Housewatch: Energy Audit Hits Close to Home

After years of telling readers that Americans can help reduce global warming by using less energy at home, it was time for me to put my money where my mouth was and learn how my own house could become more energy efficient.

Last month, I asked Nate Munson, a home-performance energy specialist based in Manchester, Mich., and his assistant, Brian Brickley, to come to my house for an energy audit. For 2 1/2 hours, they conducted tests, poking into every nook and cranny and taking countless measurements, all to figure out how much energy we use for heating and cooling. I focused on heating and cooling because together they are the biggest consumers of home energy and, as most houses are not heated or cooled efficiently, they offer the greatest potential for savings.

A week later, we got the results. With a 50-year-old house, we are doing well but could do better. Two critical numbers summarized our test results.

The first was the Home Energy Rating System (HERS) index, which rates overall energy efficiency. A new house built to the 2006 International Building Code standard must have a rating of 100 or less. The lower the HERS index number, the more efficient the house. A new house with the Energy Star designation has a HERS index of 85 or less.

Our HERS index was 106, but older houses in our area typically register about 130, Munson said. The secret of our energy-efficiency success was that we had made a number of improvements over the past 10 years, including adding insulation and replacing all the windows.

The second important number was the air changes per hour (ACH), which tells how many times an hour the entire volume of heated or cooled air in the house is replaced with outdoor air. The higher the ACH, the more energy you'll need to heat and cool your house.

The ACH for our house was 0.38 during the summer (every hour about a third of the cooled air in our house is replaced with outside air) and 0.50 for the winter (every hour about half of the heated air is replaced). Most houses as old as ours have an ACH of about 1.2, meaning they are more than twice as leaky, Munson said. The ACH figure is higher during the cold season because the difference between the indoor and outdoor temperature is much greater, Munson added.

Munson's testing was straightforward and instructive. The first phase focused on air leaks. The team placed a large fan in the opening of our front door to create negative pressure (air leaking in instead of leaking out). Then, Munson used a "puffer wand" in each room to expel a small plume of smoke to check openings in exterior and interior walls for leaks.

I expected this test to turn up some air leaks, but the results were surprising. Leaks showed up in every register for heating and air conditioning, every outlet and light switch, every recessed light fixture on both floors, and almost every replacement window. This last discovery was especially annoying because the replacement windows were supposed to eliminate this problem.

The second phase of the energy audit focused on winter heat loss and summer heat gain through our exterior walls. Munson also looked for the presence -- or absence -- of insulation. For this part of the audit, he used a video camera that could display infrared pictures of each room.

Munson recommended several improvements. I sifted through his report and tried to figure out which projects made the most sense for us. If we did everything on his list, our HERS index would go down to an Energy Star level of 82. Our heating and cooling energy consumption would fall by about 30 percent, and our total energy consumption by about 12 percent.

The most obvious of Munson's suggested improvements was the most costly -- $1,500 for plugging up all of our air leaks. This would reduce the winter ACH to 0.38 and the summer ACH to 0.28, cutting our heating and cooling energy use by about 12 percent.

When the ACH dips down to 0.35 or below, however, most building codes -- including ours -- require mechanical ventilation to ensure that the occupants have enough fresh air. We would have to install a continuously operating, variable-speed bathroom ventilating fan, which would cost about $150, Munson said.

Munson's infrared tests showed that we have no insulation on the outside perimeter of our house between the floors. This finding was disheartening because we assumed that this had been addressed when we beefed up our insulation five years ago.

Since our basement is only partially finished, perimeter insulation between it and the first floor above can be easily added. But the framing between the first and second floors is inaccessible; perimeter insulation there requires a "surgical approach" going through from the floor above or from the ceiling below and using a more costly closed-cell spray foam. This $500 improvement would reduce our heating and cooling energy by about 6 percent.

Munson also recommended insulating the basement foundation walls. This $300 improvement would increase the comfort level on the first floor during our cold Michigan winters and reduce our heating energy use by about 8 percent.

After factoring in tax credits and utility rebates, I realized that all of the recommended improvements made sense. If we can get everything Munson suggested completed before Dec. 31, we can claim a $1,500 credit on our 2009 federal income tax return for energy-efficient home improvements, and a $545 rebate offered by our local utility. That would bring the total out-of pocket expense to $405. With an expected annual savings of $290 in utility bills, we would make up that cost in less than two years.

Katherine Salant can be contacted via her Web site, http://www.katherinesalant.com.

© 2009 Katherine Salant