Air-sealing vs. Trump

Donald Trump speaking at a rally in Arizona, 2018courtesy Gage Skidmore.


How can I get you interested in air-sealing buildings instead of Donald Trump?


It’s a hard one, I know.

Air sealing of buildings is just not that interesting. There is no shiny tech to promote. It is not the result of smart new research. Not to mention it is a bit hard to explain and harder to perceive. It’s mostly hidden, generally unheard of, dispersed everywhere, and it does not have an industry trade group to promote it. And if I was to ask, I suspect that you would not feel there is anything wrong with your building.

By contrast, the Commander-in-Chief is a genius of interesting-ness. He has made himself into that itch you cannot get enough of scratching. The uncle you can’t wait to get into it with; the target begging to be destroyed. I can’t wait to see him get what’s coming to him. Or, from the other perspective: I can’t wait to hear him tell all those fools off again. I’m right there with you, tuning in every morning. He has perfected the art of attracting all our attention and energy onto himself, and we are game.

But he is not stopping us from doing something else.

Air leaks into and out of our buildings. Hot air rises. Inside a building it rises up and makes pressure at the top. Enough pressure to push air out. Which then makes suction at the bottom, drawing cold air in. Or, the wind blows. Again, a pressure differential is created moving air between inside and outside. Air that leaks out is the nice comfortable temperature that we want it to be, saying goodbye. Unless you live in Southern California, the air that’s sucked in probably is not. So we have to change its temperature, using (of course) heating and air conditioning, which (of course) take energy. The most energy.

The amount of energy we use on heating and cooling dwarfs every other building energy else. In our homes, per the U.S.DOE, heat and A/C consume a full 54% of all energy in buildings. Hot water is a distant second at 18%. Light bulbs? Only 6%. Again, perhaps not true if you live in So Cal. But likely more true if you live in Vermont or Idaho. It’s certainly true here in NYC. That’s something like 12% of all the energy used in the entire USA. Twelve percent. Commercial buildings are a little different, but not that much. Taken together across all building types, heating and cooling consume close to 20% of all US energy consumption. 20% of all the energy used in the USA goes to heating and cooling buildings. Renewables cover only a tiny, slow-growing slice whose rate of expansion barely keeps pace with the expanding rate of demand.


Building energy uses and sourcesU.S. Department of Energy


Most folks get the gist of insulation. It’s like a nice fluffy blanket. Very few get air sealing. Insulation is good. But are you going to rip off your still-newish siding just to put some on? Or re-Sheetrock the inside of your home? And what good does that blanket do you if there is a cool breeze blowing through it? Air infiltration accounts for every bit as much heat loss as the conductive transfer addressed by insulation, and it is a heck of a lot easier to fix. Air sealing is more important than equipment and usually cheaper. And what sense does it make to invest in a new, expensive, only-incrementally-better version of that same old heater if you’re installing it into the same drafty old guzzler of a building? In most existing buildings, unless you are still using incandescent light bulbs, air sealing is the lowest of low-hanging fruit. If you are building new, air sealing is free.

If you are like most folks, it will surprise you to learn where that air leaks into and out of. Through the ground. Through solid brick walls. Between pieces of wood screwed tight together. How do I know? I have tested buildings and seen it happen. And it is common knowledge. In my own apartment I have a closet light switch with a broken cover plate. When the wind blows outside, it also blows right out that switch. Where the heck does that come from? Through the Swiss cheese that is my apartment building. It comes around penetrations for pipes, wires, vents, joists, beams, and partitions, around framing, windows and doors. Not to mention that giant open chimney flue.

