Robert Whale knew his 1920s Sears Roebuck bungalow wasn't exactly airtight, but he didn't know just how drafty it was until an energy auditor flipped on the switch to a large fan he had placed in the doorway.

That buzzing coming from an upstairs bedroom? The sound of Whale's heating bills spiraling higher, by way of an air-conditioning unit that hadn't yet been stored for the winter.

The fan was part of a "blower door test," a tool often used in energy audits, in which inspectors analyze a house, looking for where energy is being wasted -- and ways it can be conserved.

Lately, consumer interest in such audits has grown along with concern about rising energy costs and the environmental impact that housing choices can have.

But are they worth the $250 to $500 price tag?

It can be money well spent, said Kateri Callahan, president of the non-profit group Alliance to Save Energy. "We recommend that people improve the efficiency of their homes -- whether they go all-out and hire someone or just do the work themselves."

Energy audits aren't new. Governments and utilities used to provide them or subsidize them, a practice that fell out of favor during energy deregulation, said Robert Dobkin, a spokesman for the Pepco utility company. For residential customers, "doing these things was left to the commercial marketplace," he said, though Pepco Energy Services still performs audits for commercial customers.

Local governments and utilities are experimenting with pilot programs offering audits; Arlington County, Va., for example, provided free audits to a limited number of homeowners this year.

A professional can point out things homeowners might not have thought of on their own, such as leaks around electrical outlets or just how much difference storm windows or Energy Star appliances can make.

"People don't always understand," Callahan said, and an audit can help them make better-informed financial decisions.

Professional auditors aren't the only source of information on improving energy efficiency. The Energy Department, for example, has an online tool called Home Energy Saver that walks consumers through largely the same process a professional auditor uses.

Whale said he hired Peter Van Buren, of TerraLogos, to help him prioritize some of the improvement projects he was considering for his Washington house.

While Van Buren questioned Whale about his family's daily habits and the age of various appliances, his co-worker Atticus Doman went from room to room with an infrared camera, scouting out signs of inadequate insulation and drafts.

Such inspections usually take two to three hours, and after they are complete, Van Buren compiles a list of recommendations to improve the home's efficiency, with an eye toward cost-effectiveness.

TerraLogos, of Baltimore, does not perform any of the upgrades, but it connects clients with prescreened contractors.

Residents of older houses usually reap the greatest benefits from energy audits, said Doris Ikle, president of CMC Energy Services, of Bethesda, Md., which sells the Home Energy Tune-Up software that many auditors use, among other energy consulting services.

But that doesn't mean new houses are perfect. "Even the new stuff can be pretty bad," Van Buren said.

Homeowners may not need to pay for every test to benefit. In particular, Ikle said she doesn't consider the blower door test worthwhile for every homeowner, given the cost it adds to the inspection. "You'll pay twice as much for the audit" if it's included, she said, and it will just have to be repeated by the professional leak sealer if you hire one.

Homeowners interested in hiring an energy auditor should use the same diligence they would in hiring any contractor, including checking references, Callahan said.