As part of President Obama's stimulus package, nearly $5 billion has been distributed nationwide since March 12 to promote home weatherization, the process of reducing energy bills by upgrading the insulating capability of houses. Michigan has received about $243 million to benefit low-income families by improving the energy efficiency of their homes, a huge increase from the $15 million Michigan usually receives each year to weatherize homes. The plan vows not only to make Michigan more energy friendly, but also to lower energy costs for low-income families, create jobs and improve the resale value of houses. In general, homes with occupant incomes below 200 percent of the federal poverty level or 60 percent of state median income (whichever is greater) are eligible to receive weatherization subsidies. Both homeowners and renters are eligible for weatherization services, and a total of 33,000 homes are expected to be weatherized, with a maximum of $6,500 spent per house. 

Weatherization can be accomplished by insulating ceilings and walls; replacing water heaters and furnaces; or replacing windows and sealing air leaks. 

Home weatherization research took off in the 1980s at the Princeton Center for Energy and Environmental Studies. During a project looking at low-income housing, researchers measuring the heat transfer from living spaces into the attic found that heat losses were three to five times larger than what was predicted by the routine calculations. The reason was that the materials used in walls and ceilings were full of holes and cracks, which allowed air to move through the insulation. Insulation is measured by its resistance (R), which can be degraded by as much as 70 percent, so that R19 insulation may end up only providing an R6 effect, depending on the house in which it is installed. Since R value in itself was not a sufficient measure, the researchers at Princeton developed what is knownas the "blower door," a diagnostic tool that is used to blow air into a building and measure its airtightness and locate leaks, determining where insulation should be put. In the original article on the research featured in National Geographic, Kenneth Gadsby and Gautam Dutt estimated that by fitting all of the nation's residences with adequate insulation, the U.S. could save the equivalent of two-thirds of its foreign oil imports.

 One of the people who worked with the Princeton team was Don Nelson, now president of D.R. Nelson andAssociates. His company pioneered the application of so-called building science innovations in America in theearly 1980s, and has delivered solutions to more than 100,000 homes since.

"The rate of air leakage," Nelson told MichiganScience, "affects how everything else in the house performs, such as insulation. In building science, we take a look at how the house performs as a system and how all the elements go together, and air leakage is the key element."

Nelson, however, calls the nation's focus on weatherization a "cookie-cutter approach," with its primary focus on windows and insulation of ceilings, even though those are the least cost-effective changes in a state like Michigan, where winters are harsh and summers are mild.

"It's as if they didn't learn anything from the '80s," he said. "After President Carter, there was a fair amount of federal money aimed at low-income people to try and do weatherization programs. The problem was that money was simply put at windows or ceiling insulation."

Nelson points to Washtenaw County, which is set to receive $4.2 million to be used for weatheriation over the next three years and talks about blower doors in a 2009 proposal, but does not outline aims for performance testing or goals for how airtight structures must be.

In Michigan, the administration of the weatherization money is being carried out by the Michigan Community Action Agency Association. Jim Crisp, executive director, says the 30 member organizations of MCAAA can sometimes spend as much as $25,000 weatherizing a house, including money from the Department of Energy and the Michigan State Housing Development Authority.

"We can do sidewall insulation or attic insulation, or we insulate basements," Crisp told MichiganScience. "The savings-investment ratio has been re-evaluated from 2:1 to 1:1, meaning that for each dollar spent, there has to be $1 in energy savings. We find that our usual investment in the project is usually around $2 back for every dollar spent."

But as Nelson explained, fixing windows and ceilings are the least effective ways of spending money on weatherization. Using software developed under contract from the U.S. Department of Energy and the Environmental Protection Agency, he has analyzed how energy efficient a house can be with different forms of weatherization. Take for example a typical 1,000-square-foot ranch built in the 1950s with low-grade insulation. Nelson can predict how much money and energy it would take to heat and cool the house.

Furthermore, there's a direct correlation between energy consumption and carbon exhaust that can be measured as well. Nelson's calculations are shown in the chart.

"Perhaps it's not wise to spend $6,500 on every house," he said.

Iain Walker, a researcher at Lawrence Berkeley National Laboratory and a specialist in thermal distribution systems and ventilation, says windows are the last thing that should be done to improve a home's energy efficiency.

"Windows should only be replaced for energy conserving reasons if you have already done everything else," Walker explains, "although there are other excellent reasons for window replacements which override energy conservation efforts, such as condensation resistance or if the old windows are rotted out."

He emphasizes how important it is to have aims for performance testing and goals for how airtight a structure should be, for example when performing blower door tests.

"We don't know much about houses, but we do know that if you don't measure things like airtightness, you have no idea how much you improved a home," Walker said.

According to Stacie Gibson of the Michigan Department of Human Services, which administers the weatherization funds, a pre-inspection done by contractors on the local level determines which methods meet the savings-investment ratio and are most cost-effective.

"It can be attic, floor and foundation insulation, air sealing, electric baseload measures or appropriate ventilation," she told MichiganScience. "The primary focus is on achieving the maximum energy savings possible in the home with the dollars available."