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Musings of an Energy Nerd

A Conversation With Wolfgang Feist

Questions and answers about the Passivhaus standard

Striving to explain the Passivhaus standard to American audiences: Dr. Wolfgang Feist began his tour of the United States in Boston, where he addressed a crowd at the Boston Architectural College.
Image Credit: Martin Holladay

Dr. Wolfgang Feist, the physicist and founder of the Passivhaus Institut in Darmstadt, Germany, began his U.S. speaking tour with a presentation and panel discussion at the Boston Architectural College on October 23, 2010. Among the other speakers at the event were Katrin Klingenberg, the founder of the Passive House Institute U.S. in Urbana, Illinois.

After suffering some public relations stumbles in the past, Feist and Klingenberg have polished their presentations. In Boston, they steered clear of the awkward exaggerations and red herrings that have marred previous U.S. discussions of the Passivhaus standard.

When I first interviewed Dr. Feist in December 2007, he explained, “As long as you build a house in a way that you can use the heat-recovery ventilation system — a system that you need anyway for indoor air requirements — to provide the heat and cooling, it can be considered a Passivhaus.” Since this method of heat delivery has proven to be extremely difficult in the cold climates of North America, many American designers were confused by Dr. Feist’s insistence on it. Refreshingly, Dr. Feist made no mention of this method of heat delivery in his Boston presentation.

In marked contrast to claims made at the 2009 Passive House conference in Urbana, Illinois, where the keynote speaker, Günter Lang of Austria, falsely claimed that Passivhaus buildings don’t require a heating or cooling system, Dr. Feist was forthright and candid during his stay in Boston. “In the heating climates, a Passivhaus building is not a zero-energy building — you still need to heat it,” Dr. Feist told his American audience. He later explained that, if you are building in a hot, humid climate, “You will need a small cooling system or a small dehumidification system.”

The five elements of a Passivhaus building

In his presentation to the Boston…

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  1. mike eliason | | #1

    great questions
    great questions, martin. i'm wondering if your thoughts on PH have shifted at all based on this, or if you still have the same reservations?

    my one critique is that 'EU windows are expensive'. compared to wood windows mfr'd in the US, they're really not - especially when you take quality and performance into account. but comparing to fiberglass, high performance wood windows from the EU will be pricier. i've worked on a number of homes with window packages @ $100/sf+, for double pane windows that weren't the tightest construction. i don't see how a client wanting attractive wood windows that perform really well is any different from a client wanting well designed plumbing fixtures or high quality finishes.

  2. Pat Murphy | | #2

    Internal Insulation
    Feist notes re air tightness for retrofitting "I think you should do what you can on a reasonable level. We were surprised in Europe to learn that a thing like the airtightness standard was possible in all the projects we have done so far. They all came under 1 ACH at 50 pascals. If you are that tight, of course you need a ventilation system."

    And then says "Insulation is a different thing. With some buildings you can do external insulation. But there are lots of buildings where you cannot do external insulation. And internal insulation is much more difficult. You will never reach the Passivhaus standard with internal insulation, because of thermal bridging."

    That seems like a bold statement to make. I can think of some ways to insulate to the inside that would minimize thermal bridging. What do you think Martin? There are people who are trying this.

  3. GBA Editor
    Martin Holladay | | #3

    Passivhaus retrofits with interior insulation?
    I haven't done it -- nor have I run PHPP on an existing building. So I don't know. But I have no reason to doubt Dr. Feist.

    Surely it depends on the climate: in Italy or California, interior insulation may be enough to bring an existing building into compliance with the Passivhaus standard. But certainly in a cold climate, it would be tough to reach Passivhaus performance without insulating the outside of the shell.

    If the floors are framed with wood joists, then embedding the ends of the floor joists in insulation puts them in danger of rot, because the ends of the joists are now cold.

    If the floors are concrete slabs, the slabs will remain brutal thermal bridges that rob your building of heat.

  4. Richard Ugarte | | #4

    What is the PassivHaus "standard" now?
    I thought the Passivhaus standard was quite simple: if you can meet your heating and cooling loads by heating and cooling only the required ventilation air, as your forced air system, then you have a Passivhaus. It was expected that to accomplish this "standard," you will in all probability need to be below a certain ACH of air tightness and above a certain R-value for the enclosure, but these will vary by location - the standard is the same: fit it in the ventilation requirement of a dedicated outside air system. From what I read, this was claimed as the defining feature that made the Passivhaus standard different from just saying it was a low energy house at an arbitrary level: condition the ventilation air and if that is sufficient for comfort, you have a Passiv house.

    Did I misunderstand the standard? Is this no longer the standard? Is Passivhaus just 'really low energy use house' now, one of many? I don't see in the interview that Dr. Feist defines the standard, but simply emphasizes "good performance."

  5. GBA Editor
    Martin Holladay | | #5

    Response to Richard Ugarte
    Richard Ugate,
    An outline of the requirements of the Passivhaus standard can be found in my previous blog, Passivhaus For Beginners.

    Here are the most important points: To meet the standard, a house needs an infiltration rate no greater than 0.60 AC/H @ 50 Pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 watts per square meter and windows with a maximum U-factor of 0.14.

    Although the Passivhaus standard has never required space heat to be delivered through ventilation ductwork, Dr. Feist has muddied the waters considerably by telling many journalists, designers, and builders that Passivhaus buildings must do exactly that. When pressed, the Passivhaus Institut has replied that in fact space heat may be delivered by any means you want -- electric resistance baseboard heaters, gas space heaters, pellet stoves, furnaces, or boilers -- in spite of what Dr. Feist said.

  6. J Chesnut | | #6

    Much appreciated article
    Much appreciated article Martin and Chris.

    I think we can all agree on the 5 elements of Passivhaus and I agree with your list of challenges that PH proponents face. I'll look forward to 2011 when regional differences will be addressed. I still don't understand how the 15kWh/m2 was arrived at and if it makes sense for all climates.

    One surprise for me was Dr. Feist's remark that when retrofitting old building he puts the priority on insulation before air tightness. This may be the most expedient way to address heat loss but it seems more prudent to tackle the air tightness to avoid moisture concerns in the assembly.

    Martin I think your point about economical HVAC packages is worth further debate. I think spending an additional $5K-$10K is worth the reduced energy consumption though I am not as knowledgeable about all the alternatives and their performance comparisons.

