By Katherine Salant
Saturday, February 21, 2009
Most of the discussion about energy efficiency has focused on new construction and major renovations. Now it's time to shine the spotlight on existing houses and their often abysmal energy-use profiles.
Houses built to the standard of the most recent building code revisions -- the 2006 International Energy Conservation Code -- are reasonably energy efficient. But the efficiency of the roughly 80 million built before then ranges from acceptable but not great to marginal to truly awful when you get to the millions of houses built before 1970. Antiquated, nonexistent or inadequate energy saving measures can send as much as 50 percent of a household's heating and cooling energy directly to the great outdoors.
To get a sense of the enormous differences in energy consumption between old and new houses, take a look at their Home Energy Rating Systems (HERS) scores. The Energy Department uses HERS scores to determine Energy Star qualification for new houses.
A house built to the 2006 International Building Code standards will receive a HERS score of 100. A house with a HERS score of less than 100 uses less energy and is more efficient. To qualify for the Energy Star rating, a new house must score 85, which means it's 15 percent more efficient than that standard. A house built before 1970 will often have a HERS score of more than 200, which means it uses more than twice as much energy as the 2006 house, and a house built to the standards of the 1980s and '90s will often score between 130 and 140, said Nate Kredich of the U.S. Green Building Council.
What is the best way to address this problem?
You might assume that it's getting a new furnace or a condenser for central air conditioning, especially if your house is 30 years old and still has the original heating and cooling equipment.
But green building experts urge you to start with the low-hanging fruit and your "building envelope," or all the surfaces exposed to the outside. First, get an energy audit of your house from an energy specialist. (For more on this, go to Home Improvement at the Energy Star Web site, http://www.energystar.gov.) Some things can be done by handy homeowners, but many require professionals.
Every hole in the wall, including those for light switches, outlets and ceiling light fixtures, is an opportunity for air to get in and out. As much as 25 percent of your heating and cooling energy can be lost through these often tiny, pinhole-size leaks.
"In 99 of 100 houses in the U.S. on a cold, windy day, you can put your hand in front of a light switch or outlet and feel cold air coming in," said Ron Jones, editorial director of Green Builder magazine and a life member of the National Association of Home Builders board of directors.
Green building consultant David Johnston and his wife lit lots of candles for their first dinner party after moving to Boulder, Colo., in 1993. Within five minutes, drafts in his 1972 house had blown them all out. He began addressing the problem the next week.
Air leaks in the walls can be plugged with caulk or an expansive foam sealant, Johnston said. The cold air streaming in around the doors and windows can be eliminated with a combination of caulk and weatherstripping. This is one cure that most homeowners can do themselves.
The duct system used with forced-air furnaces and central air conditioning can also have leaks. These can account for as much as 25 percent of total household energy consumption. In older houses, the ducts can be sealed from the inside, using special equipment that sprays a liquid resembling latex paint, Johnston said.
The next item on your home energy checklist should be the energy lost or gained through your walls. Start in your attic; the greatest amount of heat can be lost there because hot air rises, Johnston said. Adding insulation here will make a huge difference during the summer as well as the winter. When the sun beats down on your roof in the hot season, the attic can get up to 140 degrees.
If your attic has ducts running through the roof truss rafters, they should be insulated as well. If it gets hot where you live, you can also benefit from adding a radiant barrier -- essentially a sheet of mylar -- to the underside of your roof rafters or the top chord of your roof trusses. This will also reduce the amount of heat passing through your roof to the attic space below.
The next stop is your basement or crawl space, Johnston said. A common complaint from owners of older houses is cold feet in winter because the underside of the floor in the main living areas is not insulated. The cure: insulation. If you regularly use your basement as a rec room or a home office, you should also insulate the walls and floor, Johnston said.
The last place to check for thermal heat loss is your walls. In the likely event you need more insulation, the solution is blown-in cellulose, made from recycled newspapers. As with the duct sealing, you will need to engage a professional with special equipment to do this.
Once you've plugged the air leaks and added insulation, your house may be so airtight that you need to bring in fresh air mechanically. The simplest solution is a small vent with a flap coupled with a continuously running exhaust fan in a bathroom to pull the air through the house and expel it. If this is inadequate, you may need an air exchanger, a device that pulls in fresh air while it exhausts stale air. In cold climates, a more sophisticated heat exchanger extracts the heat before exhausting stale air and transfers it to the incoming air.
With the air leaks plugged and the heat loss and gain stanched, you may find that you don't need to replace your furnace or condenser for your central air conditioning. But if you do, you may find that smaller and less costly models will do the job because you don't need as much heat or cooling to keep your home comfortable.
A final word of caution. Weatherization measures can make the air pressure inside your house lower than outside, which can cause your gas furnace to backdraft -- that is, the exhaust fumes may be pulled back into your house instead of being expelled up the flue. The cure for backdrafting can vary from house to house; to learn what is appropriate for yours, consult a professional home heating specialist.
Katherine Salant can be contacted via her Web site, http://www.katherinesalant.com.
© 2009 Katherine Salant