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Musings of an Energy Nerd

Martin’s Energy Quiz — Third Edition

Sharpen your pencils — it's time once again for the energy quiz

Remember, Googling isn't allowed.

GBA published an energy quiz in 2009, and another one in 2011. It looks like we’re overdue for another installment.

Answers are provided at the bottom of this column; don’t peek until you’ve finished the quiz.

1. True or false: In freezing climates, a drainback solar hot water system circulates ordinary water (without any antifreeze) through its solar collectors.

(a) True.

(b) False.

2. Which of the following statements best describes the “cold OSB problem”?

(a) OSB sheathing is more at risk when stud cavities are filled with thick insulation than thin insulation.

(b) When OSB gets very cold, the adhesive that binds the wood flakes may fail.

(c) OSB can fail if it is covered on the exterior with a thick layer of rigid foam.

(d) Researchers have not succeeded in developing an OSB sleeping bag.

3. The International Residential Code includes a table listing prescriptive requirements for insulation and windows. The column labeled “fenestration U-factor” shows:

(a) Minimum U-factors for windows.

(b) Maximum U-factors for windows.

(c) The confusion rate for readers with low Understanding Factors (i.e., low U-factors) who are forced to decipher code documents.

4. Which of these statements is true?

(a) No roof assembly can dry to the exterior.

(b) All roof assemblies can dry to the exterior.

(c) Some roof assemblies can dry to the exterior.

(d) Roofs in Seattle are always wet.

5. Which of these statements is most likely to be true for a certified Passivhaus?

(a) The house has Zehnder windows, a Siga heat-recovery ventilator, and Intus tape.

(b) The house has Intus windows, a Zehnder heat-recovery ventilator, and Siga tape.

(c) The house has Siga windows, an Intus heat-recovery ventilator, and Zehnder tape.

(d) The windows cost too much.

6. Compared to exhaust-only ventilation systems, heat-recovery ventilation (HRV) systems have several advantages. Which of the following statements is false?

(a) HRV systems do a better job of distributing fresh air than exhaust-only systems.

(b) Unlike exhaust-only systems, HRV systems draw air from a known location.

(c) HRV systems use less electricity than exhaust-only systems.

(d) Although HRV systems cost more to install than exhaust-only systems, an HRV installed in a cold climate can save money in the long run compared to an exhaust-only system.

7. Which of the following statements is true?

(a) It’s easier to keep south-facing windows from causing overheating problems than west-facing windows.

(b) In a cold climate, you can’t have too much south-facing glazing.

(c) If you are choosing a sloped building site in a cold climate, a north-facing slope is preferable to a south-facing slope.

(d) An earthship is a sailboat made of old tires and rammed earth.

8. To reduce the cooling load of a hot-climate house, which of the following measures is least likely to help?

(a) Specifying windows with a low solar heat gain coefficient (SHGC).

(b) Moving ductwork from the unconditioned attic to a location inside the home’s thermal envelope.

(c) Specifying wall insulation with a higher R-value than the minimum code requirement.

9. In climate zone 3, a proposed cathedral ceiling contains 6 inches of closed-cell spray foam on the underside of the OSB roof sheathing. Above the sheathing is a layer of Titanium UDL synthetic roofing underlayment and asphalt shingle roofing. This roof assembly doesn’t meet code. To make the assembly code-compliant:

(a) The roof assembly needs a higher R-value.

(b) There needs to be a ventilation channel between the top of the insulation and the underside of the roof sheathing.

(c) The builder has to choose a different roofing underlayment.

10. Which of the following statements is true?

(a) Heating a house with ductless minisplit units usually costs more than heating a house with fuel oil.

(b) In most climates, a single minisplit unit can heat a small single-family house with an open floor plan, but the bedrooms are likely to be colder than the living room in winter if the bedroom doors are closed.

(c) Air-source heat pumps can’t be depended on for heat when the outdoor temperature drops below 20°F.

(d) Everyone agrees that a ductless minisplit head is a stylish way to spruce up the appearance of your living room wall.

