Every water heater slowly fills with sediment. Calcium and rust settle out of the water and collect on the bottom of the tank, and on a gas heater they sit directly between the burner and the water it is trying to heat.
The result is a heater that costs more to run, recovers more slowly, sometimes rumbles or pops, and wears out years early. Flushing it is a job you can do yourself in an afternoon with a garden hose.
This walkthrough follows Word of Advice TV on a standard tank heater. Most of the elapsed time is waiting for it to drain; the hands-on part is maybe fifteen minutes.
This is for tank heaters, not tankless
If your unit is a wall-mounted box with no storage tank, this is the wrong procedure. Tankless heaters are descaled by circulating vinegar through them with a pump, not drained through a hose. See how to install a tankless water heater for what that unit looks like.
How often, honestly
Manufacturers say once a year. In practice a great many heaters run their entire life without ever being flushed, and plenty of thirty-year-old tanks are still going.
The realistic answer: if you are on hard water, annually is worth it. If you are on soft water, every couple of years is fine. If you have just moved into a house and do not know its history, do it once and see what comes out - that tells you how often you need to.
What you need
A garden hose, a flathead screwdriver, and somewhere for the water to go. A bucket is useful for catching a sample so you can see what you are dealing with. That is the whole list.
The safety points
Two things matter. The water is scalding - it comes out at tank temperature, typically 120 to 140°F. And never let the burner or elements fire on an empty tank, which is why the gas goes to pilot and the breaker goes off before anything drains.
Other jobs on the same trip
While you are working on the plumbing, fixing a leaky faucet and winterizing the sprinklers use much of the same kit.
