What preventive measure is essential for winterizing a water heater?

Draining the water heater is the essential preventive measure for winterizing it. This procedure ensures that any residual water within the tank is removed, reducing the risk of freezing and subsequent damage to the water heater during colder temperatures. When water freezes, it expands, which can lead to cracks or ruptures in the tank and plumbing connections, ultimately resulting in costly repairs.

While other measures might support overall efficiency or maintenance, they do not directly address the critical issue of freezing water. For example, adding insulating foam can help with energy efficiency but won’t prevent the freezing of water inside the tank if it is not drained. Removing the check valve or installing a new valve may be relevant for other maintenance tasks or upgrades but do not directly contribute to winterizing the system against freezing. So, draining the heater is the most vital step to safeguard against freezing damage during winter months.