It seems that if you close the door to an unused room, you can avoid paying to heat it, right?
The opposite is true. When you close off an interior room, or if you close the air vents in that room, your heating system has to work harder and can even break down as a result.
The reason: Your home’s HVAC system is designed to keep the whole house comfortable by distributing heat evenly throughout. If you close off a room or a duct, you reduce the airflow to that room and force your system to work harder to heat it up.
That can cause a pressure imbalance, which can damage your ducts or your heating system.
Here’s a better idea: Save money and energy by using caulk to seal air leaks around windows and holes in walls where cables enter the house. Add insulation to the attic. Install curtains that are thermally insulated. Replace your outdated thermostat with a programmable one that will lower the temperature at bedtime and when everyone leaves the house in the morning.