Depending on where you live, sometime between 4 a.m. and 7 a.m., it’s the first day of winter. And, as the temperatures plummet, your thermostat numbers head due north, generating hefty utility bills that could put you out on the street. There are, however, ways to regain control. Here’s how to cut back on money lost and to reduce your home heating cost. Surely you’ve noticed that natural gas is up 8 percent from last year. Heating oil is worse yet — about 18 percent. Electric heat is up, too. To fight back, start with the basics: Plugging air leaks and adding insulation saves as much as 20 percent. Turn down the heat — each degree saves 3 percent. Put an insulating wrap around your water heater, and cover hot-water pipes with foam tubing. Caulk and weather-strip cracks around windows and doors, and change furnace air filters.