11. Which of these answers best describes the conditions under which condensation develops on the exterior side of triple-glazed windows?

(a) When the indoor humidity is high.

(b) When the outdoor humidity is high.

(c) When the sky is very clear and the morning air is cool.

(d) When your neighbor comes over to admire your expensive new triple-glazed windows.

12. Which of the following appliances does not have a condensate drain?

(a) A natural gas clothes dryer.

(b) A heat-pump water heater.

(c) The outdoor unit of a ductless minisplit system.

(d) A condensing furnace.

13. Stains on asphalt roofing are most often caused by:

(a) Algae.

(b) Mold.

(c) Mildew.

(d) Santa’s reindeer.

14. A copy-editor is reviewing an article on a certified Passivhaus. The original document is smudged and hard to read. Which of these numbers is the most likely value of the blower-door test?

(a) 58 ach50

(b) 5.8 ach50

(c) .58 ach50

15. Joe Lstiburek walks into a new house in Houston, Texas. The homeowner proudly announces that the ventilation system is providing fresh air at the rate recommended by the 2013 version of ASHRAE 62.2. Which of the following statements is Joe most likely to make?

(a) “That’s the best ventilation standard in America. It sounds like your builder knew what he was doing.”

(b) “For crying out loud, reduce the ventilation rate!”

(c) “Fresh air is healthy. You need to ventilate at a higher rate.”

16. The main difficulty encountered by builders who install mineral wool insulation on the exterior side of wall sheathing is:

(a) It can be hard to get the furring strips co-planar.

(b) Mineral wool insulation restricts a wall’s ability to dry to the exterior.

(c) Mineral wool insulation must be protected from rain during construction.

17. If you want to install exterior rigid foam on your walls in a cold climate, thin foam is riskier than thick foam. Which of these statements provides the best explanation of this problem?

(a) Thin foam is not as good at resisting inward solar vapor drive.

(b) Thin foam is unable to keep the OSB or plywood wall sheathing above the dew point in cold weather.

(c) Thin foam is more likely to compress, leading to wavy siding installations.

(d) Walls have to breathe.

18. Time for a cool roofing question: Which one of the following statements is true?

(a) Emissivity is the same as emittance.

(b) Solar reflectance is the same as thermal emittance.

(c) Permeance is the same as permeability.

(d) Most HVAC contractors know how to perform accurate load calculations.

19. Which of the following statements best describes the phenomenon of condensation?

(a) When warm, humid air comes in contact with a cold, hard surface, droplets of water form on the surface.

(b) When cold, dry air comes in contact with a warm, hard surface, droplets of water form on the surface.

(c) When cold, humid air comes in contact with a warm, hard surface, droplets of water form on the surface.

(d) I’m supposed to remember to use a coaster, or else my beer can will leave a ring on the coffee table.

20. Wolfgang Feist, Katrin Klingengerg, Mike Eliason, and Bronwyn Barry walked into a bar in Laramie, Wyoming. The bouncer (who was a part-time Passive House consultant) flinched when he saw the gang of four approach, and insisted that they all surrender their handguns at the door. Surprisingly, the four customers shared a table, and after they finished their first round of drinks, it became clear that they were all getting along famously. The bartender, who was eavesdropping, realized that they were telling Joe Lstiburek jokes. He heard Dr. Feist ask, “What do you call a famous building scientist who gets thrown out of a bar?”

(a) Dr. Lstiburek.

(b) Joe.

(c) A bounced Czech.

Answers. 1: a. 2: a. 3: b. 4: c. 5: b (and perhaps d). 6: c. 7: a. 8: c. 9: b or c. 10: b. 11: c. 12: a. 13: a. 14: c. 15: b. 16: a. 17: b. 18: a. 19: a. 20. c.

Martin Holladay’s previous blog: “All About Radon.”

Click here to follow Martin Holladay on Twitter.


  1. User avater
    Dana Dorsett | | #1

    Is there a (politically) correct anwer for #20?
    Given that JoeL hails from the wilds of Canuckistan ( thus not a REAL American ), and not from the Czech Republic how are we supposed to parse the questions/answers? ;-)

  2. User avater GBA Editor
    Martin Holladay | | #2

    Response to Dana Dorsett
    Good catch! Everyone gets to add one point to their score because of my error.

