The party says new research suggests those in rural areas living in fuel poverty will be £450 poorer than their urban counterparts when prices rise in October.
According to the Lib Dems, the average “fuel poverty gap” – the amount needed to lift households from the fuel poor threshold – is estimated to rise to £1,050 in rural areas when the price cap goes up.
This compares to a projected £600 in urban areas.
The party is calling for the new Prime Minister to offer extra support with energy bills to people living in rural communities, as they risk becoming the “forgotten victims” of the cost-of-living crisis.
This includes additional help for off-grid homes reliant on heating oil, which is not subject to the energy price cap.
It comes as Liz Truss is expected to tell MPs on Thursday that domestic bills will be frozen at around £2,500 as part of a package to ease the cost-of-living crunch.
Ahead of the announcement, she said: “We will take action immediately to help people and businesses with bills but also take decisive action to tackle the root cause of these problems, so that we are not in this position again.
“We will set out our plans to deliver on that promise and build a prosperous Britain for everyone.”
The Lib Dems’ rural affairs spokesman, Tim Farron, said: “The Conservatives have had months to set out a plan to tackle soaring energy bills. Instead families and pensioners have been left worrying day and night about how they will get through the winter.
“Families in rural communities are set to be hardest hit by this tsunami of soaring heating costs.
“The new energy package must take into account the rural fuel poverty gap and provide extra targeted support for those who need it. That must include those in off-grid homes who rely on heating oil or other energy sources.
“People living in the countryside are fed up with being overlooked and taken for granted by the Conservatives. Rural households must not be allowed to become the forgotten victims of this energy crisis.”