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Community and Q&A

Efficient HVAC with only electric

jeffshero | Posted in Energy Efficiency and Durability on

Good morning,

I recently moved into a home on the south shore in the Boston area and am interested in improving on the electric resistance baseboards that we currently have.

Our home is about 2000 square feet and a split level with about 1200 sf on top floor and 800 finished sf on bottom floor. We have original fiberglass insulation (assuming R11 or R13) in the 2×4 walls and double batting in most of the attic so about R36 or so. Also, we have 18 single pane windows (with storms), 2 sets of double paned sliding doors and 1 larger single pane bay window. We are also about to have air sealing and weatherization done which should help seal the house better. We are also in the works to putting solar on our roof with SolarCity. Finally, we have a wood fireplace in the upstairs living room and a propane fireplace in the downstairs family room (connected to a 100 lb tank that we own).

I have called many different local HVAC companies and have not found a suitable solution. I was originally interested in a high velocity system (spacepak or unico) for the ease of duct work to the bottom floor and the better looking registers. Everyone that I have spoken to though has almost immediately told me that this is a bad idea because it couldn’t handle a 2000 sf system efficiently enough with a heat pump.

One HVAC company recommended putting in a large (300 lb?) propane tank and using a lennox SL280V variable speed gas furnace, conventional ducting in the attic, and keeping the baseboards in the basement. This seemed ridiculous for $18.5k because it is not very efficient and is not a whole home solution.

A 2nd company must have thought it wasn’t worth working on as they didn’t give me a quote.

A 3rd company suggested putting in either an air source heat pump system (30-40k installed) or a geothermal heat pump system (45-60k installed with a 30% tax credit). They said that the variablity would come in whether we wanted traditional or high velocity duct work and also on how nice of an air handler/condenser system we would choose). It seems to me that it would take a very long time for us to recover any expenses at that cost though.

A 4th suggested traditional ducts for the first floor, a mini-split system for the bottom floor, and multiple condensers (he was mentioning the need for lots of heat load here and 90,000 BTUs and 7-8 tons of capacity). That again, is not a single home solution and seems to be high for BTUs and tons necessary from what I am reading on other systems that folks have built.

I wonder if anyone has any ideas. In particular, I have started to read a lot about multi-split systems here on greenbuildingadvisor. The condensers that I hae been looking at online look like they have BTU capacity of 20k or 30k which seems like I would need several of them which would eliminate the cost savings it seems to me. I greatly appreciate any thoughts or advice.

All the best,

Jeff S.

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  1. GBA Editor
    Martin Holladay | | #1

    You provided lots of information. Here is some advice:

    1. First, get your weatherization work done. Pay attention to reducing air leakage. If possible, add insulation to your attic.

    2. Once your weatherization work is done, get a Manual J (design heat loss) calculation performed by someone who knows what they are are doing (like an energy consultant).

    3. Use that design heat loss figure when designing your heating system.

    I'm adding your ground-source heat pump quote ($45,000 to $60,000) to a file I keep on my desk, labelled "Reasons why it's nuts to install a residential ground-source heat pump."

    You should be able to heat your house with one ductless minisplit downstairs, and a ducted minisplit upstairs. Good luck.

  2. jeffshero | | #2


    Thanks tremendously for your input. It is always nice to validate that you are not crazy. I will get the manual J post weatherization and get a bunch of quotes for a split system.

    Is there a that you would say that I should have ducted upstairs? Is it more efficient or less costly to install than the ductless?

    Again, thank you so much for your thoughts and help.

  3. GBA Editor
    Martin Holladay | | #3

    I don't know the layout of your house. Older homes with multiple bedrooms can be hard to heat with a single minisplit unit, unless you don't mind leaving your bedroom doors open all day, and unless your family is flexible about room-to-room temperature differences.

    The better your thermal envelope -- the best envelopes would have R-30 to R-40 walls, triple-glazed windows, and airtightness levels approaching 1.5 ach50 or less -- and the more flexible your family is concerning room-to-room temperature differences, the more likely you would be satisfied with a single ductless minisplit for the whole floor.

  4. Expert Member
    Dana Dorsett | | #4

    A "typical" 2000' ranch house + full basement in coastal MA with clear storm windows and at least R11s and some attic insulation will come in with a heat load of maybe 40,000 BTU/hr @ +10F if the foundation has no insulation, but closer to 30,000 BTU/hr with an insulated foundation and some air sealing. This sounds like it might be a "raised ranch", with the lower level being partly below grade, with a cantilievered overhang for the second floor(?). (If that's correct some attention to the air sealing & insulation of the cantilevers is in order, a common leak point on that type of construction.)

    The 99% outside design temp in Weymouth is +11F, Taunton's is +9F, Boston's is +12F. Don't let anybody put a thumb on the scale and design to 0F or something just because it get's that cold at least once per decade.

