I could be wrong

Posted Tuesday, March 11, 2014 in Sustainable Maine

I could be wrong

by Paul Kando

In our high school it was a custom to ask teachers  “one last question”  at the end of the last class before graduation.  Here are two answers  that still serve me well:  “The most important thing to remember about science is that we can be wrong. A true scientist is open to revise what he knows in response new, valid information. Everything is open to reexamination”. “Don’t let even the most cherished tradition become a doctrine. History is full of so-called leaders who, by acting as if they were infallible, worked themselves into corners they found impossible to back out of.”  These counsels also apply in the context of  home energy efficiency. After all, fixing our habits can be just as important as plugging cold drafts.  Am I open to change my views and habitual behavior in response to new information? 

“Better let the house breathe” some say, mouthing an unexamined half-truth. Leaky, uninsulated houses, it is true,  have survived centuries without damage, while some recently “tightly built” homes developed mold, mildew and other moisture problems. Does this suggest we should build leaky houses? I think not, but there is a need to learn how to build a tight house the proper way. Heat, air, and moisture interact in a heated building in predictable ways. Moisture evaporates as it warms and warming air absorbs more moisture even as it becomes lighter and rises. In a tight house this moisture-laden air can get trapped. It will enter the structure through cracks and holes, including our inherently leaky electrical outlets. There the air cools and drops its moisture onto a cool surface, such as a wall sheathing or the underside of the roof deck. There the harmless water vapor condenses into liquid water, creating all sorts of problems. A well-designed and built tight house has sufficient heat-recovery ventilation to avoid this problem. Why would anyone build either an expensive-to-heat, energy-wasting, leaky house, or a poorly built tight house with unhealthy indoor air, which gradually self-destructs, when we know how to build it right?

“I want fresh air, so I sleep with the window open”. That’s a great idea all year round, except during the heating season, when the physics of the house change. Now, instead of fresh air streaming in, warm air rising from the floor below is streaming out through your upstairs bedroom window. It is replaced by cool air entering through leaks and drafts in the basement and the lower parts of the house. Therefore, in winter, an open bedroom window invites not fresh air but warmed-up cellar-air into your bedroom. This air has entered cold from the outdoors, absorbed moisture from cellar and house as it was warmed by the heating system. Do you really want this air in your bedroom, only to be exhausted through the open window, along with all that heat energy it absorbed along the way?  Is this the “fresh air” you mean to breathe all night?

“The air is too dry, so we have a humidifier running”. Dry indoor air in winter is a symptom of a leaky house. As the heating system warms the air, it absorbs more and more moisture in the form of water vapor. If this warm moist air is allowed to escape the heated space through leaks (or open bedroom windows), it will take with it the moisture it absorbed, leaving the indoor air dry. To compound the problem, the outdoor air that leaks into the house to replace the leaked out air is, of course, cold. It holds little moisture. Once heated,  it absorbs all the moisture it can find before leaking out. This goes on 24/7. No wonder the indoor air is dry! Adding a humidifier is not the answer. It can easily make things worse, not better: What if the moisture it adds winds up not leaving the house, but lodging inside the structure instead (see above)? The remedy for dry indoor air is a tighter house with controlled, heat recovery  ventilation.

“We open the basement windows in the summer to dry out this musty cellar”. Really? Did you notice the moisture dripping from the cold water pipes? Where did that come from? In summer, it is warmer outside than in the cellar. Warm air holds more moisture than cold. Therefore, through the open cellar windows, warm moist air enters, only to droop its excess moisture as it cools. The moisture condenses on any surface cooler than the dew point – pipes, metal objects like tools, concrete or granite walls are all good candidates. Instead of drying the cellar, you are inviting more moisture in.

Habits are hard to change, especially when reinforced by tradition or sentimental attachment to the way dad, mom, grandma, grandpa did things. But didn’t they just strive to do their best, based on the information they had available?  My dad‘s advice rings in my ear every time I’m tempted to take someone’s word for something I should be investigating: “Don’t let anybody talk you into something you don’t fully understand. Because, like me, they could be wrong!”

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