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Community and Q&A

Do heat pumps and super insulation complement or compete with each other?

vensonata | Posted in Green Building Techniques on

After reading the article on “how much insulation is too much”, I found Marc Rosenbaum’s stats on 11 cold climate house configurations interesting. He points out that the difference in energy savings is very small between a minimally insulated and poorly air sealed house and a super insulated and very tight air sealed house. This is because he starts with an 2.5 cop heat pump and a heat pump domestic water heater. He sets the miscellaneous loads (appliances and lighting) at 4800 kwh year. The domestic hot water at 1850 kwh year, and the only variable is space heat. The bad house uses 2156 kwh year the best house (super insulated) uses 774 kwh year. Only 1382 kwh difference!
So it seems it is uneconomical to super insulate when you have a heat pump. Or…it is uneconomical to have a heat pump if you super insulate. In other words these two strategies are not friends…they eat into each others return on investment. One must choose. Which is the best choice? In new build, I go for super insulation. In old build…heat pump. Am I right?

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  1. Dana1 | | #1

    If your focus is solely on the marginal cost of space heating they compete. But they don't, really. Each has to be treated separately, and the bring different things to the table. This isn't new build vs. old, and it's not all just lifecycle energy cost, it's resilience and comfort too. They totally ARE "friends", and are almost never mutually exclusive. But trying to figure out what's "right" requires clarifying your performance goals and the rationale behind each.

    Superinsulation does remarkably little for cooling loads. As I pointed out in the discussion on that blog, even superinsulated houses need cooling in many climates- it's not either/or. There are many PassiveHouses that need cooling, and the heating output of a mini-split more than covers the heating loads of those houses, which calls into question the rationale for the 20-50% of the higher envelope performance, if were otherwise going to be heated with resistance heating. What end is it serving? Is it carbon-rational? Is it comfort-rational? The answers will be different in differing situations.

    A heat pump does not provide moisture resilience or freeze-up protection. A superinsulated building does, but the degree of super-insulation required for that end happens well before PassiveHouse, and in many situations, before Net Zero Energy.

    The lifecycle of insulation is much longer than that of a heat pump, and the lifecycle (carbon or cash) costs of each are different, and hard to calculate with certainty. The future price of energy has big error bars. But leveraged with a heat pumps that are more efficient with each generation, has a declining cost over the lifecycle of a house even if there is electricity price inflation.

    There is a pretty good case for the argument that too often passive house levels of insulation ends up going beyond lifecycle carbon-rational as well as lifecycle energy cost rational in the face of the falling carbon & financial costs of PV + heat pumps. That doesn't mean going beyond code min isn't rational on some other basis. Even if the heat pump & PV have to be replaced in 20 years, the next generation of each will be cheaper, lower-carb, and more efficient. If you can get the house to net zero energy with an array that fits on the house using today's PV & heat pumps, by replacement time you'll be able to cover the energy of your electric car too. In some cases it's financially rational to cover the automotive + house energy even today.

    Net zero energy isn't critically important in and of itself- it's more of a milestone beyond which most people would need to be clear on their performance goals. In CA beginning in 2020 it's a milestone beyond which one needs to be to get a certificate of occupancy on new construction. From strictly a financial lifecycle cost point of view, Net Zero Energy is likely to be pretty close to the sweet spot in locations where cooling needs cannot be met with nighttime ventilation strategie (or even where that strategy works.)

  2. charlie_sullivan | | #2

    Elaborating on Dana's last point of net-zero being a semi arbitrary milestone:

    If you ask why net zero as a goal, one way to describe it is as sizing the solar array at 100% of the annual usage. Then you are asking why 100%, as opposed to say 75% or 125%. Well, 125% would mean you are providing electricity to be used by others without compensation. That's a nice thing to do (and in some states you can even sign up to have it donated to your favorite local non-profit), but it might make more sense to donate money directly to your favorite non-profit, if you think they make good decisions about spending the money you give them. In any case, 125% is not cost effective with ordinary net metering scheme. What about 75%? That can make sense, if you are not getting a loan and you are cash limited, if you are space limited for an array, or if you expect your usage might decrease. But if you think you know your load, the return on investment on the last 25% will be the same as the the return on the first three 25% increments, so they make sense, a simple argument would say the last 25% makes sense too.

  3. charlie_sullivan | | #3

    On Ven's point, "it seems it is uneconomical to super insulate when you have a heat pump. is uneconomical to have a heat pump if you super insulate."

    That can be true to some extent--if I evaluated improving my envelope back when I had a 60% efficient oil boiler and heating oil was $4/gallon, the return on investment looked fabulous. But once I installed a ground-source heat pump it became much harder to justify improving the envelope based on the monetary value of energy savings.

    But if you are making both choices together, either in a retrofit project or a new build, there are ways in which super insulation and heat pumps--particularly mini-splits--play very well together. When you improve the insulation, not only do you decrease the total heat load--you also decrease the number of heat sources you need to maintain temperature uniformity. So the cost of the heat pump system goes down from both the total load and the number of sources needed. And, since heat pumps with good modern motor speed controls built in do best when they are modulating below their maximum capacity, you can more the heat pump into a more efficient operation mode when you add insulation.

  4. vensonata | | #4

    I like the consideration of reduction of the number or capacity of the heat pump as a factor of increased insulation. A single source may be possible with super insulation whereas multi head would be necessary without substantial insulation upgrades. And that might inject another variable. Should insulation be limited to easy access attics, and the remaining provided by heat pumps? Certainly the elimination of the insulation value of R7 windows vs R3 windows would favor the heat pump. So perhaps we could say low cost insulation upgrades are rational with a corresponding reduction in heat pump complexity, capacity and price. But high cost insulation is not rational if the heat pump still gives an actual return on investment.

  5. onslow | | #5

    I can't read the prime material and must guess based on the postings, but it would seem that some of the assumptions used in deriving total kwh usage are a bit suspect.

    There have been extended discussions about how air to air heat pump COPs generally fall as outside temperatures drop. Without looking it up, I would guess that a COP of 1.75 might be an acceptable to generous number to use in a truly cold climate regime. Even at 1.75 my own experience for February in cmz6 would have lowered my usage to 1550kwh for the month. If I halve the heated sf to 1500 then (if it proved linear) maybe I could hit 775kwh for one month. Mr. Rosenbaum's super insulated house must be one doozy of a house to manage an entire heating season on that.

    For perspective, I use straight resistance heat in the form of radiant cove heaters in each room. Yes the electric bills are seemingly hellish, but when divided out over the month of February my heating usage is approximately 9400 btus per hour for 3000 heated sf. I think we are well insulated. We definitely are eating efficiency lost by not using heat pumps so we may have a totally silent system. We also are unlikely to experience a system lock up or freeze up when a 20" snowfall hits. Then again when the sun goes down and the air temp is at zero the COP may not be 1.75 for 12-15 hours in Dec-Jan-Feb so maybe the efficiency hit isn't as large as might be perceived.

    The floor plan is also not mini-split friendly and would have required at least three units with additional air exchange to distribute well. The whole radiant system installed was less than one mini-split. I will grant everyone a "gotcha" for deciding on the insulation levels based on propane costs three years ago. It tanked this year, so my careful figuring doesn't look so clever now. At least I don't have a potential bomb in the yard and worries about how the propane truck will make it up our very rural roads.

  6. vensonata | | #6

    The consideration of cooling is certainly a factor with the heat pump vs insulation alone. However simple air conditioners are so cheap that if that is the only consideration then it would be unnecessarily expensive to use a heat pump for that. As to replacement costs for heat pumps and PV. I am not sure heat pumps will fall in price very much more...although probably PV will. But most PV will still be performing well in 35 years...why replace?
    I had purposely left out PV in the consideration as just the two factors of HP vs Super insulation is already surprisingly complex. If we bring in PV as the third leg of the tripod, it turns into a final exam question in 4th year engineering at MIT.