    A 1-ton single-head ductless mini-split like the Fujitsu AOU-12RLS2 or Mitsubishi MSZ-FH12NA can deliver about 13-14,000 BTU/hr even at +5F, which probably more covers the load for your lower level load. If it turns out the downstairs load is under 12,000BTU/hr , dial back to the 3/4 ton versions, the MSZ-FH09NA or AOU-9RLS2, which are both cheaper & more efficient. With a fairly open floor plan, a single head ductless will do quite well.

    A typical 1-ton name-brand mini-split like these runs ~$4K, installed, maybe $3500 for a 3/4 ton.

    For the upstairs it kind of matters what the floor plan is. A dedicated mini-duct cassette system like the Mitsubishi SEZ/SUZ is more efficient than multiple head ductless systems, and can split the output between several rooms, if the cassette/air handler be located somewhat centrally to keep the duct runs short. The SUZ-KA18NA.TH can put out about 12,000 BTU/hr @ +10F, which probably covers the lions share of the above grade load, but you may need more than one cassette, or maybe a 3/4 ton mini-split + a mini-duct cassette, or use the baseboards as the "Hail Mary" back up to manage the whole upstairs on the five coldest days of the year. Room by room heat load analysis would be important for figuring out what does & doesn't work.

    The raw hardware cost on the 1.5 ton -KA18 is under $3K, the installation cost depends a bit on the duct design & implementation issues (hopefully avoiding the attic, but if in the attic, built out with an an air sealed insulated decking over it keeping it inside the home's continuous pressure & thermal boundary,) but I'd be shocked if it ran much over $9K. for the top floor's solution.

    Add it all up and you're still only looking at $12K, $15K at the outside, and if it's sized correctly in your climate it will run nearly as efficiently as typical geothermal installations, a combined seasonal average coefficient of performance in the mid-3s, without the high upfront cost and design risk of a geothermal solution that might be only marginally higher efficiency best-case, and possibly even less efficient.

    Anybody recommending a 90,000 BTU/hr solution for that house even in the "before" position should just plain get out of the business, since that is about 2x oversized even for the unimproved version of the house, and could be 3x oversized for the "after" picture.

  5. jeffshero | | #5


    Thanks so much (again). I don't think I clearly stated my question. I was wondering why a ductless system downstairs and a miniduct upstairs as opposed to a ductless in both. I wasn't questioning that we would need something for both. We have small children so we would definitely want the extra availability to ensure that they are always as comfortable as can be. It seems that Dana has indicated that the miniduct is more efficient than a ductless with several heads which would make sense as to why you recommended it.

  6. jeffshero | | #6


    Thank you so much as well. That is a lot of information and I greatly appreciate it. I just did a bunch of research based on the information that you provided and feel much better informed for having posted my question here in addition to being much more able to make an intelligent decision to save energy and costs.

    You are correct, our home is a raised ranch although we do not have the cantilevered overhang. I really appreciate the advice on what temp to measure towards. We are actually a bit closer to the water than Weymouth so likely aiming at 11 or 12. I'd prefer not to keep the baseboards at all as they're somewhat of an eyesore (at least to me) and was hoping that the propane fireplace on bottom floor and wood fireplace on main floor would serve as 'hail mary' but it seems like perhaps that is a bad idea. We likely don't have any other option besides the attic for any ductwork. Could it possibly be better to go ductless upstairs as well so we can avoid the unconditioned duct issue altogether or is it significantly less efficient with multiple 'heads'?

    I have just called two more HVAC companies from Angie's List and ensured that they perform a Manual J. Additionally, I'll inquire with the air sealing/weatherization company whether they would be able to add insulation to our walls despite the fact that they are already filled with fiberglass.

    Thank you again - so incredibly helpful.

  7. GBA Editor
    Martin Holladay | | #7

    Q. "I was wondering why a ductless system downstairs and a miniduct upstairs as opposed to a ductless in both."

    A. I was guessing that, since your lower floor is smaller than your upper floor, and since Contractor #4 already suggested that a ductless minisplit would work downstairs, that a ductless minisplit would probably work downstairs, but (due to the greater area upstairs) probably wouldn't satisfy your family upstairs. So I suggested a ducted minisplit upstairs.

    Q. "It seems that Dana has indicated that the miniduct is more efficient than a ductless with several heads."

    A. A ductless minisplit with a single head is the most efficient way to go, as long as it doesn't lead to comfort complaints. A ducted minisplit is less efficient than a ductless minisplit. I'll take Dana's word for it that a multi-head ductless system is less efficient than a ducted minisplit -- but the landscape is changing all the time, because manufacturers are introducing new models, so it may be hard to generalize on that point.

