When Jan Wetterer of Adelphi decided her big colonial house needed insulation, she sent in a postcard that had come with her Washington Gas Light Co. bill offering a free home insulation estimate.

But after listening to the gas company insulation salesman and checking with federal energy experts, Wetterer was left feeling confused about the whole subject. She even felt she had been "misled" by the WGL insulation salesman.

Although she and her husband plan to go ahead and do some insulation work themselves, Wetterer said, they are not really sure how much money it will save them in reduced utility bills.

The Wetterers are not alone, like thousands of other homeowners in the Washington area and across the country face with the rising utility bills, they are asking: What energy-saving improvements - such as insulation - should we make in our home? How much will they cost? How much money will they save us?

There are no easy answers to these questions.

Although the national energy legislation passed by Congress last week requires utility companies to offer to inspect their customers' homes and then "arrange" for contractors to install appropriate energy-saving measures and for financial institutions to make the necessary loans, these programs are not expected to go into effect until sometime in 1980.

Meanwhile, the Wetterers and other homeowners are left to fend for themselves amid a confusing welter of possibilities and conflicting claims in the growing marketplace for home insulation and other energy-saving devices.

In dealing with the local gas company and federal officials here, Wetterer learned some important first lessons:

WGL views its home insulation program as strictly a money-making, business proposition. The salesman who visits your home is there to sell insulation, not to perform the kind of comprehensive "energy audit" of the home contemplated in the new national legislation.

Except where the homeowner is exceptionally well informed, only such a comprehensive "energy audit" performed by an expert who records and analyses pertinent details about the house and family life style can indicate with precision what measures should be taken and how much they will save in reduction utility bills.

While federal energy experts can send you booklets on insulation and other energy-savers and can give general advice over the telephone, the generalizations may not work for your particular home and family.

Listen to Jan Wetterer:

"The problem was getting the facts. The salesman said we'd save 20 to 22 percent on our monthly bill . . . That sounded really good until I started calling around."

Finally, Wetterer said, a WGL officer admitted to her that the insulation the company has installed in 7,500 houses in the past three years saves between 7 and 38 percent on monthly bills, with an average saving of 21 percent. She said the salesman had not told her that.

"I figure that is unethical, to tell a person something will save 21 percent when it might be 7 percent," she said.

"I'd like to know that woman's name because I'd like to call up and apologize," said Ricard C. Vierbuchen, WGL's vice president for non-utility operations.

Vierbuchen said WGL's nine insulation salesmen are instructed to give not only the average saving but the range, and to point out that the amount of saving will depend on the type of house, living habits of the inhabitants and other factors.

The company began selling insulation three years ago in order to generate revenues in the face of gas shortages that caused a drop in earnings, according to WGL spokesman Paul Young.

The company salesmen are paid on a commission basis and make no effort to do a thorough "energy audit" of houses they inspect, according to Young and Vierbuchen. "They're insulation salesmen," said Vierbuchen. ". . . I don't think (they perform) as energy audit."

WGL's insulation group made a 1.6 percent profit on $1.3 million in gross revenues in 1977, Vierbuchen said. He said the average insulation job costs $630 and about 40 percent of the jobs are paid for on time, with payments being part of regular gas bills.

WGL acquired its main contractor, Davenport Insulation Inc, for $6 million and uses a second insulation firm under contract, Vierbuchen said.

In order to prevent anticompetitive practices, the new energy legislation prohibits utilities from doing the work themselves or providing major financing for it, both of which WGL now does. However, both WGL officers and sources in the U.S. Department of Energy said they expect the company's insulation program will be allowed to continue.

Young said the Federal Trade Commission will begin studying the program to see if it is anticompetitive. He also said WGL considers the insulation program separate from whatever the company may be required to do under the new legislation.

"We're talking about two distinct entities here," said Young. "We are stydying the impact of the law . . . Obviously what we have here is an interim period."

Vierbuchen said WGL's insulation program is "competitive" in price with private contractors.

Paul D. Ackerman of Boor Allen & Hamilton, a consulting firm that studied utility-sponsored insulation also said utility-sponsored programs are generally competitive in price with private contractors.

But Wetterer, as a homeowner, has been left a trifle uncertain by all of this.

By calling local supply stores, she said, she learned that she and her husband can save about half the $386 that WGL was going to charge her to insulate the attic simply by buying insulation and installing it themselves.

Vierbuchen said a customer can save about $100 by installing his own attic insulation. But he warned that a bad job could result in energy losses that could eat up the one-time installation saving.

Homeowners cannot easily install insulation in walls and some other areas themselves, Vierbuchen added.

Even if Wetterer installs insulation herself, she said, she is not sure how much it will save her.

She recalled telephoning a DOE man who told her that with several inches of insulation already in her attic, she mighbetter work on weather-stripping storm doors and windows and floor insulation first.

Gerald [WORD ILLEGIBLE] , a DOE engineer, told a reporter that what Wetterer recalls being told "sounds reasonable."

He said that if Wetterer had no insulation at all in her attic then maybe she could achieve big savings by insulating it, but that if she already had some there the savings might be minimal.

Lohsl said the National Bureau of Standards experimented with a house in Gaithersburg and found that adding storm windows reduced the heating requirement by 25 percent, insulating walls 20 percent, insulating the floor 8 percent, and insulating the attic - which already had several inches - only 6 percent.

"Houses are a lot like people," said Douglas Burch, an NBS engineer who worked on this project "It's going to be different for every house . . . This study gave a good indication that installing storm windows was more cost-effective than adding thermal insulation to the ceiling, walls and floors. But keep in mind that if the attic had been uninsulated to begin with then it might have been a different story."