    I have corrected the phrasing of question #20. Even if it is isn't technically correct, I'm still not changing the punchline.

  3. Dan Kolbert | | #3

    What do you call the German who gets stuck with the tab?
    Sour kraut.

  4. Dick Russell | | #4

    Awwww! I got #18 wrong. I
    Awwww! I got #18 wrong. I picked "c", not "a". Educate me, Martin. Actually, I enjoyed more the obviously impossible answers more than the rest of the test. Most entertaining were 3c, 7d, 11d, and 13d.

  5. User avater GBA Editor
    Martin Holladay | | #5

    Response to Dick Russell
    Emissivity and emittance are synonyms.

    Water vapor permeability is the rate of water vapor diffusion through a sheet of any thickness of a material. Permeability is a property of a material. For example, the permeability of polystyrene insulation is a certain value, independent of whether the polystyrene piece in question is 1 inch thick or 3 inches thick. Permeability is measured in grams per Pascal per second per meter (metric units) or perm inches (English units).

    On the other hand, permeance is the measure of the ease with which water vapor passes through a unit thickness of a material; it is not a property of a material. For example, the permeance of 1 inch of XPS differs from the permeance of 2 inches of XPS. Permeance is measured in grams per Pascal per second per meter squared (metric units) or perms (English units). One perm is equal to 1 grain of water vapor per hour per square foot per inch of mercury vapor pressure difference.

  6. Donald Endsley | | #6

    I disagree with #18
    While Emissivity and Emittance are sort of synonymous, they are not the same thing. Emissivity is a material property, Emittivity refers to a specific example. ie: Emissivity is theory, Emittivity is reality. But that's just me being a pedantic jerk. It's probably because I've been doing tests like this for the past few nights at work for my employer required CE.

  7. User avater GBA Editor
    Martin Holladay | | #7

    Response to Donald Endsley
    I'm always willing to learn and admit error when I'm wrong. Can you point me to a reference work that supports the distinction you are making?

  8. Donald Endsley | | #8

    Like I said I was

    Like I said I was just being pedantic. It mainly stems from the suffix of the words. the Suffix -ty refers to a materials ability to do something, -ance is what it is actually doing. They are so close in meaning that for most people it really doesn't matter. I would just say use Emissivity when talking about a material property, and Emittance when talking about the measurement. ie: this window was measured with a Thermal Emittance of 0.8 vs. the manufacturer states the emissivity of this window is 0.8. (I'm not sure why I switched to emitivity from emittance before).

  9. Dick Russell | | #9

    Always check the units
    However the terms may be confused, it always makes sense to check the units of a number, in case the wrong term has been used. Besides telling you whether the value is for an English or metric set of units, you see right away if the value is for a unit of thickness or for the total thickness of the material in question.

  10. Kim Shanahan | | #10

    Are we grading on a curve?
    I'll cop to missing five, which I think makes me a solid C-student. I do seem to get better every year, however. 16 &18 I got wrong and definitely guessed, but I was pretty sure I had three others correct with 2(d), 11(b), and 13(c). In #2, I don't know why thicker insulation would put OSB at risk (and am certain there are no OSB sleeping bags yet developed). In #11, I've never seen condensation on the exterior of a triple pane window in the clear, cool, dry air here in Santa Fe (what is humidity anyway?). And for #13, algae? Really? Is that like moss? Can I again claim regional ignorance?

    Martin, Thanks for the fun challenge. You never fail to make me feel like an idiot.

  11. User avater GBA Editor
    Martin Holladay | | #11

    Response to Kim Shanahan
    Thicker insulation between the studs puts OSB at risk because it makes the OSB colder (and therefore wetter) during the winter. For more information on this issue, see How Risky Is Cold OSB Wall Sheathing?