  8. Expert Member
    Dana Dorsett | | #8

    A "multi-split" is a multi-zoned ductless system where a single compressor serves multiple heads or cassettes of different sizes & types. This is somewhat less efficient than the dedicates SEZ/SUZ single-cassette ducted mini-splits. The explanation for this is that with only one cassette of a known size, the control algorithms for the single mini-duct cassette can be optimized- the size of the cassette capacity is always going to be in the correct proportion to the compressor, and it's a known cassette type that is fully characterized.

    With multiple heads or cassettes on a single compressor the compressor is sometimes way oversized when say, a single half-ton head is calling for heat at 25% of it's maximum output. The compressors do modulate with load, but a 1.5 or 2-ton compressor doesn't run efficiently at 1/4 ton of load. Then there is the control algorithm issues for serving multiple types of heads at different modulation levels, etc. They're getting to be pretty good at this, but it's just a harder engineering problem than slaving a single head type & size to an appropriately sized compressor.

    The single head mini-splits with a wall-coil heads can be ~20% more efficient than the dedicated single-cassette ducted mini-splits, and 25% more efficient than the very best muli-splits. This partly due to the fact that there is no duct back-pressure while operating, and the cross section of the air path through the wall unit is large compared to that of a mini-duct cassette. Like the dedicated single cassette versions, the algorithms only have to be optimized for one type & size of head.

    If the rooms upstairs are not all doored off from a common area you may be able to get by with a single wall-coil type mini-split, but code requires that all rooms be able to hit 68F at the 99% outdoor design condition, and if a doored off room has much window area it may need supplemental heating to get there. A separate head for the doored of rooms is not usually called for, since say, a bedroom's load is very rarely over half the output of a 3/4 ton mini-split. Unless the design load is 2/3 of the max output of the head it won't run as efficiently. If the load is 1/3 the output of that head the hit in efficiency is significant, as is the hit in comfort, since it will only cycle on/off at low speed introducing a significant standby loss, rather than spending most of it's time modulating with load.

    So, it all starts with a room-by-room heat load calc. Sharpen your pencil, and be aggressive about it- no thumbs on the scale such as under-rating your R-values or window U-factors just because you're not sure. The difference between R13 walls and R11 walls isn't very much, but it adds up if you make cautious estimates over the whole thing, then you have to up-size the equipment to something that covers that marginally overestimated load. The estimate might be only 15-20% oversized from reality, but the next equipment step from there might leave you 35-40% oversized. If you're aggressive in your assumptions and count every last plug load & sleeping dog's output, when you then go to the next step-size on the equipment you'll still have margin, just not 35-40% margin (like you really needed enough heat pump to handle -15F in your location?) It's counter to how most people usually think about it, anxious to be oversized "just in case", but in fact right-sizing the equipment results in both higher efficiency and higher comfort.

    In the unusual once in a quarter century deep coolth events you can buy a sweater, or sit in front of your propane burner.

  9. charlie_sullivan | | #9

    How much of a hurry are you in? If you are not in a hurry, do the envelope improvements first. Then get set up to monitor your electricity usage for heat. And spend a year heating with the old electric baseboard heaters. That will give you much more accurate sizing data than any calculations could.

    And find someplace to post a review of that guy who wanted to sell you a 90,000 BTU/h system and warn others to stay away from him!

  10. srenia | | #10

    Mini split systems are expensive and full of maintenance issues. 26 inch pthp system are trouble free, require no expertise to install and pay back near a decade before a mini split. Mini splits are a niche product and should be treated as such in the USA.

    Having said this after loosing 7k on a rental by trying mini splits. PTHP came to the rescue. Mini splits look good on paper, but are a nightmare in real life.

  11. Aaron Birkland | | #11

    My own opinion (based almost entirely on advice gleaned from various posts and comments at GBA) is that individual room loads are very important to understand if you want to reason about comfort with point-source heating (ductless mini splits), or are deciding whether you need a more expensive and less efficient ducted solution.

    There are many stories of mini-splits performing very well in "superinsulated" homes, especially those that are "well thought out." There are also stories of ductless mini-splits working well in not-so-ideal-but-not-too-bad homes, albeit sometimes with qualifiers such as "depending on occupant expectations" or "I like cooler bedrooms at night," "wear a sweater," or "keep doors open," "people who close doors are weird", etc.

    Strategies for dealing with less-than-ideal homes include adding electric resistance heat to bedrooms (possibly with occupant sensors to assure that expensive electric heat isn't wasted on an empty room), or moving to a ducted mini-split.