    Recently a PH standard for retrofits was distributed. I don't have the manual with me but it includes less rigorous ACH and heat energy use standards than the new construction targets. I'm confused why Dr. Feist didn't mention this and in fact this wasn't a good idea to have a separate standard.

  7. Wolfgang Feist | | #7

    Heating systems in passive houses
    Really do not know what is creating such a confusion. The definition never changed - it's a performance standard, it never was different - 15 KWh/m² Heating / 15 cooling, 120 primary energy for residential buildings. And: It was always open which systems to use. Although, there is a motivation to use these figures: the 15 & 15 is such a low requirement, that heating/cooling is no longer a big issue. The compact systems (Martin calls "magic boxes") become possible. I'm still convinced, that this is one of the best and most economic solutions - never claimed it's the only one.

  8. Kevin Dickson, MSME | | #8

    "You Don't Need a Heating System"

    You say you haven't seen it, but the H4H NREL house in Arvada proved it with off the shelf equipment, installed, for about $1000. The heating system in that type of house would normally cost $6k.

  9. user-869687 | | #9

    The challenge of a hot climate
    Wherever a building is located there will be some degree of solar heat gain plus incidental sources of heat from appliances and bodies. In a cold climate these heat sources subtract from the space conditioning energy demand, whereas in a hot climate they add. This simple fact challenges the strategy of achieving very low energy use through superinsulation. In a hot climate the indoor temperature could rise above the outdoor ambient when windows are closed and A/C is not running, reversing the delta-T. Of course with A/C running (and a positive delta-T) the insulation does reduce heat gain through the enclosure. However in hot areas it is necessary to address internal gains, and some will be unavoidable (human activity). For some areas / occupancies it may be impossible to achieve PH energy targets while actively space cooling.

  10. user-869687 | | #10

    Another unavoidable heat source
    Also on the list of unavoidable and unhelpful sources of heat is lighting, either through windows or artificial. Even with appropriate glazing and efficient lighting design, light = heat. If every watt of light becomes work for the air conditioner, window sizes and locations must be strategic. It could come down to choosing larger windows and leaving them open rather than smaller windows to reduce cooling load.

  11. GBA Editor
    Martin Holladay | | #11

    Response to J Chesnut
    J Chesnut,
    I agree with you. I was also surprised at Dr. Feist's retrofit advice: first add insulation, then address airtightness. That is the opposite order from the way that weatherization workers have been approaching buildings in the U.S. for the last 30 years. Here in the U.S., the order of the retrofit work is always: start with airtightness, then address insulation.

    The classic problem would be in an attic. If you install lots of insulation in an attic before sealing the ceiling plane, you've made a mistake.

  12. GBA Editor
    Martin Holladay | | #12

    On economical HVAC equipment
    Kevin Dickson and Dr. Feist,
    Kevin, the house your are referring to -- the Habitat for Humanity house in Wheat Ridge, Colorado -- does indeed have a very low cost HVAC system. But it's not a Passivhaus building.

    It is one of the houses that I was thinking of when I pointed out that the most innovative thinking on low-cost HVAC equipment is coming from builders outside of the Passivhaus community. I'm also a big fan of Carter Scott in Massachusetts, who is heating his houses with ductless minisplit units (one outdoor unit, two indoor units, $5,000 installed cost) and ventilating them with a single Panasonic WhisperGreen fan (11 watts, about $120). Like the Habitat house in Colorado, Carter Scott's homes are not Passivhaus buildings.

    Katrin Klingenberg did a good job keeping the equipment costs relatively low for her first house -- except for her HRV, which was imported from Germany at great expense.

    Dr. Feist keeps returning to the idea of the "magic box." When I wrote an article on these devices, I tracked down how much they cost. According to Barry Stephens, a Zehnder ComfoBox costs about $18,000 in Europe — not including the ground loop for the ground-source heat pump, which can easily cost $10,000 or more. A magic-box appliance from Drexel und Weiss costs about $25,000 in Austria. So it appears that the Europeans haven't yet figured out how to solve the cost problem yet.

    I don't want to beat up the Passivhaus people too much on this issue; I think eventually we'll come to a consensus on this, and designers will find clever ways to address this. Here's my prediction on the consensus:
    -- Heating and cooling with a Japanese or Korean ductless minisplit.
    -- A very simple ventilation system, with or without heat recovery.

    Unfortunately, some of the Passivhaus designers have been led astray by the lure of the best, state-of-the-art European equipment, which is extremely expensive. I was glad to hear Dr. Feist say that it's not necessary to go down that road. We can find our own North American solutions to these problems.

  13. GBA Editor
    Martin Holladay | | #13

    Response to Thomas Jefferson
    You have very clearly explained the great challenges facing designers of hot-climate Passivhaus buildings.

    Most hot-climate buildings with a slab-on-grade foundation don't include any insulation under the slab, because ground coupling lowers cooling bills. That's one example of a part of the shell that clearly doesn't benefit from insulation in a hot climate.

    The traditional tropical solution to this problem was:
    -- Put the house on stilts;
    -- Build a massive roof with very wide overhangs for shading;
    -- Open the house to any available wind by providing large openings without any glazing.

    In other words, you don't want a superinsulated building. Of course, you still have an indoor air temperature which equals your outdoor air temperature. So if it's 100 degrees outside, it's 100 degrees inside.

    If you want your interior temperature to be 72, then you need air conditioning, and the design challenges increase tremendously. You've got a refrigerator, a kitchen stove, a water heater, lots of lighting, a television, and several computers. As you point out, all of these internal heat sources help you in Minnesota but hurt you in Phoenix.

  14. Wolfgang Feist | | #14

    air tightness AND insulation
    Have I said insulation "first"? :-) Can't be true, because that has again always been clear from the very beginning and well presented:
    - Yes, in most cases insulation is more important than airtightness (with respect to the energy balance). That is why we superinsulate (all adapted to the climate)
    - AND: In order to avoid structural damage an exterior component HAS TO BE airtight. Period.

    You do that together, that is what we have done (in practize, not just in theory) and it is what we recommend - and that was my statement, you can read it everywhere on passipedia because that is just very simple building physics. Martin, we should not confuse people with respect to this. May be, a controversy (you like controversies?) is a tool to make these topics interesting - so, if that’s your goal, thank you.

  15. GBA Editor
    Martin Holladay | | #15

    Response to Wolfgang Feist
    Dr. Feist,
    Thanks for your clarification; I appreciate it.

