A new report from St Vincent de Paul says the capital's "dual fuel" households, many of whom use gas to heat their homes, can expect to pay nearly $115 more annually, even after the removal of the carbon tax.

St Vincent de Paul also warned that gas bills in the ACT and NSW would continue to rise for the next two years.

The blow was softened by the post-carbon tax prices announced by ActewAGL on Wednesday, but St Vincent de Paul’s director of research, Gavin Dufty, said the higher gas charges kicked in from the end of July, just in time for Canberra’s coldest snap for several years with temperatures plunging past minus 7 degrees.

With Wednesday’s new pricing structure announced by ActewAGL, the figures have been revised: electricity-only consumers will find themselves about $100 ahead while dual-fuel users will pay an extra $115.

Mr Dufty said events overseas, such as the shutdown of much of Japan’s nuclear power network, had increased demand on Australia’s domestic supply, pushing up wholesale prices which were then passed onto the consumer.

“What you’re seeing is the increase in gas costs being passed through and that is having a significant contribution to the cost of those dual-fuel households,” Mr Dufty said.

“Domestic natural gas is starting to be shipped offshore which means there is less gas in the domestic market and that is starting to drive up the cost of gas.”

Mr Dufty said it was unclear how much of the increase had been imposed on the retailer but said the real problem for ACT consumers remained the lack of competition in a local power market dominated by ActewAGL and minority competitor Energy Australia.

“We don’t know the details, whether there’s a bit of a gouge in there, but what we do know in Canberra is that you’ve got no options,” Mr Dufty said.

“You don’t have much competition, some would say none, so that’s the price.

“One of our concerns is that people can’t shop around.”

He warned that the upward trend in the gas price was here to stay in the medium term.

“People should brace for further increases in the next two years, and NSW and ACT are particularly at risk,” he said.

Mr Dufty also warned that ActewAGL’s approach to carbon pricing, paying some householders back some of the money they had already paid, was a recipe for confusion.

“There is going to be mass billing confusion,” he said.

“The way they’ve done it is incredibly confusing.”

A spokesman for the power retailer said on Wednesday that some customers would get a new bill while other would receive credits.

“Customers who have already received a bill between 1 July and 31 July, 2014, will have a new bill issued based on the new carbon-exclusive prices,” the spokesman said.

“Customers who have already paid their bill will receive a credit for the carbon amount which will appear on their next bill.”