    So when does point-source heat become insufficient? This pair of articles provides the most concrete, quantitative answer to that question:

    Here are some other useful comments to reader questions:
    See comment 3 in:
    .. or comment 4 in:

    If you just want to reduce energy bills with little fuss, it would seem that keeping your electric baseboard heaters would allow you to install a couple of efficient single-head ductless mini-splits to carry most of the load, with the electric heaters satisfying comfort issues in distant, high-load rooms.

    There was an extensive field study in the Northwest that evaluated the performance of mini-splits. Most of the homes in this study kept their electric baseboard heat, and they just dropped a mini-split or two into place. Savings were variable based on occupant behaviour and house configuration, but I think the average savings was around 40%:

  12. Expert Member
    Dana Dorsett | | #12

    I have multilple relatives living in sub-code housing heating with mini-splits and are glad to have them, and have yet to see expensive mainenance issues 3+ years into it. It's not at technology merely for the super-insulated, nor are they all maintenance nightmares if properly installed.

    The NEEA in-situ studies were well documented and convincing. The fact that the Eastern Idaho cluster of 12 one-ton Mitsubishi MSZ-FE12NA had a fleet seasonal average COP of about 3.0 in a US climate zone 6B climate zone location (Idaho Falls) gives me confidence that the even more efficient FH versions will beat that handily in a somewhat warmer (if wetter) zone 5A climate like eastern MA.

    I'm more than dubious about PTHP solutions paying back "...near a decade beforea mini split" in an eastern MA climate. They're pretty cheap to install, but the low-temp efficiency performance isn't much better than a toaster, and the retail price of wintertime power in MA is north of 20 cents/kwh in most places this year. If a mini-split with an average COP of 3 pays of in about 2.5-3 heating seasons, it it pays off nearly a decade ahead of time, does than mean a PTHP solution comes with a cash rebate worth 5 years worth of heating power use? :-)

    Not all mini-spits and not all mini-split installation contractors are the same, and there ARE ways to screw it up, and there are crummy/good/better models to select from. But it's a harder thing to screw up than a ground source heat pump.

  13. jeffshero | | #13

    Charlie, thanks so much. I am definitely going to wait until I am able to build as best of an envelope as possible at the moment (not likely to replace windows immediately but we'll air seal, weatherize and add insulation. I'm going to be putting all of my reviews on Angie's List for sure.

    Aaron, I really appreciate the info. I will be digging into it all shortly.

    Dana, I agree. All of the info that you all have provided me seems based in quite a bit of experience and research. There wasn't much substance at all to S.E.'s thoughts on PTHP. It certainly doesn't seem like it is somehow a full proof installation solution that wouldn't also suffer from a poor implementation.

    Thank you all, again and again.

  14. srenia | | #14

    Used name brands (top of the line low temp) on the mini splits and qualified installers. Still broke down and lost 7k in the first year of them being installed. In a zone a zone 5. If you have extra money they could work out for you, but its a gamble. Pthp's have a long track record and work very well. Those cost me 1k. Those also have high COP and backup heat built in. When its negative 30 out like last year your mini split just won't keep you warm.

    Take it from someone with experience or a pencil pusher. Your choice.


    Saying someone's thought don't have substance without any specific research behind it shows your lack of education. Its a sign that you lost the argument. A couple years ago I might have agreed with your statements but experience is a great teacher. . Maybe in another decade mini splits will be higher quality and work at even lower temps. Currently they are a niche product.

  15. charlie_sullivan | | #15

    This should perhaps be a new thread, but for the people who have had trouble with the problems involve leaks of refrigerant? If so, the global warming impact of installing lots of mini-splits might be as bad as coal-fueled electric heat.

  16. srenia | | #16

    Bingo in my case. The court in my case said it was under the manufacture warrantee. The manufacture said it was to the installer. In the end I loose and you are right about the leaking toxins going in the air hurting everyone.

  17. Expert Member
    Dana Dorsett | | #17

    S E: "Saying someone's thought don't have substance without any specific research behind it shows your lack of education."

    Nobody claimed a lack of substance, only a gaping chasm of difference in real-world experience. I take no joy in your miserable experience with mini-splits, but where IS the pencil-pusher's statistical evidence that your experience is typical? Educate me, by all means!

    The NEEA's ductless heat pump project involved thousands of mini-splits over a range of climate zones and over more than just a couple of years. The reliability was (and is) surprisingly high, and they went out of their way to collect those reliability & owner satisfaction data (not just energy use numbers.) That's not to say there weren't disaster installations there either. I know of one case where the mini-split didn't have the proper refrigerant charge from the get go, was mis-diagnosed and mis-repaired (at the owners expense) by a tech from the original company that installed it. That was only resolved when tested diagnosed & properly charged by a third-party technician from Ecotope, a contractor to the NEEA project. Had the owner not been part of the NEEA project he may have given up.

    But that was an outlier case, not the typical.