  7. vensonata | | #7

    The houses profiled by Marc Rosenbaum were hypothetically located in Concord, NH. He is very experienced with the numbers on heat pumps and I would accept his 2.5 COP as quite realistic. These 11 houses don't exist except on paper but they do have numbers that have been reproduced in real houses. It is a pity the article is available only on the non public site, since it is really very interesting and has two other designers dealing with the question of "how much insulation is too much".

  8. user-4524083 | | #8

    Ven and others - I think that while this is a good discussion, the assumptions around the data are incorrect. In the graph, " Cases - Annual Heating/ Total Energy", the first bar is case #2, a house with R-30 walls, i.e., a "Pretty good house", not a poorly insulated house. The graph shows that going from a well insulated home to a over the top insulated house ( R-60 walls), you'd be better off spending more on PV. This is not new info., just well graphed - IF you read it carefully. In the comment section of the article, we are told that case #1 used 12,400 kWh. It would have been useful to include the code minimum and Case #1 in the graph.

  9. GBA Editor
    Martin Holladay | | #9

    The calculation isn't as complicated as you make it sound. There is an incremental cost to installing minisplits compared to electric-resistance baseboard heat; you can easily calculate that incremental cost. You can estimate a lifespan for a minsiplit -- maybe 16 or 18 years. You can then determine whether the incremental cost is worth it, based on energy savings over the life of the minisplits.

    Do that with two or three insulation scenarios. Thicker insulation costs more but lowers your energy costs (as well as your energy savings if you choose the minisplit option). Look at the four or six scenarios, and pick the sweet spot.

  10. Reid Baldwin | | #10


    One thing you might have noticed if you had access to the article is that Marc assumed that half of the plug loads contribute to satisfying the space heating requirement. When you get to pretty good house levels of insulation, you are probably unintentionally doing much of your heating with electric resistance. Unfortunately, that unintentional resistance heating doesn't stop in summer.

  11. vensonata | | #11

    The case 1 house is identical to code except better windows and air sealing. The walls are only a pitiful R15. The last house, case 10, has R60 walls!! and R 90 ceiling. The savings on space heating are only 1382 kwh annually. What "distorts" this rather trivial difference is the heat pump of Cop 2.5. Without the heat pump the annual difference between code and maximum would be 3500 kwh. Still not much actually, perhaps $500 year difference. It is worth about 25x500= $12,500 total investment in insulation and windows and air sealing. Then there is no way to justify a heat pump on top of that.

  12. vensonata | | #12

    I suppose the initial slight "misdirection" is in the fact that all of the 11 houses (including code house) are already assumed to have heat pumps at 2.5 COP. The scenario should be run the other way as well with all of them with insulation alone and then show the difference in the price of heat pumps to make up the difference. At that point the PV would also suddenly stand out as a better investment. It seems the three of these energy factors when on the same building do get a little complicated.
    (The cherry on the cake is when you add enough PV to charge an EV and eliminate your gasoline bills then a new synergy changes the whole picture. But that is for another Q and A.)

  13. user-4524083 | | #13

    Ven- Your point on mini splits vs. PV is a very valid one and worthy of more consideration. But I think that you are still not reading the chart correctly. The first case in the graph is Case #2, not case #1. I think that you are taking the difference between Case#2 and Case#10 ( 8804kWh - 7421kWh = 1383kWh) and then multiplying this by the Cop of 2.5 to come up with a difference with resistance heat (and without heat pump) of 3478kWh. But the Case 1 house is not listed in the second chart. The case 1 house uses 12,400kWh, significantly more than the Case 2 house at 8804. So maybe that makes the mini split more reasonable?

  14. vensonata | | #14

    Ah, I see. Yes, you are correct, the second graph starts at house 2 with R 30 walls etc, nothing to sneeze at. Overall the picture only makes sense when we increase the size and cost of the heat pumps, while leaving the Cop 2.5 constant. There is no observation that the less well insulated house may require two heat pumps or multi head, and that skews the economic factors.

  15. GBA Editor
    Martin Holladay | | #15

    You wrote, "all of the 11 houses (including code house) are already assumed to have heat pumps at 2.5 COP. The scenario should be run the other way as well with all of them with insulation alone and then show the difference in the price of heat pumps to make up the difference."

    Yes, you've got the right idea. That's basically what I was saying. But I wouldn't run 11 insulation scenarios -- just the two or three insulation scenarios that strike me as most reasonable.

  16. Reid Baldwin | | #16

    This is a particular example of the general idea of diminishing returns. Any two actions that act by reducing the same loss will reduce one another's effectiveness.

  17. vensonata | | #17

    "Any two actions that act by reducing the same loss will reduce one another's effectiveness." Eloquently put, and worthy of Newton. Although I might add that it is their economic effectiveness that is reduced, rather than their energy or comfort effectiveness.

  18. Jon_Lawrence | | #18

    It all comes down to comfort for me. The fact that a super insulated house uses much less energy is cool too, but that is the gravy and cherry on top.

  19. Dana1 | | #19

    Charlie (#2) : Whether or not and how much a Net Positive Energy house gets remuneration for the extra export to the grid varies considerably. In some locations in the US it's at the full retail rate, in others it's at some aggregated wholesale average. Under New York's regulatory revisions it looks like it will end up being the LMP + grid costs + externalities. The LMP is the Localized Marginal Price, the spot market wholesale value of the energy at a particular location within the grid. The grid cost offsets would have to be calculated by a methodology agreed upon by various stakeholders, as would be the value of offset externalities, which would change over time (but not on a 5 minute or 1 minute basis like the LMP.)

    Only in the most egregious cases in the US is excess export actually a gift to the utility company. In cases where it turns out the house is producing 125% of the house load with low or no compensation, that can become a driver in the decision tree for buying an electric vehicle sooner rather than later.

    Ven, (re #6): The difference in installed cost between resistance heaters + window-shaker AC and a ductless mini-split heat pump can be surprisingly small, and "worth it" from a noise & comfort factor alone. To be clear it's the efficiency of future heat pumps more than the raw dollar cost reductions that delilver the lions share of the lower levelized cost of the thermal output.

  20. vensonata | | #20

    Apparently most people will be sold on efficiency through the "comfort factor" rather than civic duty. It is wise to accept that, as the means to the end of preserving the environment and social well being. The green movement requires the skills of psychology as well as heat pumps!

  21. vensonata | | #21

    As I continue to reflect on the math of PV, heat pumps and insulation one theme keeps emerging: heat pumps are a brilliant technology but they need to fall 50% in price. They don't need to get more than a 2.5 cop, but they need to get really cheap.

  22. STEPHEN SHEEHY | | #22

    Ven- Why do heat pumps need to get cheaper? Certainly ductless mini-splits are already cheaper than alternative systems. My two units cost $6500 installed (that's for both, not each). If you want or need A/C as well as heat, they would be the best alternative for a tight, low load house. Any hydronic system or hot air furnace plus duct work will cost a lot more than that.

    I think many people don't like the look, although once installed, they just blend in like every other appliance. No one ever says "I won't put a refrigerator in my kitchen because I don't like the look."

  23. Jon_Lawrence | | #23


    Ironically, where I live, most people don't understand the comfort factor. They are sold on the size factor, the more furnaces and BTU's the better. Then when I tell people I am building a PH that extremely comfortable and oh btw it uses a fraction of the heating/cooling energy of a code built house - they are blown away.