    I stand by the accuracy of my reporting, however.

    I think this was a simple misunderstanding. When you said, "If you start with an old building, the first step is always insulation. Then the next step is airtightness," the meaning was, "Most of the heat loss is due to low insulation levels. The second most important heat-loss factor is air leakage."

    Again, thanks for clarifying.

  16. Wolfgang Feist | | #16

    air tightness AND insulation
    Good that we agree again - the "first" was never meant to be a timeline order. Our language is sometimes not accurate - but we both know, what the science behind it is.
    AND: There might be a difference between Europe and the US - old buildings in the US are sometimes extraordinarily untight (because most Central European constr. is masonry with plaster, these ones "start" with n50 in the range of 3 to 6 ACH - not so bad, but still by far not good enough.

  17. Pat Murphy | | #17

    I was a bit surprised by your
    I was a bit surprised by your comment on the ends of the floor joists getting cold. I had not though of it. There is a pattern here now to close off the vents to avoid moisture and then spray or insulate the joists at the mud sill. Won't this popular technique make the joist ends colder.?

    Dr. Feist noted: "Good that we agree again - the "first" was never meant to be a time line order. Our language is sometimes not accurate - but we both know, what the science behind it is" AND "There might be a difference between Europe and the US - old buildings in the US are sometimes extraordinarily untight (because most Central European constr. is masonry with plaster, etc."

    There are close to 120 million homes that are going to need retrofitting since I don't think we can replace them with passive homes. It seems very important to figure out how to bring them near the passive performance level. One thing that I am only beginning to understand is how important air tightness is to the structural issue rather than just the air quality issue. I think when we understand more about this, that retrofitting solutions may be discovered.

    These dialogs between you and Feist are very valuable. I hope he follows and participates in the thread throughout his visit.


  18. GBA Editor
    Martin Holladay | | #18

    Damp joists
    The problem with cold joist ends that get damp and rot is most severe with old masonry buildings that have joists that sit in beam pockets. If the building is uninsulated, there's a lot of heat flow through the bricks, and the joists stay dry. Once insulation (especially fibrous insulation like fiberglass batts) is installed on the interior of the building, the ends of the joists are cold.

    If indoor air (that is, warm humid air) filters through the fiberglass insulation and contacts the cold masonry beam pocket, you've got rot. That's one example of how interior insulation can take a building without structural problems and turn it into a building with structural problems.

  19. kim_shanahan | | #19

    principles vs certifications
    I was heartened to read Dr. Feist believes the principles of the the Passive House have more importance than the certification. With the dominance of ResNet and HERS ratings in our American market, especially as they relate to tax credits and protocols like Energy Star, it will be quite some time before builders switch to Passive House certifications. In the meantime, we have much we can learn and experiment with. Attention to the envelope, sensible design, and energy efficent air-exchanges are clearly the low-hanging fruit. The efficacy of the individual components will come in time, and as Dr. Feist points out, they should come from small and medium sized entrepenuers who devlop their products first and get their certications second.
    Great article and great interview.

  20. J Chesnut | | #20

    Response to Dr. Feist
    Thank you for your contributions and clarifications to this discussion.
    I lived a couple of years abroad and understand the need to understand each other rather than hold each other to rigidly to the words we use.

    I am excited about the availability of a energy modeling tool such as the PHPP that includes the ability to factor passive solar gains into the design. The Passivhaus discussions in the US have been very productive.

    To Martin's defense, it isn't a matter of creating controversy around the subject but taking the introduction of the PH standard here seriously and scrutinizing it in order that we who are using it accurately understand it rather than uncritically stand behind the cache of the latest label on the green scene.

    PHIUS could use a regular web presence like Martin to elucidate the finer details of the energy modeling capacity of PHPP. I think it is important too to offer the translations of the German DIN references in the PHPP user manual or point to equivalent American standards.

    I don't know if the priority should be to make the PHPP easier, but instead to offer support so that users are confident they are using the software 100% correctly.

    Thanks again and I welcome the introduction of the PH standard to the US.

  21. Pat Murphy | | #21

    Interior Retrofit
    Thanks for your comment re masonry pockets.

    To continue the dialog (or start it) on super-insulating to the interior, I noted that in your Oct 10 commentary on History of Superinsulated Houses in North America you used a graphic from The Super Insulated Retrofit Book so obviously you are familiar with that work. The 30 page chapter entitled Interior Retrofit has a myriad of details re thickening walls to the interior including ways of installing vapor barriers and dealing with the joists. This was a Canadian book which may give it some more credibility. Do you think these are valid approaches? Do you think a room by room retrofit over many years is a possible approach to the existing stock? Are you familiar with Linda Wiggington's Thousand Home Challenge and do you think it has potential?

  22. J Chesnut | | #22

    Response to Kim
    Yes I think we can all agree on the 5 elements of a Passivhaus Martin bullet points in this blog.
    Martin blogged recently about the historical debate between superinsulation versus passive solar.
    Now that these concepts are married I think the debate will move to 'how fine tooth a comb'.

    ResNet and HERS ratings are less sophisticated than the PHPP in terms of accurately modeling the energy use of new construction. The real advance of the PHPP is that it is a design tool that informs the design of a building a the critic stages of schematic design. Leveraging passive solar gains can be optimized and the thermal envelope and mechanical can be fine tuned to achieve even greater levels of energy reduction potential.
    The most vocal opponents to PH don't comment on this aspect. They instead point to the air tightness levels, argue the arbitrariness of the standards energy use requirements and warn against overuse of petrochemical insulation.
    Its the PHPP that coordinates the 5 elements of Passivhaus into an optimized whole and makes the performance of the whole system more significant then the performance of the components.

  23. GBA Editor
    Martin Holladay | | #23

    More on interior insulation for Pat Murphy
    I've already written a blog on this topic for next week, titled, "How Risky is Cold OSB?"

    Dr. Feist and I agree that exterior insulation is the best retrofit strategy.

    Adding insulation to the interior of a cold-climate house is risky, because you are making your sheathing colder, and therefore raising the risk that your sheathing will be damp. This is especially risky if (1) you don't have a tight interior air barrier, and (2) you have a cladding like stucco that is slow to dry.

    There are ways to reduce the risk. These measures include doing your best to create an interior air barrier -- an almost impossible task in a typical existing house -- and adding a ventilated rainscreen gap between the siding and the sheathing.

