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Flushing a water heater takes between 15 and 60 minutes, not including the time it takes for the water in the tank to cool down. The exact time will depend on the size of the tank. For example, a typical 40- to 60-gallon tank may take around 15 minutes to empty fully, while a large tank that’s 80 gallons and above can take longer, usually 30 to 60 minutes.

If you don’t flush your water heater, sediment can build up, harden, and form a layer that insulates the heating element from the water, causing your water heater to work less efficiently. This may cause issues such as temperature loss or longer heating times. The sediments can also corrode the tank's inner lining, weakening it and increasing the likelihood of a leak. 

If your unit breaks down, a water heater replacement costs between $840 and $1,670.

The following are key signs that your water heater has sediment and therefore probably needs flushing:

• No hot water or water temperature fluctuates

• Rumbling, hissing, or popping noises coming from the tank

• Leaks near the drain valve

• Hot water coming out of your taps looks rusty, cloudy, or has a metallic smell or taste

• Higher gas or electricity bills