    Btw, I need to clarify my point above, especially as someone trying reduce my daily housing and transportation carbon to zero (without just walking or riding a bike). My point was that you should build for comfort first. Doing so will lead to significant energy savings. I am going to take the leap of faith that PHIUS is correct that their metrics produce a home that is both optimally comfortable and optimally insulated. We shall see.

  24. vensonata | | #24

    Stephen Sheehy,
    Heat pumps need to get cheaper for two reasons. They need to compete with natural gas at 4 cents kwh. And they need to, not just break even with electrical savings from resistance heaters, but be compellingly cheaper, so cheap that no one can afford to heat any other way. It is the simplest most likely method to significantly reduce grid energy demand quickly. It works everywhere, PV does not, and renovation upgrades just aren't going to happen on a large enough scale and short enough time frame ( 100 million houses). Heat pumps could be the silver bullet...but they need to be mandatory or too cheap not to buy.

  25. GBA Editor
    Martin Holladay | | #25

    You wrote, "Heat pumps need to get cheaper for two reasons. They need to compete with natural gas at 4 cents kwh."

    I'm confused. Are you talking about equipment costs or energy costs?

    If you are talking about equipment costs, a pair of ductless minisplits is already cheaper than a natural gas furnace -- and the minisplits also provide air conditioning, something that a furnace can't do.

    If you are talking about energy costs, and if your benchmark is beating natural gas providing heat at 4 cents a kWh, then a heat pump with a COP of 2.5 beats the natural gas anywhere that electricity costs less than 10 cents per kWh. But you can't really blame heat pump manufacturers for energy costs. These energy costs vary from region to region, and they are what they are.

  26. STEPHEN SHEEHY | | #26

    To add to Martin's comment, not everyone has access to natural gas. No one near me does, for example.
    Moreover, natural gas has historically varied a lot in price. Electric rates are typically more stable. So 4 cents/kwh may not be a realistic price to plan on.
    I just had an oil furnace installed in my old house for $5400. That's just switching new for old. No ductwork or chimney or wiring. A whole new system would be far more than my two minisplits and I'd still have no A/C. No combustion in the house is also a benefit.
    Even if NG at 4 cents had been an option, I wouldn't have considered it for the new house. Of course PV runs the minisplits.

  27. Dana1 | | #27

    "heat pumps are a brilliant technology but they need to fall 50% in price. They don't need to get more than a 2.5 cop, but they need to get really cheap."

    The inherent contradiction in this statement is that doubling the efficiency is could be compared to falling 50% in price, but it doesn't need to double in efficiency to still beat the lifecycle cost of alternatives, since they don't cost as much as gas-burners to install. Even an 82% efficiency wall-furnace can have a higher installed cost than a mini-split, as well as a comparable or higher operating cost.

    Ten years ago a pretty-good 1-ton mini-split had an HSPF of about 8.5-10, and had an installed cost higher than a 2016 version a pretty good 1-ton mini-split that tests in the 12.5-14. That's about a ~50% increase in efficiency in a decade, with a modest installed-price drop even without correcting for inflation. (Even mini-ducted 1-tons are in the HSPF 10-11.5 range now.)

    That's halfway there, well within the anticipated lifecycle of the equipment.

    The biggest issue with the market is lack of familiarity by the customer base, not the upfront or marginal costs. Most people believe their loads are MUCH higher than they actually are, and the lack of familiarity with mini-split capacities & efficiency keeps them buying the same oversized solutions. Poor low-temp capacity & efficiency of ducted heat pumps of prior decades also keeps people from going with anything that says "heat pump" in the description, warranted or not. But as more mini-splits are installed customer familiarity grows and installers become more familiar and competitive in the pricing/proposals. This market hurdle can be cleared.

    If Martin's 10 cents/kwh is the magic number to clear the levelized cost of rooftop PV will be under 10 cents within a decade. From the rooftop owner's point of view already is that cheap in most places places that have SREC subsidy plus federal & state tax credit subsidy.

    At utility scale PV is already under 10 cents/kwh even without subsidy, except maybe north of the arctic circle (where it would be competing against even more expensive diesel fired generation anyway.) As more near-zero marginal cost PV and wind come onto the grid it suppresses the LMP, and with it the wholesale cost of electricity across the board. It doesn't have to have a levelized cost lower than a legacy hydro dam or already paid-off coal plant to have this effect on the electricity markets. Within the lifecycle of a PV array or a mini-split electricity pricing SHOULD become more deflationary, except where regulators opt to protect the revenues of monopoly utilities to recover sunk costs of stranded assets rather than serving the interests of ratepayers. The transition to a distributed generation model is going to be messier in some states than others.

    Natural gas is currently trading near historical record lows, and has almost nowhere to go but up over the intermediate & long term. Within the lifecycle of a mini-split there is a strong likelhood that the externalities of natural gas will begin to be priced into the product. Even on an all gas-fired grid dominated by 50% efficiency gas fired generators, at a COP of 2.5 (=HSPF 8.5) a mini-split would be operating at 125% efficiency, fuel-to-load, with marginally lower externality surcharge costs per MMBTU than a 95% condensing gas burner. Many/most US local grids are already lower-carb than a combined cycle gas plant, and will be even more so when PV is a double-digit percentage of the annual grid power generated.

    In much of New England mini-splits are already at or nearing operating cost parity with condensing gas, and significantly lower carb than condensing gas even with the standard grid-mix, and can be effectively zero carb where it's possible to buy zero-carbon power directly from generators or through brokers.

  28. vensonata | | #28

    Heat pumps only come in even with natural gas where the price of electricity is 10cents kwh or below. Which is almost nowhere. And breaking even is not persuasive enough. They have to appeal to people who don't think about these things very much, if at all. It is similar to electric cars, it is not enough to come out even at the end of 7 years with a gas car. The upfront costs are what people, unfortunately, look at. And even if we do get everyone on heat pumps we still need to purify the source of fossil fuels. But as with EV's we need to start somewhere and that is at the consumer end, radically efficient electric.

  29. vensonata | | #29

    D Dorsett,
    Why I abandon higher COP is that it can become a red herring. It is the wrong place to squeeze. Heat pumps are good enough but the price fall will be significant if the market increases. And the market will increase when they are too cheap to ignore. See what is happening with PV and wind. Too cheap to ignore now.

  30. GBA Editor
    Martin Holladay | | #30

    You sound like you are sticking to your argument regardless of what others are pointing out, which is fine. I get what you are saying -- natural gas is cheap. There are very few places where electricity is a cheaper fuel than natural gas.

    That said, some of your statements are odd. You wrote, "And breaking even is not persuasive enough. ... The upfront costs are what people, unfortunately, look at."

    What several commenters have tried to point out is that for a new house, two ductless minisplits represent a very low upfront cost -- lower than the price of a natural gas furnace. And the minisplits provide cooling. So if rational people are looking at upfront costs, they would choose the minisplits.

  31. Reid Baldwin | | #31

    I think the people that need to get convinced about mini-splits are HVAC contractors and builders. The majority of new home buyers look to these people to know what options are even available. If I had selected mini-splits, I would have had an uphill battle convincing them to install them. I cannot imagine them actually suggesting it to someone who asks their opinion. Are HVAC contractors in cooling dominated climates on board with mini-splits? That would be an easier sell than here in Michigan. How does the profit margin of installing a couple of ducted mini-splits compare to the profit margin of installing a gas furnace, central AC, and associated duct work?

  32. user-626934 | | #32

    Ven - heat pump / AC manufacturing is a mature market with plenty of competition among manufacturers as well as installers. There are something like 72 million U.S. households with a central (ducted) heat pump or cooling-only air conditioner with probably 3 to 4 million change-outs (equipment replacement) happening every year. Don't expect prices to fall.