    But if your retrofit work requires replacement of the siding, it obviously makes much more sense to install thick exterior foam, which is far less risky than thickening your walls from on the interior.

  24. Katrin Klingenberg | | #24

    I sometimes wonder...
    ...after reading your reporting if I actually attended the same event. Not that I question the "accuracy of your reporting". Certainly you are free to put your spin on things, add and omit whatever you feel appropriate. To make it interesting :)

    In 2007 our 2nd Annual North American Passive House conference was called "The path of high performance; from the 70s until now". We had invited Harold Orr to be our keynote speaker to present on his early work as well as on his ongoing deep energy retrofit in Regina. Bill Rose presented on the history of the Small Homes Council and the low-Cal house. Opening the conference I quoted William Shurcliff's press release, yes the same one that you keep quoting, I read too and own probably similar books. We then invited you last year to the PH conference to present on the history to repeat that content for those who had previously not been aware of it. If you like to put the spin on things that you educated me, that's fine if it makes you feel better :) You will find that our effort to honor those North American roots and to connect them to the ongoing advances nationally and internationally has been consistent from the beginning of our organization and will again be a topic at the upcoming conference. Your red herring issues are all issues that are documented and researched quite well. They require a more in depth discussion forum and knowledge level. An introductory presentation is aiming at a discussion on a more general level. I am stating the obvious. Maybe you should come to the conference in Portland, where those topics will be discussed in much more depth. You could get some of your questions answered.

  25. GBA Editor
    Martin Holladay | | #25

    Katrin, My apologies
    I am indeed very sorry that I am unable to attend the conference in Portland. It sounds like it will be a great conference.

    I'm sorry to have implied that my writings influenced your presentation. I will correct my blog accordingly.

  26. GBA Editor
    Martin Holladay | | #26

    On red herrings
    I agree with you that there is plenty of research and information available on the "red herrings" issues. I do my best to contribute to educating the public about superinsulation and the Passivhaus standard. Like you, my intent is to share accurate information to help educate builders and designers.

    However, there is no doubt that confusion remains. As evidence, just look at the question posted on this page by Richard Ugarte. This was Ugarte's misunderstanding: "I thought the Passivhaus standard was quite simple: if you can meet your heating and cooling loads by heating and cooling only the required ventilation air, as your forced air system, then you have a Passivhaus."

    Here's another example: as recently as two weeks ago, an editor at Fine Homebuilding magazine -- surely someone who is more in the loop than the average Joe at the local lumber yard -- expressed puzzlement when I mentioned a heating system for a Passivhaus building. He said, "But I thought that Passivhaus buildings don't require a heating system."

    My point is, the Passivhaus standard has, in the past, sometimes been presented in ways that have confused builders and designers. Not everyone understands the standard as well as you -- even though, as you correctly point out, these "are all issues that are documented and researched quite well."

    I hope we can agree that it's in everyone's interest to present this information to the public. Because after all, we share the same goal: to promote greater adoption of superinsulation techniques in North America.

  27. Katrin Klingenberg | | #27

    Thank you!

  28. Richard Ugarte | | #28

    From the Passivhaus Primer online:

    "To achieve the PassivHaus standard the energy required for space heating
    must not exceed 15 kWh/(m2 a) – this is the overarching requirement."

    Now, why this value of 15-15? The Primer says:

    "1. The figure of 15kWh/(m2 a) has been arrived at from calculating the
    maximum amount of heat that can be delivered using the fresh supply air at
    the minimum required ventilation rate."

    It seems to spell out that the 15-15 was arrived at, not by an arbitrary performance level, but by asking how much heat or coolth you can deliver with a dedicated outdoor air system (DOAS). The Primer then spells out the limits that the air itself imposes:

    "It is limited to 15kWh/(m2 a) for two reasons:

    1 The temperature of the fresh incoming air cannot exceed 50°C – if the
    fresh air is delivered at a higher temperature than this problems can
    occur with the indoor air quality (e.g. burning smells caused from the air
    scalding dust within the ductwork).

    2 A comfortable indoor temperature (20°C) needs to be achieved in areas
    with low ventilation rates – this means that only a certain amount of
    heat can be supplied without exceeding the 50°C temperature limit.

    Without achieving the PassivHaus space heating requirement of15 kWh/(m2 a) or less, criteria 1 & 2 will not be achieved and thus it is not recommended to try and heat a dwelling using the fresh incoming air."

    Then the Primer says how the ACH and insulation requirements simply devolve from this 15-15 requirement:

    "Achieving a space heating requirement of 15 kWh/(m2 a) or less means that
    the following headline features are specified:

    • Super-insulation: opaque U-values must be less than 0.15 W/m2K
    • U-values for windows and doors need to be 0.8 W/m2K or less (for both
    the frame and glazing). This requires the window frame to incorporate
    insulation and triple glazing
    • Thermal bridging needs to be minimised, and ideally eliminated
    • Airtightness: n50 of 0.6 h-1 @ 50 Pa or less
    • Whole house mechanical ventilation with heat recovery (75% efficient or
    better, with a low specific fan power)."

  29. GBA Editor
    Martin Holladay | | #29

    On the origins of 15 kWh per square meter
    Richard Ugarte,
    You're right -- that's the explanation of the origin of the 15 kWh per square meter requirement. In a sense, it is a historical curiosity, however, and is not central to achieving Passivhaus certification, because the Passivhaus standard does not require a builder to deliver heat through the ventilation system. It's a tale that is of interest to Passivhaus historians, not Passivhaus designers.

    As I wrote earlier, you can design a house to deliver heat any way you want. As long as your heating load doesn't exceed 15 kWh per sq. meter per year, you are good to go.

    There are many reasons why delivering heat through ventilation ducts is irrational; I have explained them in my blog, A ‘Magic Box’ For Your Passivhaus.

    In that blog, I wrote, "Ventilation requires small air flows, while the delivery of space heat and cooling usually requires larger air flows — making the integration of these two functions illogical. In hopes of achieving a particular heat-delivery goal, a magic-box designer can be tempted to solve this technical challenge by overventilating. It makes more sense to optimize ventilation ducts for fresh air delivery without consideration of heating or cooling loads; combining these functions often results in technical compromises. Because of this last point, I predict that the long-touted Passivhaus recommendation to deliver space heat through ventilation ducts will eventually fall by the wayside — if not in Europe, then certainly in North America."

