Stimulus funds for simple home upgrades will give us the most bang for our billions"The most important high tech tool of the new green economy," Van Jones likes to say, often pausing for dramatic effect, "is the caulk gun." Not photovoltaic panels or wind turbines, not lithium batteries or advanced biofuels, but the tool you can get for $17.99 at Home Depot. Considering the enormous potential for energy savings in the retrofitting of America's housing stock, it's a hard point to argue.Energy efficiency is surely the lowest hanging fruit in the quest to satisfy our national energy hunger (and to cure our addiction to oil)-household energy use totals about 22 percent of our nation's total energy consumption, much of which is senselessly wasted through poor design and construction. And of the easy to reach fruits of efficiency, the very easiest to pluck might well be the weatherization of homes, which Amory Lovins, efficiency guru and founder of the Rocky Mountain Institute, once called the "oil field in our attics."What's great about weatherization is that we already know how to do it, we've got all the tools it takes-it doesn't depend on any breakthrough technologies of the future-and it's pretty cheap. Less than cheap, actually, as projects to better insulate and seal homes generally pay for themselves in less than a decade.Proper weatherization does, of course, take more than just a caulk gun. Just about anybody could do the basics on their own-caulking windows, tacking weatherstripping on the bottoms of doors, installing storm windows and doors in the winter-but the leaky sieves that pass for houses in this country could generally use a more thorough retrofit by trained professionals. Which brings us-as does just about everything these days-to the economic stimulus.If you're looking for a way to invest money in programs that create jobs and put money in the pockets of hard-up Americans, you can't do much better than weatherization. And, actually, for 30 years now, the Department of Energy has run a "Weatherization Assistance Program" that's retrofit over 5.6 million low-income homes. Any eligible household can contact their local weatherization agency (funds are channeled through state programs, and states identify qualified agencies-most are non-profits that hire energy professionals), an auditor comes and assesses the building, then workers arrive, blowing in insulation, repairing heating and cooling systems, sealing ducts, and so on. The work takes a day or two. The whole process costs the government about $2,500 on average.For residents, the program's benefits are clear-the typical house that's taken advantage of this publically-funded weatherization service sees a 32 percent drop in gas or oil heating energy consumption, a savings to the tune of about $350 every year. For the low-income American families that spend about 16 percent of their income on energy costs (the national average is 5 percent), this is a significant chunk of change.The public benefit is tougher to figure, but it's real. Weatherization creates good jobs locally and keeps dollars in the community, it lowers the overall cost of heating fuels by lowering demand, and it cuts carbon emissions and reduces our dependence on oil. The DOE has run some calculations (pdf)-ones that I won't pretend to fully understand-that plainly state that for every $1 invested in the program, weatherization returns $2.60 in energy and non-energy related benefits.Last year, the Weatherization Assistance Program served about 140,000 homes with a budget of $250 million. The problem is, the DOE estimates that there are nearly 34 million homes eligible for weatherization funds. So at the current rate, it'd take roughly 243 years to reach every house that could use a better seal. With the passing of the stimulus bill, however, the program gets a $5 billion shot in the arm, with the aim of achieving President Obama's stated goal of weatherizing one million homes every year.Answering criticisms from the right that these funds were nothing more than pork-barrel spending, Obama bluntly rebutted: "We're going to weatherize homes. That immediately puts people back to work. And we're going to train people who are out of work, including young people, to do the weatherization. As a consequence of weatherization, our energy bills go down and we reduce our dependence on foreign oil. What would be a more effective stimulus package than that? I mean, you're getting a three-fer. Not only are you immediately putting people back to work but you're also saving families on your energy bills and you're laying the groundwork for long-term energy independence. That's exactly the kind of program that we should be funding."Very soon, funds will stat to pour into various programs as designated by the stimulus plan, much of which will go to various "green recovery" projects. And while futuristic high-speed trains, smart grids, and wind farms will get most of the attention, the simple, cheap, and decidedly 20th century technologies of weatherization promise to yield the most immediate bang for our few billion bucks.