  33. Dana1 | | #33

    From retrofits in sub-code-min houses to current code min and deep energy retrofits recent experience would indicate ductless as the lowest cost option. Even when using a tank-type gas HW heater as the heating system with window-shakers for AC mini-splits are cost competitive on both upfront cost & lifecycle operating cost. In new construction ductless typically beats a ducted condensing gas-burner with a 1.5-3 ton cooling coil & condenser by 30-50%, and hydronic gas burners by more.

    My money is on incremental improvements on mini-split efficiency & low temp capacity continuing to improve more rapidly than up-front cost. Rather than efficiency, the up-front cost is already "...good enough..." since it's cheaper than the alternatives. But when HSPFs start hitting15-16 moving in on 18 (like a best in class ground source heat pump) it becomes a real game changer, since it would also beat condensing gas on marginal operating cost by quite a bit, even at the current historical low gas pricing. Right now the marginal cost is at rough parity with gas in markets such as New England, which has both high electricity and high gas prices. It doesn't take much improvement in efficiency to make that true pretty much everywhere.

    Since the roughly half the installed cost of mini-splits is the installation, not the hardware, even if the hardware came down by 50% (not likely) the installed cost could only fall by ~25%. Another 25% improvement in efficiency won't come overnight, but it's a much more likely scenario, and would have a much larger impact on the lifecycle cost. The equipment cost is well under half the total lifecycle cost.

  34. iLikeDirt | | #34

    We are already at the point where in many cases it makes sense to spend a marginal dollar on more PV to generate more kWh rather than more insulation to save more kWh. I think Ven is saying that the same economic logic applies to heat pumps too: it might make more sense to add more PV to offset the comparative inefficiency of cheaper, less efficient equipment (e.g. electric resistance and/or window air conditioners) rather than to spend that money on a more efficient heat pump, especially because heat pumps are only getting marginally better on the efficiency front and not at all for cost, whereas solar PV is becoming both cheaper and more efficient. The lifecycle and maintenance costs of PV are much better, too.

    The efficiency improvements of heat pumps are subject to the same law of diminishing returns as insulation; HSPF 13 -> HSPF 15 is nowhere near as vast an improvement as $4/watt PV -> $3.50/watt PV. We are probably closer to the natural lower limit for how much energy a heat pump must use than the natural lower limit for the installed price of solar PV, which international experience shows us can easily fall another 50% or more. In order for a heat pump to "compete" with 50% as expensive PV, it would need to itself fall 50% in price or double in efficiency.

    This is a choice I face myself. My gas furnace is 19 years old and the terrible ductwork is in the attic. It is the last gas appliance in the house. I plan to install enough solar PV to get to net zero. Given that there will be a PV array, should I make it a bit bigger and use window heat pumps for space conditioning, with a backup pellet stove or something, or make it a bit smaller and have a much more expensive ducted mini-split heat pump installed? The former choice is more appealing for several reasons: nobody where I live has ever heard of ducted mini-split heat pumps; the equipment is simpler, much cheaper to install, more DIY-friendly, and more easily replaceable; you get per-room zoning for free; you're generating more electricity that can be used for other things or sold back to the grid during mild times of year; a wood or pellet stove would be a positive pleasure in the winter.

    For new construction below zone 5, I think there is a fairly significant chance that the winning combination will wind up being more PV + HVAC equipment that is cheaper to install but more expensive to run. The lifecycle costs with professionally-installed split heat pump units are just horrendous. They are expensive to install, expensive to service, expensive to replace… the only thing that's cheap is running them, which barely matters if you have enough PV.

    There's even an older GBA article on this subject:

  35. vensonata | | #35

    Yes, I notice the advertised prices for heat pumps can be under $1000, and mysteriously the final install price ends up $4000. Same for PV. Full system hardware $1.25, installed $3.50. So indeed most of the fat is in labor and permits. Note Australia PV fully installed is in the $1.50 watt range. Have we got the same bloated situation for heat pumps? As far as Cop goes, sure, if they can improve it without a price gain fine, why not? But it is like insulation...above COP 2 the law of diminishing returns begins to apply in a serious way.

  36. vensonata | | #36

    The people who quote installed prices for heat pumps sound like they are at parity with oil and gas furnaces, but decided on a long term vision which they felt was cleaner. But $6500 for heat pumps makes people think "what do resistance baseboards cost?" And they are really cheap. Then if they are a little numerate they start comparing savings over say, 5-10 years. Savings end up not much, if any. Only in places where electricity is 20cents kwh or above does it begin to be compelling in favor of heat pump vs resistance. I suggested to Dana that the price reduction might need to be found in the install and permits, as it is with PV.
    This phase of natural gas at ridiculously low prices will pass, however there is an urgency to the carbon time frame and if people purchase a gas furnace and prices for gas go up, they will just stay with it and grumble.

  37. user-626934 | | #37

    The small (9k) top-of-the-line performance ductless mini-splits (13-14HSPF) go for about $1,600 online. Add in a traditional thermostat, refrigerant lineset, indoor/outdoor wiring, electrical disconnect box, outdoor unit wall bracket and condensate piping, and the online price gets pretty close to $2,000. An installed price of $4,000 is pretty reasonable in my book for a quality installation.

  38. vensonata | | #38

    $2000 for installation...hmmm, I don't think that is reasonable. Maybe, like PV, they need increase their ease of installation. That is where the fat is. I must do more research on this.

  39. iLikeDirt | | #39

    $4,000 is a lot of money. Multiply this by the number of units the house will need (few can get by with only one one ductless mini-split) and the cost spirals away. But really, the low-cost heat pumps Ven is envisioning are already here: they're called PTHPs, and there are even reverse-cycle window units. Compare that installed price of $4,000 for a ductless mini-split to an installed price of a PTHP or even a window reverse-cycle heat pump. You can get reverse-cycle window units for like $400 and install it yourself, and a PTHP + professional installation shouldn't run more than $2,000. These kinds of units won't work in the frigid north, of course, but as is frequently pointed out, a ton of people don't live in the frigid north, and they should financially destroy professionally-installed split units in the bottom half of the country where it gets hot and sunny, inducing heavily populated places like California, Texas, The South, the Phoenix and Vegas metro areas, and probably even in Oregon and Washington. There are more than 140 million people living in these places.

    And consider how the PTHP and window unit are user-replaceable when they croak for just the price of the new unit. $4,000 to replace each heat pump every 15-20 years is a lot of money, especially because the labor component will rise, not fall. Today's $4,000 will be tomorrow's $5,000.

    These units are definitely not as advanced as today's Japanese mini-splits, and their technology is a bit old. But that's easy to change--a lot easier than somehow making it cheaper to have split systems professionally installed and re-installed. Labor rates don't fall in industrialized countries unless something's really wrong.

  40. iLikeDirt | | #40

    Just off the top of my head, here are some things that would help:
    - 110v wall receptacle plug-in electrical connection instead of a hardwired dedicated 220v circuit
    - No need to interact with refrigerants; linesets are pre-charged, pre-purged, attachable without tools; simplified no-lineset installation for cases where you can mount the outdoor unit right on the other side of the wall from the indoor one, etc.
    - More deployment and familiarity among "normal people"; a lot of contractors gouge on these because they're seen as luxury items for people who can afford to pay lots of money to "have the best"; $2,000 to install a ductless mini-split is a ridiculous amount of money. That's like, what, more than $200 an hour for labor?
    - Lighter weight units
    - Lower prices on the units themselves

  41. vensonata | | #41

    I think we are on to something. I have looked at a few heat pump review websites and virtually all of them cost more for the install than the hardware...considerably more. To make them really go mass scale that seems to be the area to focus on. They are in the same boat as PV. See Australia and Germany, they have figured out the install game.

