As combined utility bills cost up to £1,400 a year, the advice service has also estimated that collectively homeowners are spending around £70 million annually by being on the tariffs.
David Kuo, head of personal advice at the website, said: "The expense in moving can be made more costly if consumers unsuspectingly sign up to penal energy tariffs.
"New occupants should not delay in switching away from deemed tariffs, even if it means transferring to a monthly direct-debit tariff with the same lender first."
A recent study by Alliance Trust found that people over 75 are the age group hardest hit by the rising cost of food and energy in the UK.
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