Public Health England has cut the recommended temperature that people should heat their homes to from 21 degrees C last winter down to a minimum of 18 degrees this year, opening the way to families reducing their bills by turning down the heating.
It says the change follows a full review of the available science.
As householders start to turn on their heating, there can be uncertainty, even arguments, over where to set the thermostat.
It's not just a question of comfort, it's important for health and for the bank balance because of the high cost of gas and electricity.
Last year Public Health England said rooms occupied during the day should be kept at a minimum of 21 degrees celsius and at 18 degrees at night.
But when the government body checked the evidence this year, it found that the guideless were based on outdated World Health Organisation figures from 30 years ago.
A fresh review has resulted in a lower recommendation of at least 18 degrees, day or night, which they say poses minimal risk to the health of a sedentary person, wearing suitable clothing in winter.
Below that the danger of stroke or heart attack begins to increase.
They do add that the over 65s and those with medical conditions may benefit from a slightly higher temperature.
Savings from turning down the thermostat by 3 degrees could be substantial.
British Gas says a reduction of just one degree could cut the typical gas bill by as much as 10 per cent.