  42. Expert Member
    Dana Dorsett | | #42

    In my area five years ago the all-in installed cost of better class mini-splits were running about $3800-4000/ton to have installed, all-in. Since then quotes and proposals from hack installers have been all over the place, but in competitive bidding it's now running about $3500/ton.

    About three years ago on one project it came in under $3000 / ton for three 1.5 ton Mitsubishi FE18s all installed on the same building, with multiple bids in the same range. During the same calendar year a relative on the other side of the country had a 1-off FE18 installed at her place for about $3700.

    So yes, $4000 is INDEED a lot to spend on a 3/4 ton mini-split, but that's likely an issue with the competitiveness of the local market.

    Permitting costs for mini-splits have never been an issue the way it is with PV, and don't cost any more than getting permits for electric baseboard or gas-fired heating. In most place it's really quite cheap- in the 10s of dollars, not 100s.

    Australian & German PV is cheap primarily due to the much lower soft costs of projects in those countries. In those countries the basic inspection and permitting regimes are universal nationwide, and the industry got to be very competitive quickly due to (arguably WAY overgenerous) feed in tariffs. In the US the connection standards vary by state county, utility and municipality, with a lot of time delay for jumping through hoops, adding quite a lot to the cost of installing residential PV. The cases covered in the D.O.E.'s first podcast are unfortunately not rare:

    Harmonizing connection standards and cutting red tape would go a long way toward getting US residential PV costs into the same range, but where utilities and merchant generators have a vested interest in constraining the roll out of cheap PV the still have significant power to slow the rise of the tsunami, but it's unlikely that they will stop it completely- it's only a delay.

    Still, an unduly large slice of the $3.50 for that watt of PV falls under "customer acquisition", which includes all the marketing & sales hand-holding, submitting bids, etc., which is a reflection of an immature market. When it's a commodity that the customer base already understands, as it is in Germany & Australia, that slice of the pie gets a lot thinner too.

  43. STEPHEN SHEEHY | | #43

    I can only speak to my own experience. I didn't pay $4000 each. I paid about $3250 each for the latest model Fujitsu RLS3 units. You can't seriously compare noisy window units with these minisplits.
    I guess maybe when Walmart gets into the business they'll be cheaper, but I still think $6500 total for a highly efficient heating and cooling system is pretty reasonable. There needs to be some profit built into the cost. Lower cost would be nice.
    When considering cost, remember that the cost includes something for potential warranty claims.
    I agree with the idea that spending money on the building envelope makes the most sense, as the benefits are permanent and won't require repair or replacement. For a new house, a good HVAC system and a tight, well insulated envelope are both essential. Threre are plenty of opportunities to cut costs elsewhere.

  44. Expert Member
    MALCOLM TAYLOR | | #44

    You wrote: "There are plenty of opportunities to cut costs elsewhere".

    That isn't always the case. It may be when considering high-end custom builds, but take the kind of houses I usually design. They are modest in size, don't include the usual things brought up as expendable, like granite counters or elaborate fixtures and finishes and come in around $150/ft. I'm not sure there is as much of this often cited "fat" in most construction budgets as people assume.

  45. STEPHEN SHEEHY | | #45

    Malcolm: I guess there is a lot less "fat" in such houses, but scrimping on energy efficiency and comfort seems like a false economy to me. I think a lot of people looking at hiring a designer or builder look at square footage first.

    You deal with the reality of the market, I don't, so I'll defer to you. Clearly, some combination of buyer education and better codes will be necessary if we want better houses.

  46. Reid Baldwin | | #46

    I think my question at #32 got lost in the debate. What is the contractor profit for installing 2-3 ducted mini-splits relative to the profit margin for installing a gas furnace, central AC, and associated ductwork? If it is profitable for contractors, we should be seeing contractors actively pushing these.

  47. Expert Member
    Dana Dorsett | | #47

    Ductless mini-splits are WAY more profitable than ducted systems if you can charge $5K/ton for them (I've seen quotes that high, but those weren't the winning bids) and oversize the systems to boot (seen that too.)

    Contractor profit is always relative to how competitive the local market is. Margins are more predictable for the contractor when they are working with something they are familiar, which means they can bid it tighter to the wire and still stay in business when markets are hungry. Just about every heating contractor is comfortable with bidding ducted systems, and mini-split heat pumps are something of a specially item in heating dominated parts of the US, which is why it takes a concerted educational effort on mini-split manufacturer's part to develop those markets. The NEEA utility consortium in the Pacific Northwest has done a LOT for promoting the technology there, but in most of the country it's up to the manufacturers to develop the market, which requires at least as much contractor training as customer education.

    It's not profit margin that's driving this, it's the fear of call-backs, and how much that might cost. Installers who put in dozens or even 100s per year and make it their bread & butter business are very competitive compared those who do just a handful.

    In short, you can't really blame it on HVAC contractor greed so much as contractor ignorance & anxiety. With HVAC just as with most things, words to live by:

    Never ascribe malice to that which could be explained by incompetence.

  48. vensonata | | #48

    You are treasure trove of info on heat pumps. So it is install pricing where the fat resides! And the trimming process appears to be in simplifying the unit design for ease of install ( could it be a 2 hour job?) and reliability of the equipment so no service calls. Note as a parallel situation the Tesla powerwall. The version 2 has been redesigned to simplify and speed the install for precisely the same reasons as need to be applied to the heat pump. (By the way the fully installed cost for both are rather close at about $3500.)

  49. Expert Member
    MALCOLM TAYLOR | | #49

    You are quite right, it is a false economy. I'm just not sure the answers, for builders anyway, are very simple. Even the "frills" that at first glance look easy to cut. Once these things become an expected part of a new house their absence needs to be somehow compensated for, and at present a heat pump doesn't do it for most buyers.

  50. woodreader | | #50

    Maybe some help is on the way if more products like this start to become available. Lot of good points and hope to hear on how the humidity is working out in the south east with these mini split.

  51. iLikeDirt | | #51

    That Mr. Cool unit is an excellent example of the kind of innovation that's sorely needed on the cost front, even if it doesn't go quite far enough. They could have 7" pre-charged linseeds in addition to 26' ones to facilitate straight-through-the-wall installation, and other different lengths, too. And it looks like it still needs to be hardwired through the outdoor unit; there's no reason for this since it's 110v; the power cord could easily come out of the indoor unit instead and terminate in a standard standard 110v wall plug. And at this price point, you're going to want to put one in each bedroom, so smaller output options are needed. Finally, $1,000 is still a lot of money compared to a reverse cycle window unit, and it's not that more efficient. If I can get a self-contained air conditioner for $150, I should be able to get a decent DIY-able bedroom-sized ductless mini-split for no more than about $500. Definitely a huuuge step in the right direction. With a few years of innovation and a lower price, these sort of things become a no-brainer; just throw one in every room and you're done.

    I'm sorely tempted to buy four and abandon my aging furnace with its terrible attic ductwork. At $500 each for 6000 BTU units I'd be pulling out the credit card right now, regardless of my nitpicks.

  52. user-5946022 | | #52

    Lots of discussion on cost and efficiency, but even if you solve those, you need to solve the aesthetics and the air distribution issues on ductless mini-splits.

    Aesthetics: You just cannot install today's ductless mini splits in a high end house living room. And if you try to disguise them, such as behind a soffit or grill, they supposedly don't work as well.

    Air distribution: If you build a very tight, well insulated house, you may need only 1 ductless mini split per level. Now you have the problem of one point of air distribution, with which you cannot get proper comfort.

