Oops, it’s leaky!

New York City College of Technology, known as CUNY City Tech, hosts a Fall 2016 Series of Environmental Building Performance workshops on Saturdays. I finally got a chance to join one workshop talking about the blower door test.


Blower door test measures the airtightness of a house or a building. It was first used in 1977 in Sweden. It is used to determine the compliance with code, standard or certification. The New York State Energy Code of 2016 coming into effect on October 3rd requires an airtightness test for all the new commercial buildings as well as all the new residential buildings. If you happen to hate reading regulatory documents like me, I suggest reading the documents on the DOB’s website. It still took me a while to figure out where are the requirements for airtightness. But I have to say it looks much clear and easy to follow with the headlines. You can find the airtightness requirements for residential buildings in Chapter R4, R402.4.1 and the requirements for commercial buildings in Chapter C4, C402.5.1.3. You can also read this article written by Urban Green Council to understand the key changes.

The workshop discussed about the benefits of an airtight house and the failures due to the uncontrolled ventilation and infiltration. Although I have learned a lot about building science, I still learned some new stuffs from the speaker Robert Hothan. Here are two interesting things I learned:

1) The invention of revolving doors

I know stack effect. I see revolving doors everywhere. But I have never thought about the invention of revolving door was actually because of the significant stack effect in skyscrapers. The uneven distribution of heating systems in many skyscrapers further exacerbates the stack effect.

2) The failure of forced-air distribution system

The poorly designed forced-air distribution system (without a proper return air pathway) creates unwanted pressure imbalances within a building. The accumulative pressure in some areas (usually bedrooms) has to go somewhere. OMG, they find their way into the wall and ceiling cavities carrying the moisture. On the other hand, the depressurized rooms with inadequate supply air draws outside air into the building cavities. Boom, condensation happens somewhere within the wall assembly.

When talking about building energy efficiency, we tend to think about delta T (temperature difference). But the speaker, Robert, reminded us delta P (pressure difference) plays an esssential role in building design. I think that’s why more designers and engineers start favoring the controlled balanced ventilation.

Robert spent a little bit time talking about the controlled ventilation solutions: ERV. The versatile ERV can integrate with other energy efficient solutions. For example, ground source heat pump (described as “geothermal” in the U.S. which is misleading) is common in central Europe where people take advantage of the favorable ground temperature and the lower labor cost of excavation. The earth tubes in Europe are not crazy deep. The horizontal tubes cover only a decent area.


After discussing some theories, we were able to see a blower door test demo in a very leaky space. I have seen blower door tests before, but are all in the airtight spaces. On Saturday, the classroom was so leaky that hard to (de)pressurize. But we were excited to feel the draft, here and there, including a small switch.

The smoke tester and thermal imaging camera helped to further show the problematic areas, for example, the ceiling tile connections and wall-to-ceiling connections.


A very controversial question raised up during the Q&A. One participant asked about the necessity of an ERV and the alternative solutions for a well-known brand. The “blind” belief (claiming something be the only best choice) in a particular brand ERV is also my worry. ERV is not the focus of the workshop, neither is this blog. I will write another blog about my personal perspective on ERV.

In summary, this was a very informative and interactive workshop. Robert is a great speaker. He studied in Austria that has a great Passive House to population ratio. The coordinator Professor Kim at City Tech is a knowledgeable expert in building science and has deep insights.


Sometimes I feel my yoga teachers mention things indirectly related to my professional work. Today my teacher talked about the origin of yoga practices. She said many awkward/advanced yoga postures and breathing control techniques were invented to test if the yoga practitioners can stay calm under the challenging conditions. For example, can we hold the breath for several seconds (known as Kumbhaka in Sanskrit)? Will we be anxious or nervous if we hold the breath for 30+ seconds? Can we manually force the exhalation be deep and quick to repel the stale air from the body while allowing the inhalation to be passive (known as Kapalabhati in Sanskrit)? The analogy between yoga breathing techniques and ventilation in a building made my day. Dear architects, engineers, builders, and policy makers, please relax and enjoy this reading about yoga breathing.

Tell you something, I was struggling with morning laziness today. I didn’t realize it’s New Moon until I arrived the yoga studio. New Moon is a time when the energy is lower in comparison to the bright Full Moon. New Moon is a time to self-reflect and set an intention. Full Moon is a good opportunity to discharge: release what no longer serves us, and then inviting an expansion of our minds. Does it sound like a metaphor for a balanced ventilation system we pursue?


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