Does Your Job Require You to Choose or Spec Windows? We Want to Hear From You!

Michael FrancoIn this week’s blog post, Phius Product Certification Manager Michael Franco breaks down the challenges of choosing the right windows for passive house projects and invites you to our upcoming roundtable event to discuss what data points are most important when selecting windows.

A sample color infrared result from LBNL THERM software. This software tool allows practitioners to model 2D heat transfer between building components (in this case, how a window frame, its spacer, and glazing package interact as seen via a cross-section at the sill area). The left-hand side of the image represents the outside-facing portion of the window, while the right-hand side is the indoor portion. For the purposes of this visualization, red is warm, purple is cold. Heat is shown moving through this window assembly in the direction of red to purple (from inside the building toward the outside area).

A sample color infrared result from LBNL THERM software. This software tool allows practitioners to model 2D heat transfer between building components (in this case, how a window frame, its spacer, and glazing package interact as seen via a cross-section at the sill area). The left-hand side of the image represents the outside-facing portion of the window, while the right-hand side is the indoor portion. For the purposes of this visualization, red is warm, purple is cold. Heat is shown moving through this window assembly in the direction of red to purple (from inside the building toward the outside area).

Windows are critical to the function of any building, especially a passive one. We as building occupants and passive building practitioners have come to expect a lot from these transparent feats of engineering.

Our windows must let in light, but also the right amount of heat from the sun. Depending on the climate of residence, the “right amount of heat” may be as little as possible. Windows in climates with long cooling seasons are often asked to reflect a significant portion of the heat that is packaged together with the sunlight we need.

We also expect windows and doors to keep outside air outside, except for when we change our minds, enter, or leave the building. Whether they swing, slide, tilt or turn, these operable envelope components must find a way to properly seal against outside air. On top of this task, windows and doors must mitigate energy losses via thermal bridging despite their often more complex frame profiles – quite a tall order since we cannot sacrifice outside air or egress on demand.

All of these considerations factor into performance. For example, in order to meet the demands of a passive building energy model, a CPHC
® (Phius Certified Passive House Consultant) or energy modeler must understand a window’s thermal performance at the component level. To accurately predict how a fenestration product will perform, the practitioner needs specific thermal performance values for the product’s frame, spacer, and glass in order to calculate how much heat will escape annually via the glass itself and the contact points between the wall, frame, spacer, and glass when the product is installed at actual size.

This requirement is why center-of-glass performance values alone or whole-window performance values at a standard size are insufficient to understand a window’s thermal performance in an actual product. A window’s performance does not scale simply or linearly if someone were to take a whole-window performance value at a standard size and attempt to scale it up or down to the size their project requires. The ratio of frame to glass heavily affects a product’s performance, and it’s not possible to accurately measure the change in performance from standard size to actual size without component-level data.

Passive building practitioners are acutely aware of all of the above requirements (and more), as they navigate a sea of data to find windows, doors, and skylights that are the right fit for their project. Fortunately, Phius Certified Windows contain all the component-level data necessary to properly model the thermal performance of a window, door or skylight.

Here is where Phius would like to contribute even further – we plan to release an all new, updated version of our Certified Window Database that offers a robust, easily-navigable list of Phius Certified windows. The goal for this database is to offer practitioners these key features:

  • Photo by Max Lapthorne during a tour of the 425 Grand Concourse project

    Photo by Max Lapthorne during a tour of the 425 Grand Concourse project

    A comprehensive list of Phius Certified windows

  • Data critical to energy modeling and building performance for each Phius Certified window
  • Searching, sorting, and filtering the database to find the right Phius Certified window for a job

While we at Phius think we have a good understanding of what window data is important to passive building practitioners, we also want to make sure that what we produce will be as useful as possible to the community. In order to ensure that we create a worthy tool, we humbly ask that you help us help you.

Are you a CPHC, architect, or engineer? Do you regularly source or model windows for projects? We would love to hear from you. Your input will help us ascertain which data practitioners consider most critical in their search for windows, doors, and skylights.
Please join us for a focus group on Jan. 11 hosted by the Phius Product Certification team (Michael Franco and Graham Wright) and help us understand what you need to find the right transparent envelope components for your projects. Please RSVP here via this link. If you have questions or cannot attend the focus group on the date above and would still like to offer input, email Michael Franco (

Window comfort and condensation


Graham Wright

Graham Wright

At the 10th Annual North American Passive House conference in Chicago, Steven Bluestone and PHIUS’ Lisa White made a presentation about the design of the Beach Green North (BGN) project in New York City, a seven-story multifamily residential building of some 94,000 square feet and 100+ dwelling units. The design featured double-pane windows with R-5 glass and R-4 frames.

A number of people were surprised that R-7 triple pane windows were not in the design. Low performance windows can indeed lead to comfort and condensation problems, and we did look into that. Here, PHIUS Senior Scientist Graham Wright posts about window comfort and condensation, both for the BGN project itself and how that may inform the PHIUS certification protocol going forward.


Performance of building components such as windows has not been in the category of “hard-and-fast” requirements for certification. The hard requirements have been on overall building performance – the “three pillars” of space conditioning loads, primary energy, and air-tightness.

Though we have been adding more requirements over time, window performance has remained in the category of recommendation, not requirement. Since 2013 we have been recommending window performance by climate according to this table. You can see that for zone 4A, we are indeed recommending an R-7 window.

To be a bit more granular about it, New York (LaGuardia climate) has 12-h mean minimum temperature of 6.44 F, which would require a window U-value < 0.16 Btu/h.ft2.F or R-6.3, to maintain interior window surface temperature of 60.8 F (within 4 C of a 68 F air temperature, assuming an interior surface film resistance of 0.74 h.ft2.F/Btu.)

In terms of comfort, the first line of defense is the limit on peak heating load. Window U-value has a strong effect on peak heating load and, as explained in the report on the standard-setting process for PHIUS+ 2015 , we now require that projects meet limits on both annual heating demand and peak heating load (same for cooling). Moreover, the model building used in the standard-setting studies had its window U-values constrained so as to maintain 60 F interior surface temperature under winter design conditions (12-hour mean minimum outside temperature).

Thus the peak heat load criterion for the building overall is predicated upon windows that good, and it serves as an indirect curb on bad windows, while allowing the designer some flexibility to meet the overall peak load in different ways.

That is working well for buildings that are not tremendously larger than the study building. But BGN is fifty times larger, in terms of floor area. In the standard-setting report, we anticipated that there would be consequences of applying the same energy-per-floor-area criteria to all sizes of buildings; that is, larger buildings with lower surface-to-volume ratio (or surface-area-to-floor-area ratio) would more easily meet the criteria. We opted for giving this allowance to larger residential buildings, because such forms of housing are more efficient in terms of their materials usage or embodied energy.

Because of that large-building break, the BGN design could meet the peak heat load criterion with windows as low as R-2.5. The best double-pane windows available are in the R-4 to 5 range and the team asked if those would be acceptable. So we did some additional calculations on comfort and condensation.

Comfort analysis

The comfort analysis was done largely using the ASHRAE Comfort Tool, a standalone software that allows you to put an occupant in a room, then compute the radiant and operative temperatures and the human comfort metrics Predicted Mean Vote and Predicted Percent Dissatisfied (PMV and PPD).

The comfort standards ISO 7730 and ASHRAE 55 are in agreement on fundamentals. Their development was coordinated and they share the same models for the PMV and PPD metrics for overall bodily comfort, as well as “local” discomfort on different parts of the body. ISO 7730 is focused on analysis and assessment methods. ASHRAE 55 draws pass/fail lines whereas ISO 7730 just makes recommendations; it sets up categories A, B, C of design criteria for consideration.  The ASHRAE 55 pass/fail lines correspond to ISO 7730 category B. In terms of overall body comfort, the criterion is less than 10% dissatisfied. (Even at a predicted mean vote of zero, that is, on average feeling neither warm nor cool, there are still 5% of people dissatisfied.)

Worth noting is that our protocol of modeling buildings with a heating setpoint of 68 F already pushes the winter comfort to the cool end of the acceptable range of Category B or ASHRAE 55, even if there are no windows in the room at all. The clothing and activity level of the occupants are factors in the PMV, but even with Clo=1 (long sleeves and sweater) and a little activity of Met=1.1 (seated, typing), in order to get a PMV near zero you need an operative temperature of around 22 C (71-72 F). The Building America default heating setpoint happens to be 71 F.

At 45% relative humidity (RH) and an operative temperature of 68 F, the PMV is minus 0.6 and the PPD is 12%. Because the operative temperature is approximately the average of the air temperature and the mean radiant temperature, it will be lower than the air temperature in the winter when the window surfaces are colder than the walls. Thus, under the scenario shown in the first column of Table 1, the lower setpoint for air temperature has used up the design margin for comfort, leaving none for windows. If the activity level is a little higher but the RH is a little lower, as in the third column, then there is some comfort latitude remaining to accommodate windows.

Table 1. Winter comfort at two heating setpoints.

Air temp F





Radiant temp F





RH %





Air vel ft/min

























There are two ways to look at this

One is that, under our current recommended way of modeling things, the improved comfort that high performance windows would bring is taken back with the lower heating set point, traded to save energy.

Another way to look at it is that as a general point, really good windows really are required for comfort at a 68 F heating setpoint.

However, to use this type of analysis to derive an absolute minimum window surface temperature criterion from the comfort standards, it would have to be carefully contrived to allow any windows at all. One would have to be specific about the activity and clothing and activity level of the occupants at least in an average sense, and small differences could make the difference between say, an 8 F margin between the window surface and the air, to no margin at all.

For the BGN window comfort analysis we instead performed a relative comparison, first constructing a baseline scenario wherein the occupant comfort was close to neutral with no windows, and then adding windows and checking the difference in comfort.

Typical main-room dimensions for the Beach Green North project are 10 x 22 feet. There are corner rooms with one window on each of the two exterior walls. Windows are 3’ 3” wide and 5’ 2” tall. Geometrically, an occupant in the corner with the windows also near the corner would feel the greatest comfort impact.


Baseline scenario (See Figure 1):

Occupant is seated, quiet (1.0 met), typical winter clothing ensemble (0.9 clo). Air temperature and radiant temperature both 74 F, humidity ratio 0.010.

Comfort is almost exactly neutral: PMV -0.10, PPD 5%

Figure 1. Baseline comfort scenario



Windows scenario (See Figure 2 and 3):

Room 22 x 10 x 8 feet. Occupant seated in corner 3.3 feet from each wall, facing the short wall. Window jambs are 2 feet from the corner on each side. Window inside surface temperature is 50 F, corresponding to window U=0.4 at 6.44 F outside.

Mean radiant temperature drops to 71.2 F. PMV drops to -0.30 and PPD increases to 7%. This is still within the ASHRAE 55 or Category B criteria range of PMV +/- 0.5 and PPD < 10%.

Figure 2. Mean Radiant temperature with windows in the corner at 50 F.


Figure 3. Overall comfort in window scenario, shifts PMV 0.2 cooler.Figure3


Going from no windows to U=0.4 windows caused the PMV to shift cooler by 0.2, and the PPD to increase from 5% to 7%.

There is also local discomfort to consider. Even if the whole wall was at 50 F, this would still be just within the acceptable range for cool-wall radiant asymmetry.

We communicated to the BGN team that windows up to U=0.29 would be acceptable, splitting the difference between U=0.18 and U=0.4 (figuring that the shift in PMV would be even less going from U=0.14 to U=0.29 than it would be going from no windows to U=0.4.)

One of the other benefits of keeping the window surface temperature up within 3 or 4C of the air temperature is that there is less pooling of cold air under the window, and no need for heat under the window to prevent discomfort due to head-to-foot temperature difference. Some loss of amenity is occurring in this respect, but we did not attempt to quantify it.

One interesting point is that head-to-foot is indeed one of the local discomfort criteria in both ISO 7730 and ASHRAE 55 (per clause but, in ASHRAE 55, none of the local discomfort criteria apply unless the occupants are at Clo<0.7 AND Met<1.3. With that low of a clothing level, they would not be overall comfortable at 20 C (68 F) air temperature anyway, so likely they are bundled up to 1.0 Clo and the local discomfort isn’t as important.

Anecdotal feedback has been mixed. Our Canadian friends tell us “no one is complaining about comfort here with R-6 windows” even where we would recommend R-8. Our Lithuanian colleagues say “double-panes are uncomfortable; no one uses double-panes in Lithuania.” Lithuania is 10 F colder than NYC though, with a 12-hr mean minimum temperature of 3.8 F below zero versus LaGuardia at +6.4 F.

As to the certification program going forward, the matter was brought before the full PHIUS Technical Committee at our October meeting,

For the time being, the Committee decided to refrain from imposing a “hard requirement” on inside surface temperature for winter comfort, or directly on window U-value, and to continue in the category of recommendation.

We have already collected the data to set recommended winter-comfort-based U-value maximums for all the climate locations on our criteria map, and could make those show up.

A possible approach for certification could be to require that those recommendations are followed but give an option to do a more detailed comfort assessment like the one shown above.  This very kind of material-cost versus analysis-cost tradeoff is done elsewhere in the program, for example with thermal bridges. One can do a conservative design following simple rules , or make an edgier design and do more engineering work to verify whether it meets criteria.   Such an approach would require the development of some additional calculation protocol.

Condensation analysis: Background

One of the “hard requirements” PHIUS has added pertains to avoiding mold growth on interior surfaces caused by thermal bridges. Even if a thermal bridge is tolerable in terms its impact on the space conditioning loads and demands, it is not tolerable if it can lead to mold growth on the inside. Our protocol follows ISO 13788, and one of our calculator tools follows its methods. Just as in calculating the energy impact of a thermal bridge, we make a THERM model of the detail. But instead of calculating the extra energy loss, the critical result is the point of lowest temperature on the inside surface, and the criterion is that at that point, the interior air, when chilled down to that temperature, should be at less than 80% relative humidity.

ISO 13788 addresses how to determine the appropriate boundary conditions – the outside temperature and the indoor relative humidity. This is based on consideration of the monthly average outside temperature and humidity for the climate. The outdoor humidity is added to an indoor source that depends on one of five building humidity classes from low to high.

For each month, a psychometric calculation is then done to determine a minimum inside surface temperature needed to keep the RH at the surface below 80%.

The critical month is the one in which that minimum surface temperature is farthest from the outside temperature and closest to the inside temperature, because that requires the detail to be the most “insulating.” This “surface temperature factor” (fRsi) of the building element is defined mathematically as

fRsi = (inside surface temp – outside temp)/(inside temp – outside temp),

with a surface resistance at the inside surface of Rsi.

(Usually the critical month is also the coldest month but not always – depending on the climate it might be in October, for example)

ISO 13788 also addresses assessment of condensation on “low thermal inertia” elements such as windows and doors, using a similar procedure, but with some differences: instead of keeping the RH below 80%, the goal is to avoid outright condensation (RH=100%), because windows and doors have impermeable surfaces that aren’t as subject to mold, but vulnerable to rot and corrosion if outright wet. But the outside design temperature is more severe – instead of a monthly average, it calls for the lowest daily mean temperature of the whole year.

For our BGN analysis, we:

1. Used the 13788 procedure for “low thermal inertia” elements to determine the required minimum surface temperature and fRsi to avoid condensation.

With an interior RH of 48% in the coldest month, the dew point of the interior air was 47.7 F, so the inside surface must be warmer than that.

2. We then did a one-dimensional calculation with the frame U-value at 0.28 to determine if that was the case. Instead of the lowest daily mean temperature, we used (for convenience) the ASHRAE 99.6% design temperature, as AAMA does for their Condensation Resistance Factor. This was 13.8 F.

With an interior temperature of 68 F, and an inside film resistance of 0.74 h.ft2.F/Btu, the inside surface temperature then is 68-(0.29*0.74)*(68-13.8) = 56.7 F, that is, 9 degrees above the dew point.

Of course, this does ignore the fact that the surface temperature could be lower right in the corner where the frame meets the glass, because of the conductivity of the spacer, but 9 F provides a comfortable margin. ISO 13788 does caution that one-dimensional calculations aren’t generally good enough, but it is a place to start. We will refine the “low thermal inertia” version of our 13788 calculator and publish that soon.

We’ve also been asked whether we can specify an NFRC Condensation Resistance rating (CR). The AAMA recently published a good summary paper [AAMA CRS-15] that explains the differences between NFRC’s Condensation Resistance (CR), AAMA’s Condensation Resistance Factor (CRF), and the Canadian temperature Index or I-value, per CSA A440.2.  All of these are 0-100% higher-is-better ratings, but they are not directly comparable to each other.

From that paper it is clear that the CRF and the I-value are the same kind of thing as what ISO 13788 calls fRsi – ratios that indicate how far some critical inside surface temperature is towards the inside air temperature. Therefore, if that data is available for a window of interest, those ratings could be compared directly to the required fRsi from a 13788 calculation for “low thermal inertia elements” for an indication as to whether a window is good enough in the climate location of interest.

The AAMA white paper indicates that the I-value is generally more conservative/stringent than the CRF due to differences in the temperature sensor placements. Both of these are physical tests.

AAMA provides an online calculator that takes a given outdoor temperature, indoor temperature, and relative humidity, and computes the dew point and the required CRF, so it is making the same kind of calculation as called for in ISO 13788. (The disclaimer for it makes many good points.)

The NFRC Condensation Resistance rating is more complicated and harder to interpret, except as a relative ranking. It is basically the percentage of the window frame, glass, or edge-of-glass area (whichever is worst) that is below dew point under the standard test condition temperatures, averaged over interior RH levels of 30, 50, and 70%. It is based on modeling rather than a physical test.

At the October Technical Committee meeting there was consensus on the general matter of setting a definite requirement to avoid condensation on windows.

The next issues then are: under what circumstances a window condensation check should be required in project certification, and what the passing criterion should be.

PHIUS’ Certification staff are working out those details and plan to phase in the requirement.

In the meantime, a determination about “when to check” should key on risk factors such as:

  • Window U-value significantly above the comfort requirement.
  • Frame U-value significantly above the glass U-value.
  • Presence of aluminum spacers.
  • Lo-e coating on the inside surface of the glass.

Our recommended passing criterion is that 1-D calculations on the surface temperatures or fRsi of the frame and the glass, or an AAMA CRF rating, should meet the ISO 13788 minimums at the ASHRAE 99.6 design temperature for the climate, with some safety margin, or that a CSA I-value meets it without a safety margin.

We will also consider adding to our window rating data the fRsi calculated at the worst-case location, the inside corner where the glass meets the frame.


PHIUS Certified Data for Windows program online

Graham Wright, who heads up the PHIUS Certified Data for Windows program, joins us today to provide clarifications on some key features of the program. And to clear up some misinformation.

I get and see online a lot of questions about the PHIUS Certified Data for Windows program, and how it differs from PHI’s Euro-centric program. Apologies—it’s clear that we haven’t communicated the program as well as we should have—but we are catching up to ourselves.

I’m happy to report that we’ve got data and climate recommendations for a nice range of windows online here.

The table lists products, climate zone recommendations, full data certificates and supporting THERM files.

There are a lot more coming—and we’ll be converting this static table to an online database soon.

For manufacturers and suppliers, we invite you to download a detailed description of the certification process (with an application form), and the document is also available at the program overview page.

In the meantime, I hope to clear up misconceptions and concerns about the program:

I heard that the PHIUS Certified Data for Windows program doesn’t account for whole-window R-value. Is that correct?

In fact, the program does provide recommendations based on whole-window R-value, and all have the force of criteria as far as manufacturers are concerned. Also the program provides recommendations / criteria on solar heat gain coefficient.  (They vary by climate from about R-5 to R-9.)

Why doesn’t the program address surface temperature factor (“fRsi”)?

Eventually, it probably will – but on the list of important future program improvements for North America, it’s pretty far down the list, after data publication, NFRC harmonization, air-tightness-durability, and Canadian Energy Rating. That’s partly because fRsi isn’t pertinent to hot climates (and there’s a lot of hot climate zone in North America), and we decided to pay more attention to solar heat gain coefficient.

We cover the condensation / fRsi issue by providing the THERM files, which allow consultants to calculate it if they wish, and more precisely, with respect to the expected interior humidity conditions for their particular project and climate. (I made an ASHRAE 160 + ISO 13788 calculator for computing fRsi requirements climate- and project- specifically. We make it available during CPHC training, and if you email me at, I’ll be happy to send it to you.)

Moreover, both the fRsi criterion and the single-height bar on U-value (at about R-7) look to be legacies of the single-zone origin of PHI’s window program.

Setting that high bar at R-7 has certainly spurred innovation. But our multi-zone system does the same thing – people want to “level up” from zone 3 to 4 or from 4 to 5.  A single standard, when it comes to windows, fails to inform a shopper whether a window is appropriate for a passive house project because it’s overkill in some places and under kill in others.

It also hurts manufacturers—many of them mainstream producers of very affordable windows—who, right now, offer windows that will work well in mild climates. Designers, builders and clients should have those options.

Moreover, we find much to admire in the NFRC system and would like to get the best of both worlds. Funding for such harmonization work is being applied for.

Do we really need the PHIUS window program?


PHIUS’ window program is moving toward a critical goal: producing data in the format that passive house consultants need, and that enables direct comparison to windows rated by other EN-based outfits like PHI or say, IFT Rosenheim. Both window industry representatives and passive designers have told us this is critical if we want to energize the market. To be sure, the programs’ fundamentals are aligned, but the presentation and recommendation level is different in a number of ways. For example, PHIUS’ program is more fussy about solar heat gain and zone granularity. PHI’s is more fussy about horizontal / vertical.

At PHIUS we believe that passive house principles apply universally, but a single criterion does not. From their Greenbuild presentation, it was clear to me that PHI recognizes the need for climate-specific recommendations for components, including windows.  But as I understand it their window certification is still pass/fail at one level. PHIUS has moved more quickly on this front. Going forward, if you hear “this is a passive house window” people should know to ask:  for what climate?  Be wary of claims about passive house windows that don’t show any numbers or label or certificate, it might just be loose talk.

Why such a long name? Why not just PHIUS Certified Window, for example

We settled on the name with care. The AAMA or NFRC would say, you don’t have a “window certification program” unless you address air / water / structural issues. So PHIUS is not certifying windows (and neither does PHI by such lights).

We’re certifying certain data about windows, namely thermal performance, modeled. Hence, “PHIUS Certified Data for Window Performance Program.”

We did not include the term “passive house” because while designed with passive house in mind, the data—even for windows that don’t receive recommendations for passive application—will be extremely useful for designers.

Certified Passive House Consultant Training in the North American Context: Then, Now, and Moving forward

The mark of a CPHC...

In May 2008, PHIUS launched the first English-language passive house training program, and with it, the Certified Passive House Consultant (CPHCsm) accreditation.

By the start of 2012, nearly 700 professionals had completed or were enrolled in the PHIUS training program. More than 300 trainees from across the nation had passed the exam to become accredited as a CPHC. And they’ve been busy – they’ve submitted more than 150 projects — residential, commercial and retrofits– for verification in the PHIUS+ Quality Assurance program.

From the beginning, PHIUS classes had a North American accent that was based on real-world

Louisville Courier-Journal article from 1982 detailing a house built in Urbana that utilized superinsulation, airtight envelope, energy recover ventilation, and solar gains. Yes, 1982.

experience.  In 2008, that experience was largely my own and that of a handful pioneering souls, including many who had pioneered passive house principles like superinsulation in the United States and in Canada decades ago.

That’s changed, thanks to lots of committed individuals. Leading these trainings has been a revelation — and an inspiration — for me and my fellow instructors. Our classes are filled with enthusiastic, extremely bright and energetic architects, engineers, builders, energy raters and consultants. Everyone gets – and gets excited by — the fundamental passive house principles. Everyone brings their real-world experience from their regions.  And everyone contributes to advancing passive house.

The result: A continually evolving training curriculum that draws on years of experience and data from a growing community with local expertise.

For example: We’ve learned that hygrothermal modeling – maybe unnecessary in some climates – is critical to successful passive house design in many North American regions. It’s the only way to anticipate and address moisture issues in envelope components associated with humidity that are widely present in the United States and Canada. As a result, students now get a hands-on introduction to hygrothermal modeling using WUFI modeling software. (A free version of WUFI is offered by Oak Ridge National Laboratory and Fraunhofer Institute.)

Similarly, THERM (free download from Lawrence Berkeley Laboratory) is useful to calculate thermal bridging, and students now receive an introduction to using that software tool. Because WUFI and THERM have become de rigeur in many scenarios, we’ve also developed workshops devoted entirely to those tools.

Click on the image to download the PHIUS Technical Committee's paper on evaluating windows for passive house.

The field is developing quickly, and the curriculum will develop accordingly. The existing community of CPHCs continues to build and certify projects and their experience flows back into CPHC classes. The PHIUS Technical Committee, comprising leading passive house practitioners, regularly publishes papers – the latest on evaluating window performance for passive house projects. This year, PHIUS will publish the PHIUS library, a training companion folder that will be updated on and ongoing basis as sections are revised or added (Passive House Alliance members benefit from receiving the newest updates as part of their membership benefit packet for free!).

As our curriculum has evolved, so has the examination process: A computer-based exam component focuses exclusively on North American climates, detailing, construction technology, building conventions, climate-appropriate mechanical equipment and code requirements. Americans can work in Inch Pound units and Canadians can choose metric. Examinees then take home a basic design exercise. This year, for the first time students can opt to take the exam on the afternoon of the last day of class. If students don’t feel ready, they can opt to take the exam at the end of any class program at any location at a later time. The Passive House Alliance US (PHAUS) is also hosting two exams per year in various chapter locations scheduled independently from trainings.

European training providers also offer Certified Passivhaus Designer (CEPH) training in the North American market – CEPH standing for Certified European Passive House. For those who take the European training or have achieved the European accreditation, PHIUS will soon offer an abbreviated training and exam sequence to receive PHIUS CPHC accreditation and listing on the PHIUS Web site.

Join us!

PHIUS has an incredible roster of instructors from around the country. But the buzz in the CPHC training classrooms comes as much from our students as us. (If you want to hear from someone who took the class, check out Jesse Thompson’s account of taking the class on the Green Architects’ Lounge podcast.)

We’ve come this far as a community, and we need to grow the community of qualified passive house professionals if we’re going to achieve the goal of making passive house mainstream. There are more opportunities than ever, as PHAUS chapters begin offering training in their regions, and as partners like Earth Advantage Institute and Carnegie Mellon University begin hosting classes.

Upcoming CPHC trainings include: San Francisco later this month; Salt Lake City in May; June brings New York, Atlanta (in partnership with the local PHA-US chapter) and Portland (through our new partner, Earth Advantage Institute). Seattle training dates, also offered by Earth Advantage, will be announced soon. Boston dates are also in the works.

Check the schedule for updates at the PHIUS site or at the PHAUS National Events calendar.

If none of the sites/dates work, subscribe to the PHIUS newsletter to get updates on additional training sites and updates.

And you can read a full course description here.

See you soon I hope!




One-Stop Passive House Shopping: Join Me at NESEA’s BE12 Trade Show

I’ll continue with the climate-focused case studies from the last installment soon. Right now, though, it’s worth giving a headsup on an upcoming conference event.

In the early days of Passive House in the United States, finding Passive House components – windows, HRVs, etc. – was a project in itself. How far we’ve come! In fact, if you’re interested in building your Passive Dream House, you’ll be able to find everything you need on the floor of the NESEA Building Energy 12 trade show floor.

The national conference of the venerable Northeast Sustainable Energy Association, every year BE12 astonishes. This year in Boston will be no different.

Passive House has been at the forefront of recent NESEA conferences. This year, to meet the growing appetite for all things Passive House, NESEA asked me to lead a tour of Passive House products that will be displayed at the NESEA trade show. (You’ll need to sign up for my Tuesday workshop to join the tour.) And so it will be my pleasure to guide the tour, to introduce them to the forward-thinking folks who’ve made available awesomely performing materials and components to the designers, builders and homeowners of Passive Houses. And made the components cost effective.

Some suppliers have been there for decades: Pioneers such as Stephen Thwaites with Thermotech Fiberglass Fenestration. I used Thermotech windows for the first time in the Smith House in Urbana, Ill. In 2002, it was the only North American window I could find that approached the Passive House specifications for the Urbana climate. Little did I know how dialed-in the window design by Stephen Thwaites really was. After 10 years of experience with Passive House construction throughout all different climate zones I have come to appreciate the smart balance applied in this design. A comparison of the energy balance of a certified European window and the Thermotech windows for my house showed that they were performing virtually equally, Thermotech maybe even a little better. How could that be at somewhat higher overall U-values? It is all about the right balance of Solar Heat Gain coefficient and U-value dialed into the specific climate conditions. Thinner frames to maximize the glass area in a high solar radiation climate is where the money is at. Passive House two thumbs up for an excellent North American manufactured fiberglass window perfectly designed for cold and sunny climates.

And then there is Pinnacle Window Solutions, with another classic, SeriousWindows. Serious has been used in many Passive Houses across the nation. It is a North American manufactured fiberglass window featuring excellent U-values well suited for cold and very cold climates. The solution of the suspended plastic film technology instead of an additional glass pane to increase the R-value allows the creation of a window that features essentially quadruple window performance, while maintaining a manageable weight. This is an interesting choice for the cold and very cold and perhaps more cloudy climates in North America. The high R of SeriousWindows comes at a price: the Solar Heat Gain Coefficient goes down the better the R and the visible transmittance is lowered as well. In cold climates with very good solar opportunities, a high Solar Heat Gain window with less R might perform just as well or better. This only reinforces what we have been teaching in the PHIUS trainings: the right window for the right climate. And Serious definitely has a place at the table.

In the last couple of years many entrepreneurs have brought new options for high-performance European Style windows. For example, Intus Windows has been turning heads with amazing Euro-style windows at very competitive prices (typically the Euro style window comes at a price). European Architectural Supply and New England Fenestration, LLC offer more European window varieties from other manufacturers such as Schueco, Macrowin and Unilux, all superb performing windows, all of them featuring thermally broken frames certified for the cool moderate climate through the Passivhaus Institut.

Still another excellent choice: Bieber Windows, and ZolaZola’s booth will be staffed by Passive House veterans Florian Speier and David Gano.

Go and visit — you have to see and touch these windows to understand the quality.

Windows are critical to Passive House construction, and so are systems components for minimized micro-load mechanical and ventilation systems. They put Passive House within economic reach. On this front, too, NESEA will also include many exhibitors. In addition, I’ll give a workshop at NESEA on Tuesday on cost effective integrated mechanical systems for North American climates.

In the early days, I would begin designing Passive House projects by first sketching the continuous air tightness layer. Later that focus shifted slightly toward laying out the mechanical system and the duct system. I am in love with Passive House mechanical systems simply because I never dreamed of being able to design it myself, and being able to really integrate it into the design process. They are in their own right very elegant and if well done one the key quality indicator of a Passive House. Hence, Passive House homeowners are actually proud to show off their mechanical rooms.

My latest interest has shifted towards heat pump hot water heaters as viable Passive House solutions, even in cold climates. Stiebel Eltron, Inc. makes such an appliance. It is a true super-insulated tank a Passive House enthusiast dreams of. Our Passive House builder, who installed it in our last project, was blown away in terms of efficiency and quality. By far the most energy efficient solution on the market, the unit is slightly more expensive than other options, but a good value. Another Passive House two thumbs up. Heat pump hot water heaters are becoming a very interesting solution for integrated mechanical systems designs for Passive Houses. Located inside the thermal envelop in a super low load home (including cooling and latent loads) the contributions to cooling and dehumidification by a heat pump hot water heater can be significantly helpful and in some cases all it takes.

And then there are the mini-split heat pumps. NESEA attracted two significant Passive House players, Daikin AC Americas, Inc. and Mitsubishi Electric HVAC. The mini-split systems are quickly becoming the most popular heating/cooling and dehumidification systems for Passive Homes. Daikin and Mitsubishi are among the manufacturers offering a heat pump slim duct built-in option. The units can be obtained in small sizes for single-zone and multi-zone systems (just what we need for Passive Homes) starting at 6k BTU/h and up. They generally have very good SEER ratings, the slim ducted options have a little lower rating, but are still solid in cold and mixed humid climates with larger cooling and dehumidification loads where integrating the space conditioning in the ventilation system is preferred.

Another interesting product from Daikin is the point source “Quaternity” Heat Pump wall mount unit. The SEER rating is 26.1 and it has an additional feature for warm humid climates where dehumidification might be needed when there is no cooling need: a dehumidification mode only. This unit is available in three capacities, 9k, 12k and 15k BTU/h. The Mitsubishi’s wall units have one of the best SEER ratings (26) and operate down to very low temperatures, making it appropriate for cold and very cold climates.

Mitsubishi has also truly excelled in terms of control of its heat pumps. Recently Mitsubishi introduced wireless technology eliminating the need to run wires and offering a centrally located thermostat just the way we like it.

Wagner Solar Inc and Tarm Biomass offer extremely low source energy heating options for multi-family Passive House projects (we are seeing more and more coming into the certification process). One major challenge of the multi-family typology is meeting the source energy criteria. Both companies sell wood and pellet boilers that offer excellent low carbon heating systems options. One boiler can be used for an entire medium-sized apartment complex if combined with Passive Solar. The Tarm Biomass boilers range from 75-80% efficiency for wood, 85-87% for pellets. Wagner Solar Inc offers a Pellet boiler with the efficiency of up to 93%. Smaller units for single family are available in Europe in combination with a hot water heat exchanger. It’s worth checking on availability of these systems. They are fine low source energy solutions for cold climates with predominantly heating requirements and lots of wood.

475 High Performance Building Supply is bridging the gap with many products not only in regards to air tightness but also over into the ventilation system realm. This Brooklyn, NY-based outfit has an interesting suite of specialty products mainly imported from Europe. They offer airtightness solutions from INTELLO plus and Pro Clima, a wood fiber sheathing/insulation product from Gutex, triple pane skylights from Fakro, and Foamglass from Pittsburgh Corning.  They offer a through-wall decentralized apartment venting solution with a ceramic heat recovery core from Lunos and a compact heat pump by a Swedish company Nilan (not available yet but in testing – coming by year-end according to 475). The configuration is cost effective for cities, as it saves a lot of space by comprising all the mechanical functions of a Passive House into one compact box the size of a refrigerator.

Another high performance ventilator on the NESEA floor is Zehnder America, Inc.; it’s still the only game in town on this show floor in terms of high efficiency heat recovery ventilation. As important as high efficiency heat recovery ventilation is to Passive Houses, we still hope for a little more competition and for the North American ventilation system manufacturers to come up to speed. In the  ventilation systems by Zehnder — integrated solutions for pre-warming the incoming air through ground source heat exchange and fast flex ducting systems – continue to impress. New this year: it received the Home Ventilation Institute Testing stamp of approval. The results show the heat recovery efficiency of this HRV under this testing protocol coming in second with 93% Apparent Sensible Effectiveness (ASE) which is topped by only one other ventilator made and sold in America, the UltimateAir RecoupeAerator with 95%. Zehnder products are a little pricy, but with the ease and time savings of installation and an impeccable maintenance record, it seems a well worth investment.

That’s it for part one of the tour…here’s part two, where we get into some more airtightness and wall system products.