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Energy savings can stretch only so far

Question: I'm confused about something. I was reading the labels on a bunch of products at a hardware store last week, and I saw that some of them save 10 to 20 percent in energy, some a little more and some a little less.

If I buy a few of these and use them all, can I cut my energy bill to almost zero by adding these numbers together?" How much can I expect to cut my utility bills if I use all of these products?

Answer: Nope. It doesn't work like that. You'll cut your bills a lot, but consider how. The reason is that all of these products interrelate. Using one or more of them affects the performance of others.

For example, if you have dark shingles on your roof, installing some attic ventilation will greatly lower all the heat that builds up in the attic, but, if you already have light-colored shingles, the ventilation won't make that much of an impact since the heat buildup is lower.

Further, you need to read the labels carefully to see exactly what type of savings the manufacturer is promising. You'll find that the package probably talks about savings in terms of the particular heating or air-conditioning load, not in terms of the total home's energy use.

For example, you might do everything you can to cut down on the heat that gets into your home through the attic: put on light-colored shingles, install an attic radiant barrier, insulate and vent the roof and attic areas.

You'll save a lot of energy this way, of course, but note that researchers have found that heat from the roof accounts for only 12 percent of the total load on an air conditioner. This means that, no matter how much you do to the roof, you can't cut your total bill by more than the 12 percent that comes from this source.

However, 12 percent is a substantial figure, so don't give up and say it isn't worth doing. Just keep in mind how much you can really control and try to find ways to save energy where it will do the most good. Researchers have found the following loads on air conditioners in Florida:

Humidity infiltration: 25 percent.

Interior-generated heat: 21 percent.

Windows: 19 percent.

Interior-generated humidity: 13 percent.

Roof: 12 percent.

Walls: 8 percent.

Heat infiltration: 2 percent.

In other words, if you seal up every crack, hole and other openings in your walls and cut the heat loss down to zero, you can expect to lower your monthly utility bill by up to 8 percent. If your bill is now $100 a month, that 8 percent savings will be about $96 a year, a lot more than you will spend for caulk to plug the holes.

Ken Sheinkopf with the Solar Energy Research and Education Foundation in Washington will answer questions about energy conservation and home comfort. Write to him in care of the Orlando Sentinel, P.O. Box 211, Orlando, FL 32802-0211.