +17F, modulates down to 3100 BTU/hr @ +47F, and sports an HSPF of 12.5, which it will beat pretty soundly in your climate:

    They're getting pretty hard to find, but should be cheap from wholesalers clearing older stock.

    The older Mitsubishi FE09 is also a possibility, delivering 12,500 BTU/hr @ +17F, modulating back to 3000 BTU/hr @ +47F, testing at HSPF 10.0 (which it beats by a mile in your local climate):

    Again, should be pretty cheap if you can find one in stock.

    At a lower price point (from an arguably second-tier vendor, but still pretty good), the current LG LA120HYV1 delivers 12,000 BTU/hr @ +17F, and modulates down to 1023 BTU/hr @ 47F, and would beat it's HSPF of 12.0:

    Service support varies for LG in the US- I'm not sure how good it is in your area compared to Mitsubishi (holds more than 1/3 of the market in WA) and Fujitsu (also pretty big.)

  10. ktkcad | | #10

    Excellent information. Thank you and I will update this when I have pulled the trigger on the project.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |