A review of the three window certifications now available for window manufacturers on the US market. First issued in July, 2013 and updated on June 28th, 2015. This builds on a previous comparison I've done reviewing differences in testing protocols by PHI and NFRC.

1. NFRC vs. PHI vs. PHIUS
Window Certification
The full fruit basket?
Bronwyn Barry, Assoc. AIA., CPHD
Design Director - One Sky Homes
July 11, 2013
*Edited: June 29, 2015

2. Three window rating systems now on US
market:
Passive House Institute (PHI):
• International
• Climate-Specific Performance Req’d*
• Simulation only
Passive House Institute, US (PHIUS):
• US – based
• No Min. Performance Req’d
• Simulation only
National Fenestration Rating Council
(NFRC):
• North America based
• No minimum standards
• Simulation and Product Test Req’d

3. NFRC’s certification criteria:
Simulation:
1. Uwindow (required)
2. SHGC (required)
3. Air Leakage (optional)
4. Visible Light
Transmittance
(optional)
(No Min. Performance Req’d.)
Verification:
1. Destructive test of
window sample
2. Factory inspection
Image from NFRC website: http://nfrc.org/fenestrationfacts.aspx

4. PHI’s Certification Criteria:
3 Simulation Min. Requirements:
1. *Climate Specific
(Was: Uw </= 0.8
W/m2
K
(0.14 BTU/hrft2
F or 6.7 hrft2
F/BTU)
2. Uw installed </= 0.85 W/m2
K
3. fRsi </= 0.7
(Varies for other transparent components, including curtain
walls, roof domes and skylights. See document:
Certification criteria and calculation regulations Passive
House Suitable Transparent Components:
http://www.passiv.de/downloads/03_certification_criteria_tr
ansparent_components_en.pdf)
Image from PHI component database: http://www.passiv.de/komponentendatenbank/files/pdf/zertifikate/zd_northwin_vision_en.pdf

5. Simulation:
1. Uwindow (required)
2. SHGC (required)
3. Air Leakage (optional)
4. Visible Light
Transmittance
(optional)
(No Min. Performance Req’d.)
Image from PHIUS info document for window manufacturers – Graham Wright
PHIUS’s Data Certification Program:

6. How NFRC calc’s U-window:
(Ucog*Acog) + (Uf*Af) + (Uedge*Aedge)
Aw
Uw =
Ucog
Acog
Uf
Af
Ucog = U-value glass
Acog = Area glass
Uf = U-value frame
Af = Area frame
Uedge = U-value edge of glass
Aedge = Area edge of glass
Aw = Area Window
Uedge
Aedge
Thanks to Christian Kohler at LBNL for formula verification.
* NFRC requires specific IGU values for each window certification. The U-window value is
therefore specific to each certification and makes U-frame values difficult to extract for PHPP use.

7. NFRC Therm file protocols:
Ucog Boundary Condition:
Temp: 69.8 degF (21 degC)
Film Coeff: (Rs)
0.39 BTU/hr.ft2
F (2.19 W/m2
K)
(Defined using WINDOW)
Uedge Boundary Condition:
Temp: 69.8 degF (21 degC)
Film Coeff: 0.39 BTU/hr.ft2
F (2.1 W/m2
K)
Uf Boundary Condition:
Interior Wood/Vinyl Frame
Temp: 69.8 degF (21 degC)
Film Coeff: (Rs)
0.43 BTU/hr.ft2
F (2.44 W/m2
K)
Boundary Condition:
NFRC 100-2001 Exterior
Temp: -0.4 degF (-18degC)
Film Coeff: (Rs)
4.58 BTU/hr.ft2
F (26 W/m2
K)
Emmissivity: 0.84
U-factor Surface: Edge
U-factor Surface: Frame
U-factor Surface:
SHGC Exterior
(frame exterior only)

8. NFRC simulation sample results:
Ucog = 0.13 BTU/hrft2
F
Uw = 0.14 BTU/hrft2
F
SHGC = 0.38
VT = 0.51

9. Sample NFRC certificate:
Simulation:
1. Ufactor (whole window includes
frame + glass)
2. SHGC (specific to each IGU)
3. Visible Transmittance
4. Air Leakage (optional)
Verification:
NFRC certification requires
destructive testing of a
sample window and regular
factory inspections to
achieve full certification.
Image from NFRC website: http://nfrc.org/fenestrationfacts.aspx

10. How PHI calcs window U-value
For certification:
(Ug x Ag) + (Uf x Af) + (ψspacer x Lg)
Aw
Uw =
Ug
Ag
Uf
Af
Lg
Ug = U-value glass1
Ag = Area glass
Uf = U-value frame
Af = Area frame
Ψspacer = psi
L g = Length spacer
Aw = Area Window
ψspacer
1. It is important to note that PHI uses a ‘standard’ IGU rated at 0.123 Btu/hr.ft2F, or 0.7 W/m2K, for all their
certification simulations. This generates a U-window (frame + glass) output value, but allows for easy
comparison of U-frame values between multiple window profiles. Specific U-glass values are calculated
elsewhere in the PHPP for project-specific performance calculation.
2. *Reference Glazing Values are now specific to each Climate Certification. (See chart on Slide #x)

11. *Uf Boundary Condition:
Temp: 68 degF (20 degC)
Film Coeff: (Rs)
1.35 BTU/hr.ft2
F (7.67 W/m2
K)
PHI Therm file protocols:
*Ug Boundary Condition:
Temp: 68 degF (20 degC)
Film Coeff: (Rs)
1.35 BTU/hr.ft2
F or 0.74 hr.ft2
F/BTU
(7.67 W/m2
K)
*Boundary Condition:
Temp: 14 degF (-10degC)
Film Coeff: (Rs)
4.35 BTU/hr.ft2
F
or 0.23 hr.ft2
F/BTU
(24.69 W/m2
K)
U-factor Surface: Interior
U-factor Surface: Frame
U-factor Surface: none
(This page verified by Passive House Academy)
*Values are now vary for each Climate Certification. (See chart on Slide #15)

12. *Exterior
Boundary Condition:
Temp: 23 degF (-5degC)
Film Coeff: (Rs)
4.35 BTU/hr.ft2
F
(24.7 W/m2
K)
*Interior
Boundary Condition:
Temp: 68 degF (20 degC)
Film Coeff: (Rs)
1.42 BTU/hr.ft2
F (4 W/m2
K)
PHI also calculates fRsi*:
(Cursor placed at inside edge
of glass and frame)
(This page PHI verified: Benjamin Krick 7.25.13.)
*Values are now vary for each Climate Certification. (See chart on Slide #15)

13. Uw-installed =
• Interior Surface temp difference
allowed = 4.2K max.
• θopK = operative temperature
(average temp of interior room
surfaces and interior air
temperature.)
• θaK = (not clear to author at this
time – requires PHI verification)
And Uw – Installed:
* This page PHI verified: Benjamin Krick 7.25.13.
(Ug*Ag) + (Uf*Af) + (ψedge*Lg) + (ψinstall*Lf)
Aw

14. What is fRsi and Uw, installed ?
Passive House Certification is essentially a
DURABILITY and COMFORT standard.
By including requirements for Uw, installed and fRsi, PHI
certification checks against interior drafts and interior
surface condensation. This ensures a high level of
occupant comfort and the elimination of mold growth.
Got Mold?
Info from PHI component Certification Criteria document: http://www.passiv.de/downloads/03_certification_criteria_transparent_components_en.pdf

15. Climate Specific Certification:
*PHI now issues
certificates for Arctic,
Cold, Cool-Temperate,
Warm-Temperate and
Warm climate zones.
Note: Criteria for Warm-Temperate and
Warm are provisional and therefore
subject to change.
Images from PHI component Certification
Criteria document:
http://www.passiv.de/downloads/03_certific
ation_criteria_transparent_components_en
.pdf (Updated on 7 Feb., 2015)

16. PHI certification example:
Uw = 0.75 W/m2
K
Uw,installed = 0.85 W/m2
K
Uframe = 0.65 W/m2
K
Frame width
Ψg(spacer) = 0.024 W/mK
fRsi = 0.74
Certified!
Image from PHI component database: http://www.passiv.de/komponentendatenbank/files/pdf/zertifikate/zd_northwin_vision_en.pdf

17. *PHI certification example:
The PHI component seal
Category
Opaque
envelope
Building
services
Transparent
envelope
Efficiency class
phC certifiable component
phB basic component
phA advanced component
phA+ very adv. component
Climate region
Arctic
Cold
Cool,
temperate
Warm,
temperate
Warm
Hot
Very hot
Image courtesy of PHI: www.passivehouse.com

18. And what’s an Efficiency Class?
The Passive House Institute recently added a
scaled rating (phA+ to phD) to their
certificate. It is based on the ratio of
glass to frame and favors thinner frames
which may have a higher u-value than
their wider-framed counterparts.)
ψopaq = ψg + (Uf x Af)/ Lg
Images and info from PHI component Certification Criteria document: http://www.passiv.de/downloads/03_certification_criteria_transparent_components_en.pdf

19. How PHIUS calcs window U-value
For certification:
(Ug*Ag) + (Uf*Af) + (ψspacer*Lg)
Aw
Uw =
Ug
Ag
Uf
Af
Lg
Ug = U-value glass *
Ag = Area glass
Uf = U-value frame
Af = Area frame
Ψspacer = psi
L g = Length spacer
Aw = Area Window
ψspacer
* It appears that PHIUS is using the same simulation protocols as PHI (EN ISO 673, 10077) with
outputs structured in a similar format to the NFRC. It also appears PHIUS is calculating specific
IGU’s for each frame to generate U-window ratings. This info is based on author study of current
PHIUS documentation and has not been confirmed by PHIUS.

20. Uf Boundary Condition:
Temp: 68 degF (20 degC)
Film Coeff: (Rs)
1.35 BTU/hr.ft2
F (7.67 W/m2
K)
PHIUS Therm file protocols:
Ug Boundary Condition:
Temp: 68 degF (20 degC)
Film Coeff: (Rs)
1.35 BTU/hr.ft2
F or 0.74 hr.ft2
F/BTU
(7.67 W/m2
K)
Boundary Condition:
Temp: 14 degF (-10degC)
Film Coeff: (Rs)
4.35 BTU/hr.ft2
F
or 0.23 hr.ft2
F/BTU
(24.69 W/m2
K)
U-factor Surface: Interior
U-factor Surface: Frame
U-factor Surface: none
* Simulation protocols are based on the EU ISO 673, 10077 testing protocols. Author assumption. PHIUS has not confirmed.

21. PHIUS Climate recommendations:
Image from PHIUS info document for window manufacturers – Graham Wright

22. Sample PHIUS certificate:
Simulation:
1. Ufactor (whole window includes
frame + glass)
2. SHGC (specific to each IGU)
3. Visible Transmittance
4. Air Leakage (optional)
5. U cog
6. SHGC cog (not including
frame)
7. Frame widths
8. U-frame values
9. Psi-spacer value
Image from PHIUS info document for window manufacturers – Graham Wright

23. PHPP inputs required for windows:
Ug
Ag
Uf
Af
Lg
Lf
ψinstall
ψspacer
• U- frame
• Frame dimensions
(width of jambs,
header and sill to
edge of glass – Af )
• Ψspacer
• Ψinstallation
• SHGC (or G-value)
• U-glass

24. What are the differences?
So if you just want to build a Passive House…
Chart based on most current info publicly available at this time. This chart does not include specific differences between NFRC
100 and ISO 10077, which vary enough to make comparison difficult. Author will revise as new information becomes available.
Simulation Req'd Yes Yes Yes
Product Test Req'd Yes No No
Simulation Protocol NFRC 100 ISO 10077 ISO 10077
Includes specific IGU Yes 3-options Yes
Minimum U-window Req'd No Yes No
Min. fRsi (Surfac Temp. Factr)No Yes No
Min. U-Installed Req'd No Yes No
*Author’s Evaluation: Fitness Test | Triathlon |Fun Run

25. Good luck!
(Choose your windows and
certifier ahead of time.)
Contact:
Bronwyn Barry
bronwynbarry67 at gmail.com
bronwyn at oneskyhomes.com
Questions?
Thank You!