Royal officials have been criticised after 25 windows were left open at Buckingham Palace.
TaxPayers' Alliance chief executive Jonathan Isaby compared last week's mistake when temperatures plummeted to -3 degrees to burning cash in a fire.
It reportedly costs £1.1m a year to heat the 775 room palace.
"Closing windows on cold days is just common sense. Taxpayers don't have bottomless pockets," he told The Sun.
A spokesperson for Buckingham Palace said some of the windows on the top floor were left open during maintenance work and redecorating.
The union flag was also flown at half-mast at Buckingham Palace following the death of King Abdullah of Saudi Arabia which provoked controversy last week.
Top five facts on Buckingham Palace
Buckingham Palace has 775 rooms. These include 19 State rooms, 52 Royal and guest bedrooms, 188 staff bedrooms, 92 offices and 78 bathrooms.
Buckingham Palace gets its name from eighteenth-century Tory politician, John Sheffield, 3rd Earl of Mulgrave and Marquess of Normanby, who was created Duke of Buckingham in 1703. He built Buckingham House for himself as a grand London home.
In 1761, George III bought Buckingham House for his wife, Queen Charlotte.
There are 1,514 doors and 760 windows in Buckingham Palace.
The Prince of Wales, The Princess Royal, The Duke of York and Prince William were christened by the Archbishop of Canterbury in the music room of Buckingham Palace.
There are more than 350 clocks in Buckingham Palace, one of the largest collections of working clocks anywhere.