    The best of the available answers for #11 is (c). That doesn't mean, of course, the you'll get condensation on the outside of your triple-glazed windows every time you have a cool morning and clear weather. The condensation occurs under the same weather conditions that produce dew on grass -- a phenomenon that requires a certain amount of moisture in the air. (I'm guessing from your comment that you don't have much dew in Santa Fe -- or, for that matter, much grass.)

    This type of window condensation also requires that the window be pointing at the sky, because it is a result of night-sky radiation. The window pane is losing heat to outer space. For that to happen, there must be no trees in front of it. The phenomenon is more common on homes located on a hillside, on windows that look downhill (and therefore "see" more sky).

    Kim, I hope that the fun factor exceeded the "feel like an idiot" factor.

  12. Clayton DEKORNE | | #12

    Can you explain #9 ?
    The IRC (both 2009 and 2012) states:

    5.2. Air-permeable insulation only. In addition to the air-permeable installed directly below the structural sheathing, rigid board or sheet insulation shall be installed directly above the structural roof sheathing as specified in Table R806.4 for condensation control.


    I understand 5.2 ... why a permeable insulation needs rigid foam over the roof sheathing for condensation control. I don't understand the way the Table heading is worded ... or why you are suggesting (I think) rigid insulation might be required over closed-cell foam in your proposed assembly. What am I missing? Doesn't R-39 meet the insulation requirement for CZ3 ... even under the 2012 IECC?

  13. User avater GBA Editor
    Martin Holladay | | #13

    Response to Clayton Dekorne
    I'm not suggesting that there is any need for rigid foam above the roof sheathing with this assembly.

    Instead, I'm suggesting that it is a violation of the manufacturer's installation instructions -- and therefore the code, since the code requires all building materials to be installed in accordance with manufacturers' instructions -- to install a vapor-impermeable synthetic roofing underlayment over an unvented roof assembly.

    Here is a quote from the installation instructions for Titanium UDL: "It must be installed above properly ventilated spaces (follow ALL building codes applicable to your geographical regions and structure type) as it is considered a vapor barrier (.06 perms)."

    As with most of my questions, it was a trick question. The point was to educate users of synthetic roofing underlayment that most of these products are not suitable for use over unvented assemblies. You need to stick with ordinary asphalt felt for this type of assembly.

  14. Clayton DEKORNE | | #14

    cool ...
    that helps. thanks ... though, fwiw, I still don't under stand the IRC Table heading.

  15. User avater GBA Editor
    Martin Holladay | | #15

    Response to Clayton Dekorne
    If you want, you can install vapor impermeable insulation directly above the roof sheathing or directly underneath the roof sheathing. This creates an unvented roof assembly. You need to meet certain minimum R-values if you go this route -- or else the impermeable insulation won't be thick enough to keep the interior face of the vapor-impermeable insulation (or the interior side of the roof sheathing, in the case of insulation installed above the roof sheathing) above the dew point in winter.

    I agree that the title of the table is a little confusing. A better title would be, "Minimum R-values for air-impermeable insulation installed above air-permeable insulation."

    But code writers aren't editors, are they?

  16. Derek Roff | | #16

    Still pondering question 9
    Aren't answers b (ventilation channel) and c (different underlayment) both valid solutions for correcting the code-compliance problems of the described roof assembly? If not, please explain what makes a ventilated roof assembly unacceptable.

    I enjoyed the quiz, and learned a few things from it. I enjoyed the joke answers, too, but 'd' is the most correct answer to question 5 on a percentage basis, especially if you include more locations than just the USA.

  17. User avater GBA Editor
    Martin Holladay | | #17

    Response to Derek Roff
    While I was trying to structure Question #9 to be a question about roofing underlayment, you are exactly right -- b is an acceptable answer. I have correctly the answer key to reflect your observation. Of course, the fact that there are two correct answers just underlines the fact that it was a poorly structured question. Thanks for pointing out the flaw.

    Concerning answer (d) for Question #5 -- the answer key always allowed it as a possible correct answer. In that case my joke got away from me, and I left it in even though it muddied the answer selection process.

    Thanks to all GBA readers who gave my quiz more scrutiny than I did.

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