    I've yet to find any HSPF/COP numbers on PTHP units in the same class as mini-splits, but if you have some higher-efficiency models to recommend, I'd love to know them. I've yet to find one that has COP better than a toaster even at +15F (let alone -30F) but if they exist, let's have it! Most have COPs in the low to mid-3s @ +47F, but fall off in efficiency pretty fast below freezing, usually switching to only resistance heat at outdoor temps of 25F or lower. In locations where the binned hourly average temps in January are 25F (pretty common in zone 5) that's a pretty big efficiency hit. I've yet to see a PTHP with a COP north of 4 @ 47F, but most of the better mini-splits beat 4 @ 47F even at high speed, and deliver even higher efficiency at part load at those temperate temps. If there are some exceptional PTHP models out there to know about, please SHARE!

    I don't know of a US climate zone 5 location that actually hit -30F last winter (it certainly came nowhere near that in coastal MA). Are you somewhere in northern IL or IA maybe? The Fujitsu AOU- xxRLS2-H series units keep chugging away putting out decent heat at -30F, according to a guy in Quebec who regularly posts here. The fine print on Mitsubishi submittal sheets state they auto-stop at -18F or so and don't re-start until it warms up to -13F, but I've read internet scuttlebutt reports indicating they are still going even in the -20s, at some untested but still substantial output capacity.

  18. srenia | | #18

    lol. That's one of the models I used. Thanks for proving me right. You are complaining that pthp do not push enough cop. I agree. You have to acknowledge those extra cops do not pay for themselves on the mini split. You don't end up saving money in the long term or short term..

    I totally would have agreed with you a couple years back. Talking with different HVAC installers in my area they acknowledge the high breakdown rate of these mini split units. Its a nice niche product but isn't ready for the mainstream yet.

    Pthp are cheaper, payback quicker and do not break down as much. If they do break down its a simple 15 minute switch and you are running again. Its just a better product for the mainstream.

    To put it into numbers I would have to save 6000 dollars in order to break even on a mini split system verses a pthp. 6000 that could be spent on a solar grid tie of around 400kwh per month. That would beat the cop numbers on the mini split and then some.

  19. Expert Member
    Dana Dorsett | | #19

    In places with 25 -30 cent electricity the higher efficiency of a mini-split definitely pays for itself over & above a PTHP.

    In the parts of the upper midwest with 8 cent retail electricity, maybe not so much.

    At MA-type electricity, propane & oil pricing, the poor seasonal average COP of a PTHP has effectively ZERO cost savings against heating oil or propane. Rather than paying back quicker, they don't pay back at ALL- they're an operational cost adder!

    They're cheaper to install than mid-efficiency propane or oil, but the lifecycle of the PTHP may be less than half that of a mid-efficiency boiler, making the lifecycle financial analysis a bit more complex.

    PTHPs beat resistance electricity, but we're still talking seasonal average COPs well under 2, maybe even under 1.5. At 25 cents/kwh most mini-splits would be paid off in under 2 heating seasons on the up-front + operating cost delta with resistance electricity solutions, maybe 3 heating seasons on the deltas with PTHPs.

    I have zero direct experience with the -H version of the -xxRLS2s, but Jin Kazama (a regular poster here) heats his house in Quebec with a few of those, reporting blissful warmth at -30F. I have both first & second-party experience with the Mitsubishi -FExxNA series, which seem to hold up very well in all kinds of climates, and would expect comparable reliability out of it's -FHxxNA offspring.

    Mini-splits are not new technology, though the inverter-drive units have been around fewer than 20 years. It's not a niche product, it's a standard go-to solution in much of Asia, in countries where lifecycle cost issues are analyzed mercilessly & endlessly by consumers.

    Fourth hand internet scuttlebutt such as, "Talking with different HVAC installers in my area they acknowledge the high breakdown rate of these mini split units. " is meaningless, given that not even " area..." has been defined, let alone "...these mini split units...".

    Are we to assume that the alleged un-numerated undocumented reliability assessment of nameless contractors in unknown location as reported by a nameless blog poster is a more credible source than the published results of the NEEA's long term (and still going) study? Is it even as credible as an urban legend? Or is it the opinion of someone who had a bad experience?

    Numbers are good: L' aritmetica non e un opinione.

    To get 400 kwh/month (4800 kwh/year) out of grid tied PV in MA takes about 4kw of panel, which in MA costs $14-16K, not $6K. With the 30% federal tax subsidy and other local incentives you might get it down to $10K, but that's still more than 50% higher than $6K. In 5+ years it might hit that price point. (I'm hopeful, but not going to be holding my breath, but it's not there yet.) Yet it still wouldn't cover the annual power-use difference between a pretty-good PTHP and a pretty-good mini-split in anything but a VERY high performance building, or maybe a modest room/apt. in a large multi-story hotel/apartment building.

