The report, released on Wednesday by community group Better Renting, found renters are four times more likely to be unable to keep cool in the summer.

Renters are also between three and six times more likely to be living in "poor" or "derelict" housing than homeowners.

The report found people most at risk from extreme heat - including the elderly, people with mental illness and the socially isolated - are more likely to live in substandard housing, compounding their vulnerability.

"(They) have less capacity to adapt, and they are more likely to struggle with cooling costs," the report said.

"Renters are particularly at risk, partly because they are prevented from making structural improvements to their home."

The report details the accounts of renters too afraid of eviction to ask their landlords for better insulation, ceiling fans or other measures to beat the heat.

Melbourne renter Anna Thomas said her bedroom is uninhabitable during hot weather.

"I have to sleep on the couch or even outdoors, our landlord is so tuned out it's not even worth asking for better insulation or cooling," she said.

Emily Buster, who lives in an older house south of Brisbane, said she resorts to "spray bottles, floor fans or heading out of the house for most of the day" in an effort to keep cool.

Better Renting executive director Joel Dignam said renters are at greater risk of heart, lung, and kidney ailments due to climate change, as well as mental health challenges.

"Heatwaves are Australia's deadliest natural hazard and are being made worse every year by climate change," he said.

The report urges the government to update energy and sustainability requirements for new and existing homes, improve access to public "cool spaces" such as air-conditioned libraries and make it easier for everyone to access solar energy.

While there are no regulatory structures to compel landlords to install airconditioning, Real Estate Institute of Victoria president Leah Calnan said many are willing to discuss installing it with their tenants.

"There are always options available people sometimes just get caught up worrying it is how it is and nothing's going to change, but everyone landlord is different," she said.

Ms Calnan said the price of a rental generally increases by $10 to $15 a week for airconditioning, but also suggested other methods to keep cool.

"Particularly for apartments without a balance to install airconditioning, it's about looking at your insulation, your window coverings," she said.

Victorian and NSW tenants will soon be able to make some minor modifications, such as installing blinds, to rental properties without their landlords' written consent under new laws in those states.

The definition of urgent repairs, to be paid by landlords, has also been widened in Victoria to include repairs or replacements relating to air conditioning.

Other states including Queensland and WA are considering rental reforms.

Australian Associated Press