He steps into the role as the service faces significant structural change, joining fire and rescue and the State Emergency Service in government plans to overhaul the emergency services to improve efficiency, reduce costs and eliminate duplication.

The new acting chief officer of the ACT Ambulance Service, Jon Quiggin, said a lot had changed since he was a paramedic but he was eager to return to Australia's "best-performing" ambulance service.

A Productivity Commission report published last year found the ACT Ambulance Service had the fastest response times in the country. Half of critical cases were responded to within eight minutes.

"I'm looking forward to working with staff at all levels to ensure we continue that pattern," Mr Quiggin said.

"The big thing [for me] is just getting to know the staff, learning what are some of the issues and collectively figuring out ways we can improve it."

Mr Quiggin has held senior government roles, including with the ACT Commissioner for Fair Trading.

Reflecting on the challenges the ambulance service faced, Mr Quiggin said increased demand would have to be managed, in line with the ACT's rising population.

The changes he had noticed since he left after 19 years with the ambulance service were an increase in demand, as well as improved "clinical capability".

Mr Quiggin took the opportunity on his first day in the job to warn Canberra residents of the hot week ahead as temperatures were expected to peak in the high 30s.

He advised people to prepare for the heat, especially if they were working outside, and make sure they drank enough water and sought shade.

Mr Quiggin would act as ambulance chief until recruitment for the permanent role finished this year, an Emergency Services Agency spokesman said.

Advertising for the role is due to begin in February.

Long-serving former boss David Foot has moved into a new role as director of risk and planning.