  30. Richard Ugarte | | #30

    Thanks, Martin, that helps me understand things better. You are allowed a minisplit, but your minisplit size is pegged to the ventilation air potential heat/coolth carrying capacity, as a foreign currency might be pegged to the dollar. And you find it illogical to put a fan coil in the ventilation fan where you could have a minisplit instead, and so not combine the functions in one apparatus. What is illogical about a fan coil? Isn't this just a very small (<=0.25 ton) forced air system with a return plenum coming from outside fresh air? Is this inherently illogical? I think I'm missing something you're saying.

  31. GBA Editor
    Martin Holladay | | #31

    On hydronic coils in ventilation ductwork
    There's nothing wrong with putting a hydronic coil in your ventilation ductwork. If that works for you, Bless you and Godspeed. It probably means you live in a relatively mild climate, however.

    Ultimate Air sells a hydronic coil designed to be installed in your ventilation ductwork. It only produces 8,700 Btu/h at full output -- that isn't much -- and even that output requires 200 cfm of airflow -- way more airflow than is typically used for ventilation. The numbers don't add up.

    Most homes are adequately ventilated with about 50 cfm of ventilation air. That a small air flow, so there's a limit to the amount of BTUs that you can add to the air flow with typical water temperatures. If you live in northern Vermont or Minnesota, it's hard to make this system work. If such a heat delivery system results in 16 inches of sub-slab foam, is the investment in the foam logical?

    I'm all in favor of any heating system that works. I tend to favor heating systems that are inexpensive to install, long lived, and affordable to operate. "Magic boxes" don't qualify -- yet. Some day they might.

  32. user-829148 | | #32

    One step better than bath fan ventilation
    We've been getting our renovations tight enough to need "Ventilation on Purpose" . It's true, a bath fan with a controller would be the cheapest solution ... but not by much. The Panasonic ERV gives 40 cfm and costs about $300. Most importantly it doesn't introduce negative pressures. (This system isn't ducted and introduces fresh air at a single point, requiring the regular duct system to distribute the fresh air.)

  33. Sean Wiens | | #33

    15kw Threshold
    Hi Martin,

    It was good meeting you at the BC Building Envelope Council AGM a few weeks back.

    Re Passive House, I believe you are being a bit misleading. You cannot choose whatever heat source you want and still hope to achieve the 120 KWh/m²/yr threshold requirement for all electricity demands. The point is, the homes are designed around being ABLE to heat them with nothing more than heating the air circulated by a high efficiency HRV with a small electric element or a brine geo exchange loop or a heat pump. This is not a pipe dream. It has been proven many times over. The rest of the requirements/suggestions just seem to be the best way to meet that requirement in a cost effective manner.

    The high efficiency HRV's that meet the 75% rating are already available in N.A. and it is expected that a PH Certified HRV and a PH Certified window will be available within N.A. within the next yr (local BC firm working with window manufacturer to produce certified window units and a HRV manufacturer has already delivered his unit to a testing facility for efficiency certification). It should also be pointed out that it is cheaper to import high efficient triple pane windows from Germany now compared to buy a lot less efficient wood high 'quality' dbl pane windows from N.A.

    An HRV is the only way you are going to be able to change the air enough times for hygienic reasons once you have achieved the .6 ACH and yet not pump all your heat outside as would result from any single fan system you try to install. HRV's are pretty standard on new construction in our area, so the added cost for a 'efficient' one is not substantial (<$1000??).

    The real issue is that the Passive House is one of the only 'green' models I have studied that tries to reduce energy usage by a substantial factor, instead of just building our normal junk and then putting contraptions on the roof to try and generate heat and power and call it 'Net 0'. Contraptions that costs many 10's of thousands of dollars, often have a limited service life, and often do not provide the performance promised.

    Anybody who builds a Passive House will easily meet the requirements of any other 'green' label you wish to throw its way and probably for a lot less money.

  34. Coyo | | #34

    State of our industry?
    I was very enthusiastic about Energystar, LEED and Green build and spend a lot of my time volunteering into these programs and promoting them over the years. There was so much good initially I had seen - and still do but things have become murky over the years and there is so much green washing and political infighting going on today it is simply sad. We are missing the point - and I see the same exact trend happening with the Passiv Haus standard over the last year. There is so much misinformation being produced and so much resistance build up against this standard that I really wonder sometimes...what are we thinking? Can't we just step away from our egos for a second and try at least to look at the big picture? Do we really need to defend - our science is better than your science? I know more than you do - and we are the ones who really invented it all?

    Is the Passiv Haus standard the holy grail for us to solve our problem in our building industry - I don't think so. We have a much wider spread of climates and a different culture and industry. Our building codes and regulations have a lot of issues untouched which are highly regulated and mandate in Germany. Passiv Haus can be a tremendous asset for us in regards to building highly efficient homes - but it does not help us with a much bigger problem we are still trying to tackle - unhealthy buildings. A many of common building product are very problematic. How many brand new homes we build today are still very toxic? These are the grassroot problems which led to LEED and Greenbuild - and these are very important problems to solve. Our health is priceless. We need to look at the big picture and if we want to see change we will have to stop working against each other and work together. Share and learn from each other - and not get caught up in questions of "who has the better answers".
    And we will need to adapt our market and realize it's potential. Drooling over high efficient magic boxes or windows from Europe and shipping building materials halfway across the world is not the right answer. And in my opinion it is missing the core of what we are trying to do with building high efficient buildings. Conserve energy demand, reduce carbon footprints - build more sustainable.
    There isn't anything sustainable about shipping windows from Germany to the States. The embodied energy in transportation costs is something we will never be able to overcome with the more efficient building we are trying to put together. It is tempting - I travel through Germany every year and visit many amazing projects and look at their newest innovative products with envy. But I believe it is crucial that we develop our own markets - in our very own communities. It might not be the easiest and fastest way to get us what we want - but we need to understand the economic importance of money spend in our direct communities and also the sustainability of the overall picture. I was able to work with many of our local vendors to produce what we need for high efficient homes right here in town or at least in state. Our small local window shop is building high efficient tilt turn windows for us now with any glassing we specify. We build our own "R-40 Arctic" entry doors with insulated fiberglass frames, VIP panels, cork laminate which are airtight and have a seven point locks system for the same amount of money it would costs to buy and ship a "Passiv Haus" door from Europe.

