The maximum temperature in Canberra is due to hit 39C on Wednesday, Thursday and Friday, according to the Bureau of Meteorology.

The seven-day forecast on Tuesday afternoon showed little relief in store for the capital, with a maximum temperature of 28C on Monday tipped as the week's lowest.

In the lead-up to the heatwave ACT chief health officer Paul Kelly encouraged Canberrans to stay hydrated, remain inside in an airconditioned environment whenever possible and to never leave children or pets in cars unattended.

Dr Kelly said he was concerned about elderly and low-income residents who felt it was too costly to cool their homes and encouraged them to head to shopping centres to take advantage of the airconditioning.

ActewAGL general manager network services Rob Atkin said if residents had received a letter regarding power outages this week the maintenance work would go ahead, regardless of the high temperatures.

There were several planned outages across Canberra this week, including in parts of Charnwood, and crews would be sent out as early as possible to try to finish the work before the hottest part of the day.

''Planned electricity interruptions are an essential part of ActewAGL's maintenance program, which is required so we can ensure the reliability of our electricity network and prevent potential issues which may cause unplanned electricity interruptions in the future,'' Mr Atkin said.

Meantime one of the country's pre-eminent climate change experts has said Australians who refuse to acknowledge the connection between global warming and the increased frequency of severe heatwaves need to pull their heads out of the sand and look at the facts.

Australian National University adjunct professor Will Steffen said the link between climate change and extreme weather was beyond reasonable doubt and denial would only lead to Australians suffering through more periods of extreme heat.

''We have to acknowledge the nature of them, how they're changing, that means we can be better prepared for bushfires, heatwaves, high-sea-level events and so on,'' he said.

Professor Steffen said reducing carbon emissions would help avoid leaving an even more unstable climate for future generations.

''As we put more greenhouse gases in the atmosphere we're trapping more heat near the earth's surface, it's a simple physical fact, it's been known for nearly a couple of hundred years,'' he said.

''As we trap more heat near the earth's surface it simply loads the dice, stacks the odds towards more hot weather, more heatwaves, longer heatwaves, higher temperatures during heatwaves.''

Mr Atkin said Canberra's peak electricity usage on Tuesday was 510 megawatts at 3.30pm and was expected to rise.

On Monday peak electricity usage was 485 MW at 5.30pm, significantly less than last summer's peak of 700 MW at 4.45pm on January 18, when the temperature was 42C.