There is a standardized test of building air infiltration. It calculates ACH50, or air changes per hour at 50 Pascals. This is the number of times in one hour that all the air inside a building is completely sucked out and replaced with air drawn in through walls, roofs, etc, when there is a continuous pressure difference of 50Pa between inside and outside. 50 Pascals is akin to what you get from a strong wind blowing nonstop on the side of a building. This test is the blower-door test, and the unit is ACH50 – the air-leaky-ness of buildings apples-to-apples independent of building size. Any decent home energy audit includes this test. My father’s 20-yr old Oregon ranch house tested at 12 ACH50. Years ago I helped a colleague with a down-to-the-studs gut renovation of a house in Connecticut which achieved a good Energy Star rating. When finished it tested at about 4 ACH50. One of the four performance metrics required to meet the ultra-efficient Passive House Certification Standard is to pass a test at or below 0.6 ACH50. Here in NYC? I’ve helped a lot of well-intentioned folks get city approvals to put solar arrays on top of their beautiful historic townhouses. Those houses often test above 20 ACH50. Given what thousands of Passive Houses have shown to be readily possible, our buildings range from mediocre to absurd.



Are you still reading? I hope so. I’ll refrain from Trumpian tactics. But in return, you will continue?

How much of that 20% of all US energy consumption can be saved just by reducing air infiltration? As suggested by the above, it varies a lot. Here are some estimates and anecdotes:

  • Lawrence Berkeley National Laboratory estimated savings from a range of home air-sealing reductions. Their model projected that savings from air sealing American homes to 3-5 ACH50 would reduce total US residential energy use by 20%. That is after introducing necessary fresh-air ventilation. No new insulation, no high-tech equipment, only air sealing.
  • Efficiency Maine did an air-sealing program for 8,000 homes a few years back. The evaluation report of the completed program calculated that, for an average cost of $850, in a mere 6-10 hours, contractors reduced air flow by 17% and whole-house energy usage by 13.5%. 13.5% in one day’s work! They sealed dumb stuff like attic hatches, loose windows, and plumbing chases.
  • NYC is probably worse. Urban Green, the local chapter of the US Green Building Council, commissioned two studies to highlight impacts specifically attributable to just two ubiquitous local practices. They estimate that a full 1% of all the CO2 emissions from the entire City of New York come from fuel needed to heat air lost through gaps around personal air conditioners installed in windows and through-wall sleeves. One full percent because of sloppy gaps around folks’ A/C’s. I believe it. Looking out right now (in January) I count five window A/C’s in view. They also singled out the wide-open holes that NYC requires at the top of elevator shafts to be responsible for 80,000 barrels of oil annually, just in buildings over 10 stories tall.
  • The National Institute of Standards and Technology has for a while been debunking the idea that commercial buildings are tighter. They conducted a study to back up recommendations that building codes should require specific air-infiltration rate requirements. They projected up to 40% savings in commercial buildings by air sealing alone.
  • Anecdotally, I have one colleague who says he reduced his parents’ gas bill 40% by crawling around and air sealing only the attic. Another, who does energy modeling for a living, typically finds that a leaky house can have 25-35% of the total heat demand attributed to infiltration. In my own work I have seen a single tiny space heater keep an entire well-sealed building warm during a single-digit cold snap, which is really cold for around here.

Air sealing truly comes down only to education and culture, not cost or technology.

So why is it ignored? Simply because there has been no broad social imperative to reduce building energy use, and therefore no strong drive to change energy-related construction culture. Looking back, I think we can all recognize this is true. This aspect of building performance was identified in the 1970’s and some folks have been paying attention ever since. But energy has been cheap and the consequences of its use remote, so as a group we Americans have ignored it. There has been, and remains, no social accountability for energy use, so the people that make buildings have understandably prioritized the things they are held accountable for: comfort, looks, life-safety, and profit. Comfort achieved through energy use. Including almost all of my dear colleagues. Architects and builders. Engineers and home inspectors. Developers and realtors and homeowners. Solar installers and the makers of those overly-complicated ground-source heat pumps. And the government? The custodians of the building codes are only recently coming around. After all, they are held to the same norms as the rest of us.

I would offer that it is a mistake to look to our institutions or national government to lead the way. In our great American system, that is the role of We the People. I would argue for personal education, individual action, clear thinking, and prioritization of inevitably limited resources of time, money, and attention. Starting, if you are responsible for a building and you are concerned about Climate Change, with boring air infiltration. Donald Trump is a distraction.

Donald Trump is not stopping us from fixing our buildings.