The ideal temperature to turn on the heat depends on personal preference, but there are some general guidelines to follow. The World Health Organization recommends that regular people keep their homes at 64.4 degrees Fahrenheit or higher, while for those who are young or old (or who have an illness), it recommends a minimum indoor temperature of 69.8 degrees Fahrenheit. The Department of Energy suggests turning on the heat when the outside temperature falls below 68 degrees Fahrenheit to save on energy bills. However, it is important to note that these are just general guidelines, and the decision of when to turn on the heat ultimately depends on personal preference and comfort level. Some people may turn on the heat when the outside temperature drops below 60 degrees Fahrenheit, while others may wait until it drops below 50 degrees Fahrenheit. It is also important to consider factors such as insulation and draftiness of the home when deciding when to turn on the heat. Ultimately, the decision of when to turn on the heat is up to the individual, but it is recommended to keep the indoor temperature between 64 and 75 degrees Fahrenheit to keep people healthy who are wearing suitable clothing.