    A poster on another GBA thread a while back wrote the solution is to assign the Apple community to design the mini split heads. While that would be great, how about micro splits? Units about the size of one or two standard supply air registers, that install recessed in an interior wall or ceiling or floor, covered by and accessed through a traditional looking supply air register. That would go a long way to solving the aesthetics. If they truly were micro - like provide 0.25/ton each, you could put one in each room, which would solve the air distribution issue. They could all connect to the same exterior compressor, and you would only need a refrigerant line between each. They would be really small, so really light, which would make them easier to install.

    Then with the savings, install one of those tube ducted HRV/ERV's, with a tube going to each room...

    By the way, does anyone have a link to a matrix that compares ductless mini split, to PTHP, to ducted minisplit, to standard forced air heat pump, to standard splits system with gas heat/electric cooling, etc. to encompass all standard residential systems? It would be a very useful educational tool.

    And if we are talking about the relative economic advantages of greater efficiency mini-splits vs more PV capacity, why not bring that conversation back around to standard forced air heat pumps? They are not as efficient as mini splits, but if you have the capacity on the PV array, that impact is less...

  53. STEPHEN SHEEHY | | #53

    CL- I take issue with your point that a single mini-split won't provide adequate heat distribution. Mine does. Once you have a tight envelope, and the space gets up to the desired temperature, the temp really doesn't change much at all with changes to the outside temperature. Most of the heating season I set my living room mini-split at 70 F. I usually don't bother turning on the unit in the bedroom. With the bedroom door open, the temps in the two rooms differ by a half degree or less. The total conditioned space is about 1650 square feet.

    As far as your comment that "You just cannot install today's ductless mini splits in a high end house living room," I guess what constitutes high end is open to debate, but once they are installed for a while, they are less noticeable than most appliances we install in high end kitchens, for example.

  54. GBA Editor
    Martin Holladay | | #54

    You wrote, "You just cannot install today's ductless mini splits in a high end house living room."

    I agree with Stephen on this one. Back in 1860, when cast-iron wood-fired cookstoves were introduced, there were two kinds of architects. The aesthetes said, "Cooks will always prefer an open hearth. No one is going to want to look at a cast-iron cookstove in their kitchen."

    The practical ones said, "Wow! This new appliance works great! I love it."

  55. Dana1 | | #55

    There are mini-splits in ultra-deluxe housing all over Asia & Latin America- it really is a matter of what you're used to.

    How pretty are hydronic baseboards or radiators, both common features of high end houses in Europe & North America?

    In Korea, in addition to mini-splits, wall-furnace type HVAC appliances can be found as the primary systems in many nice houses & offices.

    Ceiling cassettes and mini-ducted systems are options for those who can't handle anything like a wall coil or floor unit protruding from the wall.

    Ducted 1&2 speed heat pumps are usually more expensive to install than mini-splits of similar capacity. That's a pretty lousy "standard" of comparison even if they were as efficient or comfortable. It's a struggle to find gas furnace + cooling coil systems appropriately sized for a 2000' code-min house, let alone a better-than-code Net Zero-ish type of house. Sure, you could do it, but why? Modulating ducted systems are even more expensive and bench test at comparable HSPF/SEER, but typically have less modulation range. (In competing proposals on a project last fall a 2 zone dampered Carrier GreenSpeed quote came in at nearly 3x the up-front cost of the 6 zone multi-split solution that was eventually installed.)

    PTHPs can be reasonable in zones 4 or lower, but are pretty crappy solutions for high-R houses in zones 5 & higher where mid-winter binned temperature averages are in the low 20s or lower, making them barely more efficient than resistance heating for the bulk of the heating season. They are cheaper to install than electric baseboard + window-shakers though.

  56. vensonata | | #56

    This Q and A started with the question of the balance between heat pumps and insulation...or if there is one. And for me it ends more with a realization that heat pumps could cost half as much as they do simply because the installation prices are excessive.(Some easier installation design needs to be developed and appears to be possible already). If a high efficiency mini split can be fully installed for $2000 rather than $4000...well that changes everything. And why it is important on a large scale is that neither super insulation nor rooftop PV have the universal suitability that heat pumps do. There are few house that cannot use them, many that will not or cannot use renovation insulation or PV.

  57. iLikeDirt | | #57

    They're already here:

    Less than $1,000 per unit in materials costs, and DIY-installable--no refrigerant experience needed. Hiring out the install shouldn't cost more than a few hundred bucks since it's almost entirely unskilled labor.

    The unit itself is nothing to write home about in terms of efficiency compared to Mitsubishi and Fujitsu's high-end offerings, and it's way oversized for bedrooms. But that's the future, right there. DIY installable = low-cost pro-installable, too, which makes units like this feasible to just throw in every bedroom for new builds or renovations

  58. vensonata | | #58

    I agree. But I also don't see why the high efficiency Mr Slim could not be DIY or less than $500 for hired install. They are about $1600 raw. Their standard fully installed price is $3800! That is a mysterious $2200 installation fee. It needs psychiatric care.

  59. iLikeDirt | | #59

    Another promising example:

    9kBTU for $700. I understand that this is not a high-end brand or unit, but the price is right, it's not super oversized with a reasonable turn-down ratio, and if it were DIY installable and had a standard household wall plug, it would be pretty much perfect. I think a huge amount of the "fat" comes from the fact that you need licensed electrician's skills to hardwire a 220v line (likely involving electrical panel work, running conduit, purchasing expensive wiring, etc.) and refrigeration tech's skills to purge, charge, and connect the linesets. These are expensive skilled trades that involve strict government licensure, so the customer is paying for all the costs and exclusivity baked into that.

    When a unit is designed so that you can plug it into a wall receptacle and don't have to fool with refrigerants (like the Mr. Cool unit), then unskilled laborers or homeowners can (legally!) install it themselves for low or no cost, which puts substantial competitive pressure on HVAC techs to price their professional installations more competitively. Then the units become more like consumer appliances, which puts even more competitive cost pressure on them. Once they're cheap enough, you just install them yourself where you want and replace them yourself if they break, just like you do with window AC units.

    Consider that reverse-cycle window heat pumps are becoming inexpensive and widely available:

    If a basic version of this tech can make it into a packaged $500 110v unit that is user-installable, there's little reason why it can't be in a similarly user-installable but higher-end split system version for $700. Even cooler would be a built-in HRV/fresh-air feature (why not? It goes through the wall). Once we're there, that's your inexpensive, flexible whole-house HVAC solution.

    My basic point is that there no real reason why a basic version of this tech should cost $3,000 per head instead of closer to a ceiling of $1,000. For 3 or 4 units, that's the difference between a financial no-brainer and more expensive than a central ducted system.

  60. Expert Member
    Dana Dorsett | | #60

    There are many inexpensive pretty-good Chinese mini-splits with pre-charged linesets out there. Few have a rated heating capacity below +15F, most use sub- components sourced from even lower cost southeast Asian countries rather than first-tier Chinese manufacturers. These are very popular solutions in lower income countries despite some of their shortcomings, and I'm sure it's a reasonable solution for some people in the US as well, but results will vary.

    Reliability and US product support is spotty (or non existent) compared to the large Japanese vendors that have better quality control better control over their supply chains, and local distributors to support the product should it crap out in the dead of winter. It's usually possible to do a 90% DIY installation of a better class mini-split and still meet warranty requirements if the final inspection & commissioning is done by a qualified tech, which is typically the cost of a service call.

    A pretty good Daikin/Fujitsu/Mitsubishi should last 15-25 years with modest maintenance & repair costs. I doubt that a $500 low end mini-split would make it even a decade, though there may be some exceptions to that prove that rule. Any way you slice it two or three Yugos were never worth one Tercel, even if you put really nice radios in them. But Yugo sure beat a goat-cart, at least while it lasted.