    And we need to get real about what an efficient building truly is and what can be done with proper planning, design and modern building materials if they are put together carefully. Five years ago I was proud of myself to build high efficient, super insulated "GREEN" homes with the highest energy rating in the State. Today I am amazed to see what is even possible in our extreme cold climate (Fairbanks, AK) and how efficient homes can truly be .. and I humbly learn something new every day and try to keep an open mind. Learning from the Passiv Haus standard and realizing its potential has been a major contribution to what our company is able to do today. Once you grasp the principle there isn't anything really difficult about the standard itself. It gives you benchmarks and tools to work towards and from there on it is just a matter of good design and building practices. Achieving 0.60 n50 is not difficult once you design the air layer and your crucial window and door opening correctly - and you keep a blower door unit and an IR camera in your tool trailer with your chop saw and your nail guns and treat them as what they are - tools to get the job done right. Excessive and unrealistic air tightness? If I pick out one of the improvements in our homes I would never back off from - this may be it. It is the most inexpensive energy measure there is - and it solves so many other issues at the same token. Stop your exfiltration and infiltration and all your wall problems are solved. Ventilation - heat distribution in a controlled environment become so much easier. Not convinced? Build to the Benchmark and see for yourself. Take the time to really learn about the Passiv Haus standard before dismissing it or ranting about it as being excessive and unfeasible. By now there is a lot of good information on the web in English - at everyone's disposal for free with your simple friend Google.

    Dr. Feist is here as an ambassador to encourage us to work together and even takes time to answer question here on GBA to help. I am very grateful for his willingness to spend his limited time on the road here to try to bridge the gap of misunderstanding which seems to widen instead of closing. And I don't believe he does so as a sales person - but as an individual who believes at what he is doing and is concerned with the global challenges we as humanity are faced with. From what I have seen and heard from him - as well as Katrin this is their sole motivation and they spend a lot of their personal time to stand up and make a stand. Looking at what is ahead of us in the near future is what keeps me going and motivated every day and what keeps me pushing the envelope from one project to the next. We all can make a difference - one step at a time. And it will take all of us to work together to really brings us forward...Let's build responsible, TC

    PS: Martin, Dr. Feist, Katrin & Mike and the PHUIS crew - and so many other unnamed and unknown amazing individuals who contribute every day for all of our benefit - thanks for what you do.

  35. GBA Editor
    Martin Holladay | | #35

    Response to Sean Wiens
    You wrote, "You cannot choose whatever heat source you want and still hope to achieve the 120 KWh/m²/yr threshold requirement for all electricity demands." I didn't mean to imply that a Passivhaus designer can ignore the 120 KWh/m²/yr threshold; of course not. All Passivhaus targets must be met, including the 120 KWh/m²/yr target.

    That said, I have been assured by Dr. Feist and Katrin Klingenberg that you can use any heating method you want, and any heating distribution method you want, as long as these energy use targets are met.

    That's great news about Passivhaus windows -- I look forward to being able to buy these windows here in North America soon.

    I'm a fan of HRVs, but I'm also paying close attention to builders experimenting with other clever ways of ventilating homes.

  36. GBA Editor
    Martin Holladay | | #36

    Response to Thorsten Chlupp
    Thanks very much for your comments; you make many good points.

    I was a little lost, however, reading some of your comments -- "There is so much misinformation being produced and so much resistance build up against this standard that I really wonder sometimes." Are you referring to GBA? I hope not. If so, point out the misinformation -- because we are striving for accuracy here and will be happy to correct any misinformation.

    "Take the time to really learn about the Passiv Haus standard before dismissing it or ranting about it as being excessive and unfeasible." Who's dismissing and ranting? GBA has focused its spotlight on the Passivhaus standard since this Web site was launched, and we've been promoting air tightness and thick insulation whenever the topics come up.

    Like you, I'm grateful to Dr. Feist and Katrin Klingenberg for their work, and was delighted to meet with them in Boston. Their work to encourage the adoption of the Passivhaus standard is inspiring.

  37. mike eliason | | #37

    CO2 and shipping
    "There isn't anything sustainable about shipping windows from Germany to the States. "

    as long as you are only making one shipment, and not multiple trips, this is bogus.
    the CO2 output of shipping windows from DE to seattle is about 600lbs
    (10,465 miles x 0.0887 lbs CO2 per Ton-Mile x 2/3 tons=619 lbs CO2)

    getting glass and windows that are significantly more airtight, have a better U-value, SHGC and VT than you can get in the states can easily save this - especially over 20+ years. this also means - especially here in the NW - you can get away with significantly less rigid insulation under slab and on walls. in an 800sf slab, you can save about 300 pounds CO2 for each inch of EPS i can eliminate, thanks to better glass.

    you are talking about less than 1% of total CO2 emissions for construction of a new wood house (about 40 tons). that is fairly insignificant by any standard.

  38. GBA Editor
    Martin Holladay | | #38

    Response to Mike Eliason
    Are you sure that these European windows really save significant amounts of CO2 compared to Thermotech windows with high-solar-gain triple glazing with two low-e coatings and warm-edge spacers?

    In other words, what are you comparing the performance of these European windows to?

  39. mike eliason | | #39

    i've run PHPP on 2 projects, and in each case, internorm and optiwin windows w/ glastroesch glazing outperformed thermotech and serious windows fairly considerably, especially on the qualitative front. in both cases, this allowed for less insulation around entire envelope.

    for our projects, the glazing has to be just right. thermotech's 322 gain and cardinal's LoE179#2#5 has less VT, and a much lower u-value than the glastroesch. and we don't particularly like Serious because of the color/VT issues. per PHPP, both the thermotech and cardinal glazing calculate to 18% over 4.75kBTU/ft2a. thus we'd would have to beef up wall, slab and/or roof insulation.

    that's not the direction we're interested in going, and a lot of people we talk to don't want fiberglass windows. if the CO2 cost of shipping superior windows is about the same CO2 cost of additional insulation, then client is going for the better windows.

  40. Jesse Thompson | | #40

    I've been curious about this
    I've been curious about this shipping question, so I quickly looked up some numbers on the internets. Wikipedia says 510 BTU / short ton mile for domestic water, 3,357 BTU / short ton mile for heavy trucks. These figures are probably incorrect, but that shows the huge efficiency differences between water freight and truck freight.

    If we order windows in Portland ME, and they come from Ottawa, Thermotech, Loewen, InLine etc (400 miles away) by truck, that's 1.3 MBTU / short ton (whatever that is).

