Some 400,000 households in England – many of them including vulnerable older people – face energy bills of up to £4,679 a year, experts warn.
These households are not protected by the energy price cap and need urgent help, the National Housing Federation (NHF) has said.
The affected homes are on communal networks and have their heating supplied through a central boiler that reaches all homes in a building, rather than having an individual boiler in their home.
They pay for their heating bills with service charges.
Heat networks usually save residents money, as housing associations can secure cheaper prices than individuals on domestic contracts by bulk buying energy.
However they are not regulated by Ofgem , which sets the domestic gas and electricity price cap.
Without the domestic cap, the price these people will pay for energy will depend on the commercial contract their housing provider negotiates with the energy company.
Average energy bills will soon set to hit £3,549 a year as regulator Ofgem raises its price cap in October.
But the NHF said recent quote for homes on communal networks were as much as 500% more expensive than the previous year..
Some bills for low-usage homes are set to rise by as much as £1,130 per year more than October’s energy price cap - to £4,679 a year.
The NHF said a large proportion of people on communal heat networks lived in supported or sheltered housing, a form of social rented home for people on low incomes with support needs.
Some 72% are vulnerable older people over the age of 55.
The Government confirmed earlier this month that residents on heat networks will now receive the £400 energy rebate, although it is yet to be confirmed how this will be administered.
Many housing associations are trying to find ways not to pass these energy bills on to residents.
But many not-for-profit and so cutting energy bills means scaling back on other services for residents or reducing investment, the NHF said.
The NHF is calling on the Government to act urgently to ensure people on heat networks receive the same protection as customers on domestic energy deals.
NHF chief executive Kate Henderson said: “It is unjust that hundreds of thousands of people, through no fault of their own, are exposed to uncapped heating bills just because of the way they pay for their energy.
“Worse still, the majority of those affected are vulnerable people on the lowest incomes in this country, who will already be struggling to pay for food and essentials.
“With the price cap coming into force in October, it is essential that the Government acts now and negotiates with energy companies to ensure every resident is protected from rising energy bills.”