  61. iLikeDirt | | #61

    I notice that the best 110v mini-splits I can find have a lower top efficiency than the best 220v models. Fujitsu's own 110v high-wall unit only hits SEER 16 and HSPF 9, compared to 33 and 14.2 for their highest end unit. You get similar numbers for the 110v units from Friedrich (SEER 17.8), Mr. Cool (SEER 17.5, HSPF 8.8), and AmericAire (a bit better at SEER 20). Is this a technological/electrical limitation of some sort, or simple a cost-cutting move to keep down the price on these units? Or both?

  62. Expert Member
    Dana Dorsett | | #62

    Taking a hypothetical example:

    A 1-ton Mr. Cool sport an HSPF of 8.8, compared to a 1-ton Fujitsu RLS3's HSPF 14.0. That means Mr.Cool uses (14.0 / 8.8 =) 1.59 x as much power to deliver the same amount of heat as the RLS3.

    Assume running the Fujitsu costs $500/year for heat, and lasts 15 years. That's $7500 in lifecycle power use.

    Running Mr. Cool would cost 1.59 x $7500= $11,927, a difference in marginal cost more than the installed cost of the Fujitsu (even if you assumed it cost $4K, which is more than what it actually costs in my neighborhood).

    And the odds are pretty high that you would be well into the second Mr. Cool, possibly working on your third by the end of 15 years.

    If you really wanted to you could go all accountant-economist and run a net present value on it using different discount rates and energy price inflation/deflation adjustments, etc, but is it really necessary?

    And is $500/year power use for heating the "right" number?

    At the national average of $0.1258 /kwh that $500/year is 3975 kwh. At an HSPF of 14.0 that would be (14 x 3975 kwh =) 55.6 MMBTU, or 556 therms, which is lower than a typical code-min new house in a zone 4 or higher location. It might not as low as a Net Zero house but close. It takes a ~3kw - 3.5kw PV array to deliver that much annual energy in a New England location.

    In a code-min house the lifecycle energy cost difference would be even higher than in the example, and at higher electricity prices the lifecycle cost difference would be higher.

  63. iLikeDirt | | #63

    556 therms is below average for code min? Wow. This past winter in zone 5B, my 1,300 square foot house used 197 therms for heating and it isn't even that great (uninsulated slab, R-14 walls, R-50 attic with ductwork, U-0.26 windows).

    At 209 therms, the Fujitsu costs $179/year for heating, compared to the Mr. Cool at $284 for a yearly difference of $105. Multiplied by 15 years means the Mr. Cool costs an additional $1,586 over the units service lives (assume equal longevity). If you install the Mr. Cool unit yourself for $1000 vs have the Fujitsu professionally installed for $3,000 (apparently a bargain for the highest-end mini-split available) then the Mr Cool unit is still ahead by more than $400 after those 15 years.

    It's actually an even better deal since less of your money is put into the house at installation time, leaving you with more liquidity. So what do you do with that extra money? If we're in rational-financial-mazimizer mode, then we have a few options:

    Option 1: Invest the $2,000 difference in your investment portfolio, which at 4% withdrawal will make you an additional $80 per year, reducing the yearly cost savings in the Fujitsu's favor to only $25--a break-even point of way-beyond-the-service-life 80 years ($2,000 installed cost difference / $25/year savings). And of course your investments are still there after the Mr. Cool unit needs to be replaced; every replacement cycle is associated with a $2,000 increase in your liquid net worth if you choose the Mr. Cool and invest the difference.

    Option 2: Use the $2,000 to buy more PV. At $4/watt you'll have 500 more watts, which in my neck of the woods is good for an additional 891 kWh yearly, according to PVWatts. That's slightly more than the additional 834 kWh that the Mr Cool uses yearly. And then if you need to replace the unit in 15 years, the additional PV is still there, so you can take option 1 and pad your investment portfolio.

    Option 3: if you're the builder, pocket the difference and increase your profit! The $2,000 per head cost difference between the two units is not going to increase the sale price of the house by the same amount. Maybe not by any amount at all, with many markets and buyers.

    So basically it seems like the more expensive, higher-efficiency heat pump is only a better deal if it lasts substantially longer, the house is an energy pig, you live in a cloudy area, and electricity prices are above average. That may describe the American northeast, but as is frequently pointed out, only a fraction of the USA (let alone the world) lives in a climate like that. The farther you get away from these conditions, the more financial sense it makes to spend much less money on a cheaper, more easily-installable heat pump and put the difference in installed costs into PV, your investment portfolio, or your profit margin.

    This also implies that PV at $4 a watt installed is a better "investment" than an actual investment portfolio in a very sunny climate if you can tolerate the lost liquidity and have a way to realize the savings.

  64. iLikeDirt | | #64

    Of course this was just the heating season; my cooling season is about 2-3 months long and those costs have to be factored in as well. But the point is that a cheap, no-HVAC-tech-required mini-split is already very competitive with the expensive ones in many markets and use cases, and can often beat them. A $700 1/2 or 3/4-ton plug-in model would sweeten the pot even more.

  65. Expert Member
    Dana Dorsett | | #65

    Nate: "uninsulated slab, R-14 walls, R-50 attic with ductwork, U-0.26 windows." is slightly better than code min (mostly due to windows). At 1300 square feet, that's barely more than half the median 2,467 size of new houses built in 2015.

    Given your high PV capacity factor you would be getting a significant boost out of passive solar gain, far more than where most US cool-climate denizens are. Rather than "...only a fraction of the USA..." the dim zone covers the lion's share of the US cool/cold climate population. Illinois alone has as many residents as all of sunny zone 5B, not to mention NY / NJ & New England or MI /OH / IN / MN. Yours is the exception, not the rule- take a peek:

    At H1 2016 PV prices $2000 would buy you 667 watts of PV, not 500 watts, and yes, in higher insolation areas the PV math works favorably relative to paying higher efficiency heat pumps than in New England type insolation, but as the NREL map indicates, the average PV capacity factor in most of US zones 4A-7A is considerably less than it is in your location.

    Electricity costs in most (but not all) of those states is at or above the 12.58 cent national average too.

    It won't be many years until PV becomes something of a no-brainer investment even in the less sunny population centers, given that it's currently $3/watt, 64% of which is soft costs unrelated to hardware & insulation costs:

    The 15 years is a minimum, not a typ lifecycle expectation for better-class mini-splits, and well over what I would expect from a second or third tier vendor. A replacement cycle on a better class mini-split doesn't cost nearly as much as a new installation. The power wiring, refrigerant line plumbing and mounting would be good for 50 years or more. The higher efficiency and capacity of new-improved better-class replacement unit may have to be weighed against the other factors such as electricity price inflation/deflation and improvements in lower tier mini-splits at that time.

    I couldn't find even a submittal sheet, let alone extended capacity tables or engineering manuals on the Mr. Cool DIY (or their other) units, so there's no telling what capacity they might have at 99% outside design temps in zone 5 or cooler. The stated 13,000 BTU/hr heating capacity for HSPF4 means that it's good for that much at +17F, but that's below the mean January temp for most zone 6 and colder locations. (It's also 23% less capacity at +17F than the Fujitsu 12RLS3). Even zone 4 NYC/Long Island's 99% bin is colder than +17F (if only by a couple of degrees.) No indication of how it manages defrost cycles in cold climates, or whether it has crankcase heat to keep it from self-destruct when it's really cold out, etc. Different documents for the 1-ton indicate HSPF 8.2 and HSPF 8.8, not sure which (if either) is actually correct. Without more information it's hard to really size the thing for even the cool edge of zone 4, and impossible for zone 5 or colder.