    It's pretty clear that at any COP the lifecycle cost of a mini-split that craps out in 3 years or less is pretty much a loser anywhere. I haven't personally encountered one of those (yet)- I believe they exist, but I don't see any evidence that it's the norm, or even within the 2-sigma tick on reliability / longevity. If the data exist, please tell us where to find them.

  20. srenia | | #20

    I hate promoting any brand on this site. Their is your grid tie solar figures. For around 6k I saved buying a PTHP I'm able to buy solar. There is more than one way to solve a problem. The same price I have more efficient system and much easier to install. Sorry to burst the mini splits are the Holy Grail of heating and cooling dogma.

    The simple data outside of most HVAC installers would be the lack of real warrantees from the mini split manufactures. These manufactures are not backing up their mini splits.

    I lean towards EPA stoves for heating needs. When using electric PTHP is the better alternative to baseboard heat. Mini splits I'm not totally against as long as its realized that it not financially better on total ownership cost, greener or more reliable.

    The bonus to PTHP is not needing a separate backup heat when it gets real cold. Not having two separate heating systems lowers cost even further. If the manufactures guaranteed their products, added back up heat and lowered the price to under a thousand installed then mini splits would be main stream.

    The issue with mini splits working at very low temps is the cops go down hence why a backup to the mini splits is required. Mini Splits need to cycle. Not only does your mini split reach near 1 cop it also shuts down periodically. Not an ideal situation unless you are in a passive house.

    The better and simpler solution is PTHP manufactures increase the low temp range of their units. I know GE uses electric and the heat pump at the same time. GE is not as reliable unfortunately.


    Disregarding me as some poster that had a bad experience to negate the conversation shows how uneducated you are. Resorting to those tactics means you already lost the argument. There are many ways to solve energy issues and I understand that. Do you?

  21. Expert Member
    Dana Dorsett | | #21

    The "up to" figures of your web-vendor example means if you install it in high-dry parts of Arizona you might hit those numbers. In the northeast or upper midwest you'll do no better than about 3/4 of their "up to" numbers, but you'll get more than half.

    You still haven't shown your math on lifecycle cost, with no information at all as to the average length of service or the per-kwh cost of grid electricity.

    The wintertime power rates in MA are volatile due to gas-grid congestion issues, and most people will be paying something in mid to high 20s of cents/kwh for residential retail power this winter. This is 3-4x what some other folks are paying in the midwest, and it dramatically effects on the lifecycle financial model. There can be no realization "...that it not financially better on total ownership cost, greener or more reliable" until/unless the necessary information is supplied.

    So again, educate me. Show me your paradigm case numbers.

    There is no "holy grail" around mini-splits, but the very low seasonal efficiency if PTHP systems in a New England climate combined with some of the highest retail electricity in the US make mini-splits more financially viable than PTHP, unless you can demonstrate a very low reliabilty rate that other seem to miss.

    Yes I totally understand that there are many ways to solve energy issues. I also understand arithmetic- show me some.

  22. srenia | | #22

    Already did and you don't accept it that mini splits are not the holy grail. Nothing more I can do but refer you to the information that I gave and hope it sinks in.

    To others reading there is no one answer. The answer are specific to your needs. The PTHP verses mini splits is already won by numbers of sold units in the US. There is reasons why people choose one over the other.

  23. Expert Member
    Dana Dorsett | | #23

    I totally accept that mini-splits are not the holy grail.

    There has been no financial analysis presented, as alleged- there isn't anything yet that could POSSIBLY "...sink in". You''ve show us SQUAT for analysis, even a straw-man analysis.

    The time period over which " I would have to save 6000 dollars in order to break even on a mini split system verses a pthp " is... ?

    The per-kwh retail electricity rate is... ?

    The annual heating degree days are... ?

    The heat load of the space being served by the heating system is presumed to be... ?

    The outside design temperature is... ?

    The presumed lifespan of the mini-split is... ?

    The presumed seasonal efficiency of a mini split is... ?

    The presumed seasonal efficiency of an PTHP is... ?

    At 2x the efficiency or better at 25 cents/kwh it doesn't take much time at all for the upfront cost delta between a PTHP and a mini-split to evaporate.

    If you have off-peak rates of 5 cents/kwh and low heat loads, it may never pay off.

    Just for yuks, let's build a straw-man case for a PTHP + solar vs. mini-split in a New England zone 5 kind of climate:

    Design heat load =10,000 BTU/hr at a design temp of 0F, 6500 heating degree day climate, presume heating/cooling balance point of 65F.

    Average seasonal efficiency of a 1-ton mini-split= 3.0 (a bit pessimistic for a zone 5 climate).

