A study to create the world's first evidence-based guidance for sustainable cooling strategies for vulnerable people during heatwaves has been launched.

Keeping cool during a heatwave is not just inconvenient, for many Australians it can be a matter of life and death.

Yet advice from public health agencies is severely lacking and fails to protect those most vulnerable, according to researchers who have launched a study into sustainable cooling techniques during heatwaves.

As Australia sweltered through its hottest month on record in January, scientists at the University of Sydney had just begun a recruitment drive for research on how older Australians can stay safe when the mercury rises.

The study, funded by the National Health and Medical Research Council, began testing on its first two participants last week, with researchers hoping to sign up about 100 Australians aged 60 or above by the end of 2019.

Lead researcher Associate Professor Ollie Jay says the increasing threat of heatwaves, which are Australia's deadliest natural disaster, particularly affects older people and those with cardiovascular disease due to their reduced ability to sweat.

Staying cool may seem simple, but one quarter of Australians do not have air-conditioners and many more struggle to switch them on due to the cost of energy bills, he said.

Meanwhile, an electric fan uses around 50 times less electricity than an air conditioner, while peaks in air-conditioning use risks overloading electricity grids and causing blackouts which leave even more people at risk.

Under careful medical supervision, study participants will be exposed to various heatwave conditions and cooling strategies while scientists measure core temperature, monitor the heart and measure dehydration.

Conditions will be modelled on events such as the dry Adelaide heatwave in 2009 and the humid heatwave of Europe in 2003, which led to tens of thousands of deaths.

Testing will take place at The University of Sydney's Thermal Ergonomics Laboratory in Lidcombe, in Sydney's west, and participants will each undergo four simulations that last three hours.

Researchers will explore the effectiveness of applying water to the skin, as a cooling technique, alongside moving air in different ways through modifications of fan speeds and direction.

They will also investigate hydration strategies: how much water do you have to drink, and does it matter what temperature the water is when you drink it?

"It's not an obvious one," said Assoc Prof Jay, director of the laboratory.

"When you drink an ice slushie, you reduce how much you sweat and get less evaporative heat loss."

The study is the first in a five-year research-series to develop evidence-based guidance on heatwave policies in a bid to improve public health guidelines.

The series follows findings from a previous study, from the same laboratory, which challenged current public health advice that cautions people not to use fans when temperatures rise above 35C due to extra heat on the body from convection.

"The message is oversimplified," Assoc Prof Jay told AAP.

"It's dependent on the ability of someone to sweat as it's the evaporation of the sweat that cools you down."

Assoc Prof Jay said the study, which will also take place at a university in Canada, could help reduce greenhouse gas emissions, which contribute to climate change.