Editor's Note: Scientific American's George Musser will be chronicling his experiences installing solar panels in 60-Second Solar. Read his introduction here and see all posts here.

Maybe I spoke too soon in my last blog post about having picked all the low-hanging fruit in home energy conservation. Last Friday our local home energy auditor, Tom Testa, came back out to rerun the air-infiltration test he had conducted in November. I was so proud of all the insulating and leak-sealing I’d done over the winter and wanted to show it off.

Instead I found that I’d made some progress, but still have a long way to go.

As before, Testa set up a blower fan in our back door and used it to bring the house to a negative pressure of 50 pascals, which pulled air in through cracks and made them easier to find. To maintain the negative pressure, the fan had to suck out 5,100 cubic feet of air a minute—12 percent less than last time. If less air had to be drawn out of the house, it meant less air was leaking in.

When I saw the number, I felt as deflated as my house. All that work for such a small reduction in air infiltration?

On the positive side, whereas in November there were so many leaks that we didn’t even bother to catalog them one by one, this time the problem seemed more manageable. We went around the house with a smoke stick to pinpoint the remaining leaks and made a list of about two dozen of them. My wife’s study had a particularly elusive one. We could feel it and hear it—it was giving off a high-pitched whistle. But it took 10 minutes of searching to find it: behind a piece of vinyl in the window frame was an open screw hole that was acting like a pitch pipe.

The test exaggerates the natural air circulation of the house and, in so doing, created some seepage that probably doesn’t occur under ordinary circumstances. For instance, the high air flow rate yanked the attic door away from its weatherstripping. When I held the door shut with my hand, the flow rate dropped by 100 cubic feet per minute.

In any case, I now have my marching orders. My experience shows that a home energy audit isn’t just a one-off event—it’s something you need to do several times to guide your efforts.

Blower door set up by energy auditor Tom Testa, courtesy of George Musser