Sharing a wall or two is just a good start, though. In the meantime, there are measures you can take to further stiff the gas man without even leaving the house.
For instance, you can save around 1 percent on heating costs for every degree you lower the thermostat (for at least eight hours a day), according to the Philly-based Energy Coordinating Agency (ECA), which has been raking in federal, state and private grants to help weatherize homes and train people in "green-collar" jobs. That means lowering the thermostat from 70 to 65 saves about 50 bucks for every $1,000 of heating bills.
THAT'S to say nothing of sealing off the third floor that's never used, or letting Junior's bedroom - empty because he's off at college overheating his dorm room - get a little chilly while you stay a little cozier.
Cleaning or replacing air filters works wonders, too. Of course, the proactive approach (spending a little up-front) will work even better, so while you're at it, get your ducts in a row.
In homes with warm-air heating, the ducts often leak as much as 20 percent of the air that comes through, the ECA says, meaning more dust and humidity for living spaces. It could cost you some money for a thorough duct cleaning (low three figures), but at 15 to 20 percent in immediate returns on monthly bills, it'll pay for itself by midwinter.
By adding certain devices to your heating system, from the simple (a flue or damper) to the high-tech (modulating aquastats, which adjust the temperature of hot-water heating depending on the outside temperature), hundreds of dollars can be saved each year, even in small homes.
And did you hear that PECO is giving away money? The utility offers $250 to $400 for homeowners who install Energy Star heat pumps, which provide heating and cooling from a single source. Some central air-conditioning units qualify for rebates, too.
PECO will also pay you to take away your old wattage-wasters ($35 for a working fridge or freezer, $25 for a window AC unit). For new stuff, their rebates range from $75 to $400.
Energy-efficient windows, doors and skylights get a $3.75 per square foot rebate, and new insulation earns you 50 cents a square foot, among other incentives. Go the whole nine and convert to a natural-gas furnace or boiler and you get $200 back.
Further, whether you're a conservationist or a conservative (or both), chances are you'll enjoy getting some cash from the government - Harrisburg and D.C.
There's a federal tax credit of 30 percent (up to $1,500 - but it expires Dec. 31) for energy-efficient home heating, ventilating and air-conditioning units, furnaces, boilers and insulation materials, and some roof products.
For heat pumps and solar panels, the 30 percent tax credit has no upper limit.
The commonwealth offers a $1,000 rebate for high-efficiency heating and hot-water systems.
Too busy trying to find a job to worry about greening your crib? Take a minute to look at ECA's Weather Assistance Program, a complete energy conservation program for low-income households. The goal is to save these homes between 20 and 40 percent on energy bills, enough to put a few more presents under the Christmas tree.
All of this info and more can be found on the ECA Web site at www.ecasavesenergy.org. The Philadelphia City Planning Commission also has a 52-page guide for rowhouse owners, at www.philaplanning.org/pubinfo/rowhousemanual.pdf.
No matter what type of house you have, city or suburb, rendering it energy-efficient makes as much sense as getting your own body in shape. The short-term benefits are swift and the long-term rewards steep. But there will be no ads for this stuff on "Monday Night Football." So be like Nike. Just do it.
Thomas J. Walsh is a local writer. Contact him at firstname.lastname@example.org.