    Average efficiency of 1-ton PTHP= 1.7. (probably optimistic for a zone 5 climate)

    Mini-split installed cost of $4000 (probably middle-of the road) PTHP installed costs $600 (optimisitic, for a 1-ton), for a cost delta of $3.4K.

    Presumed lifespan of a mini-split: 15 years. (That's owballing it, but OK, say you have to say, replace a refrigerant valve in in that time frame.)

    Presumed lifespan of a PTHP: 25 years (Could happen, probably optimistic.)

    For the design load to be 10,000BTU @ 0F, if persisting for 24 hours that would be 240,000 BTU/day

    At base 65F that's 65 Heating Degree Days, which means the place needs 240,000 / 65HDD= 3692 BTU/HDD

    For a 6500 HDD season it then takes 6500 HDD x 3692 BTU / HDD = 24,000,000 BTU.

    At an average COP of 3, at 3412 BTU/kwh, the mini-split delivers 3 x 3412 BTU/kwh = 10, 236 BTU/kwh, so over the heating season it uses 24,000,000 / 10,236 = 2345 kwh.

    At an average COP of 1.7, at 3412 BTU/kwh, the PTHP delivers 1.7 x 3412 BTU/kwh = 5800 BTU/kwh. Over the heating season it uses 24,000,000/ 5800= 4138 kwh.

    Difference of power used per heating season is then 4138 - 2345 = 1793 kwh

    At 25 cents/kwh that's an annual cost delta of $488. The upfront difference is paid off in operating cost in $3400 / 488= 7 years (simple) which is well within the anticipated lifecycle of a mini-split if you use NEEA's reliablity data sets, and would even pay for the replacement unit by the time it actually croaks.

    At a nickel / kwh it's an annual cost savings of $90, which would take $3400 /$90 = 38 years, which probably something like twice the realistic lifespan.

    At the national average of 13 cents/kwh it's an annual cost savings of $233, which would take $3400/ $233 =14.5 years to pay off, which is still within the presumptive lifecycle if not by much.

    This assumes zero electricity price inflation or deflation over that 15 years.

    At an optimistic installed cost of $3.25/watt that $3400 delta would buy you an "extra" 1.046 kw of grid tied PV, which in MA would deliver about 1255 kwh/year over the first 15 years, less on the trailing years. Assuming there is a 30% tax credit, the out-of-pocket ends up at $2.28/watt, so call it 1.491kw, which would JUST about deliver that 1793 kwh/year power use delta (maybe yes, maybe no, depending on the year.)

    So, if you skew the numbers enough there is an outside chance that you can break even with a PTHP + solar than a mini-split (and in warmer sunnier climates that argument can be pretty good).

    But if you assume a COP of 3.3 for the mini-split (likely for an FH12NA or the non-H -12RLS2 ), and a COP of 1.5 for the PTHP (probably more realistic, but who really knows?), and a more realistic 2014 price of $3.75/watt ($2.63/watt after tax credit), the case goes completely to hell.

    At buck-fifty/watt solar (after subsidy) the case might be pretty good.

    I've shown you mine, let's see yours.

  24. srenia | | #24

    Already did and you don't accept it that mini splits are not the holy grail. Nothing more I can do but refer you to the information that I gave and hope it sinks in.

    To others reading there is no one answer. The answer are specific to your needs. The PTHP verses mini splits is already won by numbers of sold units in the US. There is reasons why people choose one over the other.

    So you are saying that a mini split will save 6000 over a PTHP? lol. Ok. Whatever you say. I use 6000 because I wasted 7000 on those mini splits and minus the PTHP I bought. Number crunch all you want and you'll still be wrong like I used to be.

    Funny this reminds me of the passive house verses net zero. In the end net zero wins because its more reasonable. Passive house is a good teacher though.

  25. Expert Member
    Dana Dorsett | | #25

    The information you actually gave is woefully short of being able to derive a lifecycle cost, or even an operational cost. You offered a "pencil pusher" explanation, but $7000 - $1000= $6000 cannot be the whole equation (unless you're not paying the power bill.). $/MMBTU still matters.

    Unlike the Passive House /Net-Zero argument, the case can't (yet) be made for PTHP + PV, in lieu of higher efficiency ductless. At the current installed cost of PV one can't make up the difference by installing solar, but that will happen fairly soon- before 2025, if not before 2020.. When that actually happens(as opposed to only in our dreams) it'll be a whole new ball game. When that day comes there may still be a case for mini-splits, but it won't be on purely economic grounds. The landscape of net-metering may have shifted by then, and if "demand charges" get applied to residential rates the financial aspect might still be there. We'd have to run the numbers against the reality of that day.

