According to the group of inspectors the palace is Britain's largest "central heating radiator".
Other environmentally-unfriendly buildings on the groups list include the home of the Department of Environment, the Treasury and the Ministry of Defence.
Meanwhile, the HSBC building in Canary Wharf was names as the most energy efficient building in the country.
Buckingham Palace spent £2.2 million on utility bills last year, according to the National Audit Office.
In 2007 the Royal Family cost the British taxpayer £40 million.
Spokesperson for Campaign group Repulic told the BBC: "Clearly there is an urgent need to reform the way the monarchy is paid for."
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