    If we order windows from Germany (3,700 m) that ship to Boston and truck from there (100 m) , that's 2.2 MBTU / short ton. Worse, but not too bad.

    If we order windows from Minnesota, Marvin, Anderson, etc (1,400 m) by truck , that's 5.0 MBTU / short ton! We've just jumped an order of magnitude.

    Now someone just has to figure out how much energy a short ton of windows saves... Of course, it's a lot longer to go from Germany to Seattle, and they better not put them on a truck in New York.

  41. homedesign | | #41

    "State of our Industry?"
    I have been reading GBA since day one.
    Before that JLC Building Science Forum and before that FHB Breaktime.
    I think that Thorsten's recent post is the best post ever.

    ...what are we thinking? Can't we just step away from our egos for a second and try at least to look at the big picture? Do we really need to defend - our science is better than your science? I know more than you do - and we are the ones who really invented it all?

    It is a shame that Thorsten barely posts here because I think he has a lot to share.
    Thorsten, I hope you are working to publish more articles.
    As winter approaches I hope you will post here more often and try to ignore the "dark side"
    I want to hear more about your experiments.

    Our industry is in a "Sad State" and we are wasting a lot of time by not working together.

  42. mike eliason | | #42

    European PH windows

    took a stab at better numbers on how much EU windows could save. IF shooting for passivhaus, they could save as much as six tons of CO2:

  43. Coyo | | #43

    Window shipping Bogus
    Embodied energy is something very hard to truly quantify - if it is in manufacturing or transportation. I agree with that my argument may be bogus if you could ship directly from place of origin to your project directly as calculated in Mikes post and blog. If you're working on one pet project a year I also may agree. However, if this is simply becoming the way you build - and you build more than 10 "Passiv Homes" a year the dynamics change. Long lead and shipping times will become a road block on your projects. There will be shipping damages, mishaps on the job, warranty issues to deal with. Someone will need to respond and timing will be of essence. And it quickly becomes not feasible - and not sustainable in my humble opinion at least. If we want to be real about building homes to this standard then we will need to create our own market right here and we will need start now. We can easily manufacture windows of equivalent quality and efficiency in North America. The only reason that they are not being built right now is that there simply was never a demand for them from our industry.
    Economics: Being a small Builder we still easily spend 200K on windows per season. That is an insignificant amount for a bigger manufacture but it is a considerable amount of money for a small window shop. And even more important - it is a lot of money being circulated in our community, which is quickly multiplied, creates jobs and opportunities and is after all the basic foundation of economic growth and stability in our neighborhood. I personally at least believe that in these changing economic times focusing on localized growth and investment will be key.
    As any good designer of efficient buildings knows windows are the weakest link in your chain and therefor the most single important factor. They have a multitude of functions starting with essential day lighting, comfort and ventilation to the more complex function of providing the only free heat we ever get through solar heat gain if the glassing is appropriate (in a heating climate of course). So yes - it is very, very tempting to order better performing windows from Europe right now...and I struggled with this for some time. In the end I decided for myself that it is more important - and more sustainable to develop our own market which takes time, money and lots of effort but seems to be in the long run the better choice. Being at the end of the road in a very extreme climate might influence this choice maybe different - but at the end of the day I still believe we need to focus on the big picture. And part of this picture should be that any new home we build is at least 80% more energy efficient - everything else is IMO simply "bogus". The first thing we need for this step to take place in North America is - manufacture better windows :-)
    FYI - in my 14000 HDD climate it takes a window with a SHGC of 0.68 with U-0.072 to get to the magic Passiv# of 4.75 KBTUs(ft2/yr). - no amount of insulation anywhere else in the assembly can bridge this thermal weak point. One of the reason the Scandinavians bumped up there Passiv Haus numbers for the northern regions to 9.5 kBTUs(ft2/yr). Climate has a huge impact on your numbers - take your PHPP and change your climate to the included set for Yellowknife/Canada to see what I mean. With our current windows I hit 9.18 kBTUs(ft2/yr.), but that is as low as it gets until new glassing technology is developed. Otherwise it takes an R-20 shutter figuring in a 58% utilization factor of the shutter and a window with a high SHGC of min 0.54 - better above 0.60...Being the stubborn German as I am I overcame this hurdle (maybe!) on my latest project with R-20 to R-40 Thermal shutters on all windows. Typing this I can hear Martin already cry out "but they don't work!". Yup, I know it all has been tried before - but I guess some of us just don't listen. After I spend all year modeling and playing around with 4-5 ply glassing configurations to get up to R-14 glassing values I concluded that at today's technology we cannot build windows efficient enough without limiting the one factor which is IMO the most important of them all in a heating climate - the solar heat gain coefficient. I simply don't like to use anything below 60% on south facing windows heat just can't be beaten in this day and age where nothing else in life comes for free anymore. And once a window is installed you can't change your SHGC - but you can cheat your U-values with a thermal shutter. That's my theory for now and something which was for me at least worthwhile to explore further. Come spring I will have a more educated opinion and a pile of data and firsthand experience to see if it is a feasible means to higher performance buildings Far North - or a simple dead end. Anyways, enough of my ramblings. TC

  44. Coyo | | #44

    Response to Martin
    Martin, I don't see where I pointed fingers at you or GBA in my post. I thanked you for your contributions at the end. I am sometimes simply frustrated to see our industry go backwards. How you present your information is not up to me and you have to be the judge of your writings and your style. How others read and interpret this information will always vary and be personal. And as long as discussions are constructive and on topic they are very valuable. However at least in my opinion discussion here on GBA often times just turn into personal vendettas and get way out of hand. Something I personally don't need to be part of in my very limited spare time. All of which of course has nothing to do with this particular discussion about your interview with Dr. Feist.

  45. GBA Editor
    Martin Holladay | | #45

    Response to Thorsten
    Thanks for the clarification, Thorsten. I appreciate it, and I agree.

    Your advice that we should all try to work together is very valuable. How to manage a Web-based forum so it is open, inclusive, supportive of free speech, and still avoids the "personal vendettas" you mention is a tricky balancing act; here at GBA, we're still imperfect. We're trying, however.

