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I've seen a few posts on the internet that say that water heaters should be flushed every year and "I bet you never knew you should be doing this!" After searching around most of the articles that explain why this is the case also include that "by the way, our company can provide this service for you" - so I'm a little skeptical of the actual necessity. I found one article that stated that most water from municipal supplies is good enough that it won't cause sediment build-up and doesn't require flushing. I've also seen an article describing how flushing old tanks could actually cause leaks by removing excess build-up that had been keeping them plugged.

So who actually needs to be flushing their hot water heaters regularly? For my own situation we live in a major US city and have a 3yo gas-powered tank heater. I'd expect ours is in good shape currently but want to make sure we're maintaining it properly.

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  • "we live in a major US city" implies you're on city water, not well water, right?
    – FreeMan
    Sep 7, 2022 at 17:05
  • I can say that I've probably changed out 5 water heaters in my life. Of those 5, around 4 of them were because there was a significant drop in the volume of hot water available. I live in a place where there's a lot of Lime in the water, which builds up in the water heater and takes up all the space in the heater. No space = no hot water. If the person owning the water heater had flushed it out regularly it would've lasted another 10 years. If you leave it too long, the lime builds up too much and becomes too much of a hassle to flush. So either flush regularly, or flush never (then change it)
    – Tyler M
    Sep 7, 2022 at 17:13
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    Also, if your water heater has a leak that is only holding together because of some build-up, that leak is going to grow by itself whether you flush it or not. Water heaters are steel, and as soon as there's a knick (or hole) anywhere, it gives access to the steel under the paint and it'll begin to rust through until there's nothing left. So yeah, that article sounds like the Author was doing a bit of a stretch there.
    – Tyler M
    Sep 7, 2022 at 17:17
  • @FreeMan Yes, that's correct
    – David K
    Sep 7, 2022 at 17:29
  • Once a year is the recommendation, also can usually just drain 1/2 or gallon every so often. Once a month if you find a lot, once every three to six months if not that much. Draining a water heater requires turning off the power and making sure the tank is completely full(have a hot faucet open) before turning power back on.
    – crip659
    Sep 7, 2022 at 17:39

3 Answers 3

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All tank water heaters collect stuff in the bottom of the tank. It's may be sand, dirt, small pebbles, mineral deposits, rust, or whatever. But over time you get a layer of it there.

In electric water heaters this doesn't cause much trouble other than some loss in capacity as the "stuff" displaces water in the bottom. But in gas water heaters it can insulate the bottom of the tank and prevent efficient heating of the water.

When I've had a gas water heater, I flushed it and often got quite a bit of material out.

Is it a "need" thing? Probably not, you may lose some efficiency and some lifetime of the unit but probably nothing drastic.

Would I pay someone to come and flush it? No. It's quick and easy to do yourself.

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    to emphasize this answer, "it's quick and easy to do yourself." Just connect a garden hose and open it up, let it drain out. If it gets stopped up, put a shop-vac on it. if it's still stopped up, shove a screwdriver in the open drain and unplug the gunk manually... IDK, just youtube "how to flush a water heater" lol
    – Tyler M
    Sep 7, 2022 at 17:15
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The obvious first step is: do a flush and examine the product. If it's perfectly clear, then no need to flush (or flush as often).

Now, water heaters with an internal electric heating element or with a heat exchanger (hot water supplied externally as a loop in a forced-hot water system) are more prone to generating metal gunk as the heat exchanger ages. Modern gas-fired heaters, where the heat is transferred through the inner wall, are generally not in need of flushing. Again, always worth checking every now and then.

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Do I really need to flush my hot water heater?

It's a bit of a chicken-and-egg situation.

You don't know that you didn't need it flushed until you flush it.

One important sibling task of flushing it though is replacing the anode rod. This is a sacrificial rod which deteriorates to extend the life of your tank.

So at minimum the bottom of your tank will likely have remnants of the anode rod.

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