  66. iLikeDirt | | #66

    This is a great discussion. And I think you're actually proving my point: the better mini-split units make more sense where it's colder and cloudier and where electricity is more expensive than average. But again, that's only a fraction of the country. It may be that my personal location is uniquely suited for PV, but there are plenty of other regions of the country that have different advantages. In Seattle, electricity is half the national average, for example. And in the south, extreme low-temperature heating capabilities are not important.

    Even given that a nice Fujitsu unit is likely to outlast a Mr. Cool and be cheaper to replace than it is to install for the first time, that still doesn't change the fact that with the right combination of variables (climate zone, insolation, electricity cost, heat load, etc), a cheap unit can be cost-competitive for someone both buying and paying the bills over the product lifecycles when you take into account alternative uses for the saved money. And of course if you're the buyer but not the user (i.e. the builder), a cheap unit that works is a no-brainer even if the total lifecycle cost might be higher because it's the customer who pays those costs, not you; the upfront cost savings are just money in the bank. If your perhaps-slightly-better-than code-min project can get away with an HVAC budget of $5-6,000 for a zoned mini-split system with one head per bedroom and common area that can be installed without an electrician or HVAC crew, that would seem to beat the pants off of a typical single-zone gas/AC system for $10,000, no? Compare that to a mini-split bid of $3,000 per head that would cost 50% or more than the conventional ducted bid. There's your "tunneling through the cost barrier," right there. Sure, this won't work in Maine, today. But today's tech would seem like it'd do just fine in most places south of the Mason-Dixon line. Also, you don't need to waste square footage on a furnace room if there's no basement, and you don't need to torture yourself trying to get the HVAC crew to build ducts in the conditioned space.

  67. Expert Member
    Dana Dorsett | | #67

    Nate, I don't think we really disagree on much. The "only a fraction" part I really do take issue with.

    ONLY a fraction?

    It's a LARGE fraction- possibly the LARGEST fraction of the US from a total heating/cooling energy use point of view. It's over 1/3 the US population and probably 2/3 to the heating & cooling energy use (statistics drawn from thin air, but probably not insanely far off. :-) )

    One head per bedroom is insanely oversized, even for code-min houses, (maybe not for some retrofits), and by insane oversizing the lack of modulation would mean it never hits it's efficiency numbers. The $3000/head figure would also be high- name-brand multi-split systems with half-ton & 3/4 ton heads are running no more than ~$2500/head on retrofits, for those who fell in to the "it needs one head per room" trap. Most Net Zero houses can be heated/cooled with one head per floor, but probably not with a Mr Cool in a zone 5 location. South of the Mason-Dixon, sure, but most buyers of new homes wouldn't be happy with having to replace it in 10 years or less.

    As I stated previously, the cheap pre-charged DIY units are extremely popular all over lower income countries in Asia and Latin America, where the concepts of warranty & distributor service don't really exist, and the longevity and low-temp capacity expectations for the equipment are appropriately low, and self-installation is a given. Cheap DIY mini-splits are the up-town classy thing to have in Afghanistan or Iran or Iraq, where home heating is typically point source and not always on. The fact that they crap out and have to be replaced is accepted in those markets. Slapping Wi-Fi interactivity onto a goat doesn't exactly transform it into a thoroughbred, but can the goat still get there? Sure, with caveats.

    And I agree that these units work just fine south of the Mason -Dixon, which is where most of the distributors for lower tier Chinese mini-splits are located. Friederich (HQ in TX) has been slapping their name on a Chinese DIY unit for a few ears now (not sure who manufactures it), but at a somewhat higher price point than Mr. Cool:

    Klimaire (HQ in FL) has also been selling third-tier DIY mini-split heat pumps for under a grand in the US for years.

    If you really want to go there, it can be done, but I have a feeling low-margin tract house builders don't want the reliability risk with the potential support costs of products they are less familiar with, and supply chains that require using Alibaba to find the hopefully correct parts.

  68. iLikeDirt | | #68

    Sure, a lot of people live in the northeast and upper midwest. But this is GreenBuildingAdvisor, not "FrigidNorthBuildingAdvisor!" Often there is a pronounced focus on this region of the country to the exclusion of most others, or even acknowledgement that things are regionally-specific. It doesn't have to work in that region of the country to be feasible or even desirable elsewhere. But this is a tale as old as time: Yankees seeing themselves at the center of the universe. :-)

    What's the technical barrier to 1/2 or smaller ton mini-splits that are suitable for bedroom installation? The reason why I focus on this is because there are codes in many places for minimum heating and cooling levels for bedrooms and other inhabited spaces. Electric baseboards don't work for cooling, which means a mini-duct solution for the bedrooms might be needed if you're not using a central system, which raises the cost a lot because it's hard to find competent HVAC firms willing to build the necessary high-quality ductwork. Once you're already there, it probably makes sense to ditch the mini-splits and just acquiesce to crappy central ductwork and other more familiar methods. The prospect of dirt-cheap, appropriately-sized mini-split heads provides a way out of this Gordian Knot. I hear what you're saying about the lower quality of these units, but frankly the American construction market is not exactly awash in high-quality products and methods as is, especially the tract house market. The ubiquitousness of things like OSB, asphalt shingles, plastic housewrap, and vinyl windows without glazing pockets can easily make us forget how terrible they as building materials. There's definitely focus on the boutique luxury market here, but back in the real world, American houses are mostly awful, especially those built in the last 70 years. Crappy mini-splits may just be the perfect match for crappy American houses.

  69. GBA Editor
    Martin Holladay | | #69

    "Crappy mini-splits may just be the perfect match for crappy American houses."

    OK -- you've got your rallying cry. Now go out and found a new movement.

  70. Expert Member
    Dana Dorsett | | #70

    Nice! :-)

    (@ Martin)

    Nate: Heating requirements in codes are pretty universal, but I've yet to see a local code with cooling requirements. Can you point me to one?

    In a better than code house meeting the heating requirement with a point source ductless isn't as hard as it might seem, especially at below the Mason-Dixon 99% outside design temps.

    The standalone half ton Mitsubishi FH06NA has a nice low minimum modulated output, but not a nice low minimum price tag, maybe a $100 less than the 3/4 tonner. IIRC there are some Samsungs & LGs that go even lower (on both modulation level and price), but the model numbers aren't yet imprinted on my brain. The minimum modulated output of Mitsubishi multi-split compressors are over 7000 BTU/hr, comparable to the Fujitsu multi-splits. So even if the heads can all modulate down to something really low, a house with a design heat load under 15,000 BTU/hr isn't well served by the one-head per-zone approach, since the compressor in the middle of it all can't modulate low enough. Fujitsu RLFCD mini-ducted solutions all modulate down to 3100BTU/hr out (heating or cooling) independent of and work pretty well for better than code houses for dealing with doored-off room heating requirements. They're not very expensive to install for new-builds (cheaper than a gas furnace +1.5 cooling coil) but can be a PITA as retrofit. Getting them by the code inspector without resistance backup is difficult if your outside design temp is below -5F, since that's where the extended capacity tables end. But for south of Mason-Dixon location that's not an issue, and it can be both cheaper and more appropriate than a Medusa-class mulit-split that only modulates down to 6-7K at the compressor, or a half-dozen half-ton mini-splits.

    Far from thinking of New England as the center of the universe, I think of it as the "average" insolation levels "typical" of the populated US cool climates. Coastal WA & OR are a bit dimmer than the US average, and while zone 5 & 6 & 7 portions of NV /WY/CO/UT are quite a bit higher than the US average, in relative proportional terms "nobody lives there!" ;-) (And, I'm only a Yankee by current residential address anyway- followed a woman home from school one year... long story. :-) )

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