Workers at Canberra's 50 Marcus Clarke Street got an early visit from Santa and his helpers on Thursday as the rest of the city tried to beat the heat.
As the city's temperature hit 35 degrees, swimmers hit suburban pools and Lake Burley Griffin - just as staff from Touchdown Building Services used a regular window cleaning to spread some Christmas cheer.
Justin Ryan said the idea of cleaning windows in Christmas costumes had been months in the making.
Complete with three helpers, Santa made sure the sunshine could be seen from inside.
''We've been thinking about doing it for a year or two and we thought it would be a fun thing to do in the last few days before Christmas,'' he said.
''One of the excellent things about the job is you work with the sun and the season.''
Canberra was set to swelter through one of its hottest nights since last summer, with the city's night-time lows staying above 17 degrees on Thursday and Friday.
Heading for a top of 35 degrees and mostly sunny conditions on Thursday, the temperature reached the top about 5pm.
Meteorologist Ben McBurney from Fairfax-owned Weatherzone said: ''[Friday] is expected to be even hotter again, with an expected top of 37 degrees.''
Canberra's December average top was 26.1 degrees and evening temperatures would be high, he said.
''Friday night into Saturday is also going to be a very warm night when it could get down to 18 degrees.''
Saturday would bring a weak cool change and a top of 32 degrees, before cloud and 34 on Sunday.
Monday's forecast top is 31 degrees with possible showers.
''Christmas Day on Tuesday is looking like a pretty good day with mostly sunny skies and a top of about 26 degrees at this stage," Mr McBurney said.
The Bureau of Meteorology said on Wednesday that Australia is in the grip of its first heatwave of the summer, warning holidaymakers to stay hydrated and avoid prolonged exposure to the sun.
The slow-moving high-pressure system that brought blistering heat to Perth during this week's Ashes Test is now sending the mercury into the high 30s or low 40s across much of the continent.
Melbourne reached 40 degrees on Thursday, while Sydney hit 25 degrees with a forecast maximum of 28.
The ACT Rural Fire Service and ACT Fire and Rescue have extinguished a two-hectare grass fire burning at Paddys River.
An Emergency Services Agency spokesman said that seven fire units were conducting clean-up operations near the river at Point Hut Crossing.