The answer to 'water heater blowing cold air' is that the most common cause is a malfunctioning heating element or thermostat. This can happen due to age, mineral buildup, or a problem with the electrical components. Symptoms include inconsistent or no hot water, and the water heater making strange noises.
In many cases, this issue can be fixed by a homeowner through simple troubleshooting and replacement of the faulty part. However, if you are not comfortable working with electrical components or are unsure of the root cause, it's best to call a professional HVAC technician to diagnose and repair the problem. They can safely inspect the water heater, test the electrical system, and replace any broken parts to restore hot water function.