  46. Simon Hare | | #46

    Thorsten - Shutters?
    Thorsten - Could you share a brief description of your shutter detail? We're developing custom thermal/aesthetic shutters for a project in a "neighborhood design district" in Boston to satisfy both history buffs and us energy geeks. Always eager to read about others' experiences with shutters in cold climates, and especially on cost and construction side of things. (I grew up in the middle east, where thermal shutters are the norm).


  47. Mark Klein Gimme Shelter | | #47

    Shutters/ windows
    Thorsten I look forward to hearing more about your local window initiative, also your shutter report, we have found that nicely finished shutters or insulated shades that work add a lot to our window cost. That reality is one of the things that has pushed us in the direction of more aggressive use of active solar thermal systems.

  48. Jesse Thompson | | #48

    Local Doors & Windows
    This local small door & window manufacturing facility you described, Thorsten, seems to be a big cultural gap between the EU and US, but one that could easily be bridged by innovative small manufacturers. We're far too dependent on the big national companies changing their offerings, but cold climate windows are such a small market in their mind, it's just not happening.

    I get the sense there is a world of small scale digital milling machines out there that would enable a smart & small wood based facility to turn out extremely sophisticated windows and doors:

    This would shift the embodied energy in the direction it needs to go. Glazing would be produced nationally, windows locally. Who wants to start the first one in New England for us?

  49. GBA Editor
    Martin Holladay | | #49

    Response to Jesse
    Then there's the issue of glazing. Mike Eliason wrote, "For our projects, the glazing has to be just right. Thermotech's 322 gain and Cardinal's LoE179#2#5 has less VT, and a much lower U-value than the Glastroesch."

    When I've researched the topic, I've gotten conflicting answers. Pinning information down is tricky because window testing standards in Europe differ from those in the U.S. Here's what I want to know: why can't Cardinal and Pilkington produce and sell better glazing to North American manufacturers, so that Thermotech can match the performance achieved by European window manufacturers?

  50. Jesse Thompson | | #50

    Personally, I'd be quite happy if we could purchase a locally made (250 mile radius?) wood window with a thermally broken frame and thicker than 3/4" glazing units with glass from Cardinal and Pilkington.

    Glastroesch might be a notch better than US glazings, but it's the good wood frames (better than 0.15 U frame or so) that are the weak link for us, not the glazing.

  51. homedesign | | #51

    German Wood Window frames
    The cross sectional illustrations of the German window frames are very interesting.
    They have a very elegant Architecture.
    The voids and thermal breaks appear to be very "engineered" and sophisticated.
    The same can be said for their high performance doors and frames.

  52. Michael T Heffron | | #52

    Exhaust fan ventilation
    In the systems you have seen using a small exhaust fan for ventilation are they also using some sort of through wall damper to provide the make up air? It seems that would be a necessity if you have a very air tight envelope. (Here in Washington state it is actually required by code no matter how leaky you building is.)

  53. GBA Editor
    Martin Holladay | | #53

    Response to Michael Heffron
    I've seen successful exhaust ventilation systems with and without passive air inlets.

    As I'm sure you know, the volume of incoming makeup air is always the same as the volume of the exhaust air. It's possible to measure the performance of an exhaust fan when the home is being commissioned. If your design calls for a 60 cfm exhaust fan, just test the airflow of the fan. If the fan is exhausting 60 cfm, it's working. That means that 60 cfm of makeup air is finding its way into the home through random envelope cracks.

    If the house is so tight that a 60 cfm fan won't work -- an unlikely scenario -- you could always drill a hole in a bedroom wall. But I'd test the fan first.

  54. Alan Van Zuuk | | #54

    Heating/ventilation system costs posted seem unrealistically low
    Working with a small footprint, irregularly-shaped Passive House design our design team has been constrained in some of our equipment choices, and the owners very reasonably want excellent ventilation and no heat pump for the time being. So we chose a fully ducted Zehnder CA200 with factory pre-heat and WarmFlow post heater with a few electric resistance heaters to dry towels and backstop the post-heater. We are also pre-wired for any future split ductless unit.

    Reading Passive House articles and discussions makes me wish I lived somewhere over the rainbow where you can properly install an HRV for even $3K, or a radiant heating system of any description for less than $10K: We will pay $2500 for the CA200 HRV, including shipping. (Using a high performance Canadian HRV or Ultimate Air DX200 would save us about $500 after accounting for the pre-heater.) Add the post heater and either steel ductwork sealed with mastic, or the Zehnder proprietary HDPE flex ductwork, controls, registers, and filters and you have at least $5K in equipment, parts, and materials before any markups. Now add labor, and you end up in $7K territory with no margins whatsoever. A local HVAC contractor recently submitted an $18,000 bid for a fully ducted Zehnder CA350/steel/mastic/post heat system for a 2500 sq. ft. high performance home with a 12KBTU heating load. This HRV duct system has a pretty simple 8" supply plenum run straight through second floor I-joists. The electric resistance heaters to back up the low ventilation airflow in cold weather are $3K extra!

    Even though space conditioning needs are minimized by any tight, high-R envelope, we still have to provide ventilation at a rate that meets ASHRAE 62.2, 2007. In these super-tight envelopes we add the default ventilation credit CFM back into the ventilation calculations; at 50 CFM50 in 1400 sq. ft. the envelope will not provide any ventilation on its own. We use the Canadian Code as a design model and provide fresh air to every living space and exhaust from all bathrooms and the kitchen area, and attend to zonal pressure relief. The materials used to construct the system are important. The ubiquitous flex duct is not on the menu, as my experience testing and inspecting existing heating systems demonstrates American flex duct to be a temporary, poorly installed, high fan energy use duct material. There are few acceptable shortcuts in ventilating a Passive House.

    Doing HVAC justice in a Passive House or any high performance envelope is not the inconsequential expense it is often posed to be. Perhaps we are too accustomed to the initial costs of the common and inadequate 80%gas furnace/flex duct forced air systems that are such a liability in any house. It makes no sense to me to pretend we can deduct or even minimize the cost of a heating system in the light of these fundamental quality and design requirements.

  55. GBA Editor
    Martin Holladay | | #55

    Response to Alan Van Zuuk
    I really appreciate your real-world perspective and experience with actual costs. You confirm my belief that adhering to the Passivhaus standard does not yet result in HVAC equipment savings.

    Perhaps that day will come, but I doubt it. In the meantime, I still seek out and report on innovative builders who are building superinsulated houses with low equipment costs and low energy bills. They're out there -- but they're usually not adhering to the Passivhaus standard. Again, thanks

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