TORONTO - Premier Dalton McGuinty is defending a plan to saddle homeowners with a mandatory $300 energy audit as part of his Green Energy Act, dismissing critics who say this is yet another way to tax overburdened residents.

Forcing people to conduct audits is a good idea, McGuinty said, because it will allow buyers to know their energy costs.

"When it comes to buying the single most expensive thing that you're likely to buy during the course of your lifetime -- a home -- you're entitled to know what kinds of costs you're going to incur when it comes to energy," McGuinty said.

"We want to make sure that you can compare one house to another on an apples to apples basis."

Ontario realtors, however, said the additional costs will hurt homeowners in what are increasingly difficult economic times.

"The results of these audits will be used by home buyers as bargaining chips to significantly reduce the final selling price," said Gerry Weir, president of the Ontario Real Estate Association.

"Home sellers are already worried about lost equity in their homes. A move like this, which will reduce their value even further, will not help them in any way."

The group also notes there isn't one standard for energy audits and no regulation of auditors.

"The question that immediately came to my mind is: what then? After you do the energy audit, what happens?" asked Mel Fruitman of the Consumers Association of Canada.

"Is it to tell you you have to put another $20,000 into insulating the house or the government won't let you sell it?"

Progressive Conservative critic John Yakabuski said the mandatory audits will simply mean more stress for homeowners.

"I know all kinds of people in my riding and in various parts of the country where they're selling their home because they're forced to sell it because they can no longer make the payments," he said.

"The cost of having to do a $300, $400, $500 energy audit at a time like that amounts to another tax on the sale of their home."

The Liberal government said it will be up to sellers and buyers to decide who pays for the audit, noting that many aspects of the act are up for debate and improvement.

Energy Minister George Smitherman said the government will continue to provide a $150 credit to put toward the audits, since that's a "really crucial part of the incentive to try to assist people to have that information."

"It seems to be a pretty good piece of information to know, how much electricity the home is going to use," Smitherman said.

"If it has the effect of putting some positive emphasis on homes that use relatively less energy, that would seem to be an appropriate reward for the investment that people would make."

He also dismissed concerns from Progressive Conservative critic Joyce Savoline over provisions in the act that she believes will allow government inspectors freer entrance into homes if they don't think the audit was done properly.

Savoline said the details on the enforcement of the audits aren't clear, and she wants to know what changes could be in store for homeowners.

"People can be prone to all kinds of wild hyperbole," Smitherman said.

"This is an example of why we're about to have a legislative debate about these matters."

The act, introduced Monday, promises to streamline project approvals, mandate more efficient appliances, and provide low-interest loans to homeowners who wish to build their own small-scale wind or solar projects.

Critics say the legislation can only go so far without specifics such as targets for green energy or a move away from nuclear energy.