    Yes, in high priced electricity markets a mini-split CAN deliver well over $6000 in reduced operating costs within any reasonable lifecycle. Apparently (for reasons still not divulged), yours did not have a reasonable lifecycle. While I'm sorry to hear that, but would be very interested in the specific failure modes. Your experience is very different from mine, and very different from the published data from the NEEA ductless project.

    I'm keeping at least 2nd-hand tabs on a half-dozen FE series Mitsubishi units, the oldest of which is going into it's fifth heating season, most of which have three years behind them. The average installed cost was on the order of $3500/ton, (not the $4000 I used in the 1-ton straw-man. analysis). None have had any maintenance issues, and all are operating at the anticipated power use. The NEEA is keeping tabs on literally thousands of units, and publishing periodic updates.

    To buy your argument means I would have to heavily discount my own experience as a handful of outliers (as if I'd rolled snake eyes six time in row, even though the dice weren't loaded), and ignore the published data from the NEEA, and accept on faith that somebody using the handle S E from some unknown location who had unspecified problems with a couple Fujitsus has a better handle on it . Somehow I'm still dis-inclined to make that leap of faith, given the case as presented.

    You're absolutely right.- $7000 - $1000 = $6000. But it's meaningless without the context.

  26. Expert Member
    Dana Dorsett | | #26

    Somewhat ironic to be accused of defamation here. I've never disparaged you, nor in any way defamed you, only pointed out why I don't accept your personal assessment as an authoritative source, laying out the arithmetic of my point of view, and referring to the much larger body of work performed for the NEEA.

    On the other hand, I've been accused of "Saying someone's thought don't have substance without any specific research ", ( which is categorically false- does that mean I'm calling you a liar? :-) ) and of having a "...lack of education", and called "uneducated" multiple times, apparently for disagreeing with your assessment.

    Clearly we will never see eye to eye on this, but it would be at least possible to have a discussion if you would present your actual case. Simply disagreeing with you isn't the same as "negating" you. Anecdotal evidence is still evidence, yet you've barely shared yours, and seem to expect others to accept it as the general rule without really explaining it in even the remotest detail.

    If I'm defending anything I'm defending arithmetic & statistical methods for assessing this kind of stuff (and NOT mini-splits. )

    Regarding the "mainstream" aspect of mini-splits, quoting the executive summary on p.7 (p.8, in PDF pagination):

    "Almost all residential HVAC systems in Asia and a vast majority of systems in Europe are ductless, while only a small percentage of homes in the U.S. utilize DHP technology."

    What's mainstream depends a bit on the stream you're in, but this isn't some new untested technology.

  27. jeffshero | | #27

    A couple of quick updates:

    - We will be getting weatherization done soon. I should also be getting results of a Manual J in the next week and have had a few good discussions regarding mini-split options. I was told that we should be seeing hyper heat multi-zone split systems with single condensers up to 42,000 BTUs in New England in the next few weeks. I can give model information once I have it from the HVAC firm.

    SE, I think you may have "loosed" a few too many brain cells from the lost refrigerant from all those foolish mini splits all over the place even though you have pointed out that there are significantly less units than PTHP (without referencing of course). That is not, however, evidence of their superiority. Perhaps you could research mortgage backed securities, snake oil, or ford pintos as other things that people did not optimize their consumer and investment dollars with. You certainly have not provided any substance here and, by definition, you would need to be a known entity not an anonymous internet commenter to be defamed. I cannot be sure of your intentions, but you have failed miserably if you meant to persuade someone currently in the market against purchasing a mini split system.

    Dana, thanks again for your help. Feel free to comment as you like, but it doesn't appear that our friend SE is actually interested in rational discourse. It would be great to get something more than anecdotal evidence to understand his or her reasoning, but we may not be educated enough as he/she has indicated several times. It is probably time to disengage. I look forward to letting you and the other helpful folks know how we are proceeding.

  28. srenia | | #28

    Again using tactics of defamation to make your argument? Sorry you believe your argument is so bad that you have to resort to that. You should be a politician or a Laywer. Be a good fit for you.

    Bottom line is more units of pthp are sold In the US because of the reasons stated earlier. Pthp's are mainstream and mini splits are not. Get over it and realize its alright to be wrong. The way you defend these mini splits makes me believe you have a financial stake in mini splits....

    Like I said earlier, I prefer EPA wood stoves.

  29. srenia | | #29

    I wish the best in your endeavor using the mini splits. I'm not against them as it might seem. Just against the false premises that these are sold on. To each home situation a different heating option is needed. Having a open discussion of ideas is good. Knowledge is key. This includes personal stories, studies and alternative solutions. Dismissing any of those out right limits discussions. There is compromise in most building decisions. Its the nature of the beast.

  30. kaaset | | #30

    A company called Steffes makes off peak electric storage heaters that can be utilized in an HVAC situation along with air pump addition for extra efficiency. They are found at

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