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.

Last fall, before we decided to go solar, my wife and I had done a fair amount of work on weatherstripping and insulating and had reached a decision point on what to do next. Get a new back door? Replace the decrepit dining-room windows? Fix the bull-headed T in our steam heat piping? (Plumbers’ jargon is even more colorful than astrophysicists’.) In an old house (ours dates to 1868), there are always more projects than time or money, and I hoped an outside expert would help us choose. Besides, I thought an infrared scan of our walls, showing the heat flow in vivid false color, would be cool.

My wife was put off by the $450 price tag charged by local energy auditor, Tom Testa of Home Energy Diagnostics, but knew that she couldn’t stand between me and thermal imaging. (As it turns out, if you want New Jersey state subsidies for installing solar power, you need a home energy audit, so we would have ended up bearing the cost anyway.) I hired Testa in September, and he spent nearly half a day at our place in early November, when the temperature difference between inside and outside was large enough to ensure good infrared readings.

The imager looked like a cross between a digital camera and a cordless drill, and it was definitely fun to play with. If you touch the wall with your palm, the imager will show the thermal handprint. Testa used it to check the quality of wall and ceiling insulation. A house of the age of ours doesn’t have fiberglass insulation or housewrap. Instead, wedged between the interior plaster wall and exterior clapboard is a non-load-bearing wall of bricks. Their insulation value isn’t great, but Testa said it’s good enough that trying to retrofit something better wouldn’t be worth the hefty cost.

For the attic and those walls that lacked brick fill, we’d brought in a contractor several years ago to blow in cellulose insulation, which is basically confetti. Evidently they screwed up. The imager revealed cold spots around the top of the walls where the cellulose had settled. It also found a spot on our kitchen wall that was the outside temperature—the dark spot in the photo above. Later, I took a closer look and found that the exterior siding in this area had bent back and exposed the wood to the elements. We ended up having to shell out $1,000 to replace part of a load-bearing beam.

On the whole, though, Testa said we’d get the most bang for our buck by focusing not on insulation but on air leaks, which carry away a huge amount of heat. To ferret them out, Testa used a lower-tech device: the blower door. He propped open the back door to the house and covered the gap with a canvas door with a circular opening. He inserted a fan and started sucking air out of the house. A controller regulated the fan to bring the house to a negative pressure of 50 pascals, or roughly 0.01 pound per square inch. That, in turn, pulled in air through every crack and crevice, making it easy to pinpoint air leaks.

In fact, the fan turned our house into a scene from Poltergeist. Doors slammed shut. Windows hissed. Gale-force winds poured out of our attic door. To maintain the negative pressure, the fan had to pull 5,800 cubic feet of air a minute through our house, nearly three times as much as in a properly sealed house. Our walls were sieves.

To get a grip on the problem, Testa advised concentrating on choking off the house’s chimney effect. Outside air enters the basement, rises, and vents out the attic. This overall circulation pattern is more important than local problems such as single-glazed windows. Testa said there will be a human colony on Mars before new windows paid themselves off.

So we added weatherstripping and rigid foam insulation to the attic door. In the basement, we got a contractor to close off the leaky bilco cellar door with a proper fiberglass exterior door and seal the rim joist (the part of the basement wall between the ground level and the first floor) with foam boards. Two thousand dollars later, I get the feeling that I’m running my own stimulus package for the local construction industry.

Now, every weekend, I go on hole patrol. I kiss my wife and daughter goodbye and disappear into the basement with cans of spray foam, tubes of caulk, and sheets of foam insulation. I feel for drafts and look for telltale signs of air flow such as cobwebs. I’m just astounded by how many holes our basement had once I began to look for them in a serious way. It’s a miracle of Victorian overengineering that our house hadn’t just collapsed. If President Obama thinks we can rescue our economy by putting people to work sealing up houses, the amount of time I’ve put into our basement suggests he’s right.

Although we haven’t had enough gas meter readings since we started the work to tell whether we’ve recouped our investment, we’ve noticed a definite improvement in comfort. The temperature differential between upstairs and downstairs is much less than it was, and we don’t need to wear sweaters in our kitchen on winter days anymore. I’m not sure the audit told me anything I couldn’t have figured out on my own, but like others, I found it a real eye-opener.

Thermal infrared image of George’s kitchen wall, courtesy of Tom Testa