The answer to 'why is my water heater blowing cold air' is that your water heater is likely not functioning properly and needs repair or replacement. This could be caused by a variety of issues, such as a broken heating element, a faulty thermostat, or sediment buildup in the tank.
Some common symptoms of a water heater blowing cold air include the water not getting hot enough, the water temperature fluctuating, or the heater running constantly without the water getting hot. If your water heater is blowing cold air, it's important to address the issue promptly to prevent further damage and ensure you have reliable hot water in your home.