DIY: Flush Your Water Heater and Check/Replace Your Anode

I’m not proud to admit that this DIY project is something I put off for way too long, and I feel stupid because it’s one of the easiest things you can do to save money every month, while prolonging the life of your gas or electric water heater: flushing the tank and inspecting (and replacing, as needed) your sacrificial anode.

“What’s an anode,” you ask? Don’t feel bad, I didn’t know either. And I promise I’ll get there… but first, let me explain what caused me to start looking at my water heaters in the first place: icky rust-colored water.

Rust Against the Machine

Rust in your hot water is a common occurrence. Nearly all hot water tanks are made out of steel, and everyone knows that if you allow water to stay in contact with steel long enough, steel will rust. Most water heaters are coated on the inside with a layer of porcelain enamel to help slow down the corrosion, but even that interior lining will eventually wear down and allow the steel to corrode. As the steel corrodes, it flakes off and settles at the bottom of your hot water tank, and then eventually breaks down further into fine particles of rusty sediment.

The above cutaway diagram shows the basic parts of a standard gas water heater. If you have an electric water heater (like we have at our cabin because there’s no natural gas out there), it’s very similar, except instead of a gas burner and burner control valve, you’ll have an electric element near the bottom and no exhaust flue on top.

The first problem with sediment on the bottom of your hot water tank is that it will act as an insulating barrier between the flame and the water, meaning you’ll burn way more gas (and spend way more money) every day to heat the water in your tank. The thicker the sediment layer, the less efficient the tank.

However, most people never realize they’ve got a thick layer of rusty sediment sitting at the bottom of their water heater until it builds up high enough to touch, or get close to touching, the end of the dip tube (shown in blue in the above image) where cold water comes into the tank and sends rusty particulate swirling around the tank, where it gets sucked into the hot water tube at the top of the tank (shown in red above), which causes rusty water to come out of your faucet or shower head. Eww.

If that happens, or if you want to prevent it from happening, you need to flush your water heater.

Flush it Out, Push it Out, Waaaaay Out!

As a preventative maintenance step, you should flush your water heater at least once a year, or even every six months. Don’t worry, it’s easy. So easy, you’ll kick yourself for not doing it sooner.

Turn the gas burner knob on your water heater all the way down to the “Vacation” setting. This will prevent the burner from coming on while you drain the tank.
Turn off the cold water shutoff valve that feeds water into your tank. You don’t need to shut off your house’s main water valve.
Connect a standard hose to the drain valve at the bottom of your hot water tank. You can use your garden hose, but I recommend buying a shorter hose from a home improvement store just for this purpose, and then storing it in the same room as the water tank. You’ll need the far end of the hose to be at a lower elevation than the drain valve. If you have a drain in the floor of the room where your hot water tank lives, that’s the ideal spot to put the hose. I generally remove the drain cover and shove the hose down into the drain.
If you have a recirculating pump for your hot water line, turn it off, and close the valve that feeds back into the water tank. If you don’t have one, skip this step.
Slowly open the drain valve until it’s all the way open. Be careful, the water inside the tank is hot. You should hear water draining from the tank and down the drain, or outside, or into the bathtub, or wherever else you put the other end of the hose. Warning: you may be shocked at how much gunk was in the bottom of your water heater. But take comfort in knowing you’re fixing it now, and will never let it get that bad again. 🙂
Turn on (all the way) the hot water tap at a sink that’s closest to your tank and leave it open. This prevents a vacuum from forming and allows the tank to drain more quickly and fully. Water should stop coming out of the faucet within a minute, but keep the tap open.
Once the tank is mostly drained (you can tell when the drain hose has just a trickle of water), turn the cold water valve back on while leaving the drain valve open. You’ll see (or hear) water coming out the drain hose again. Let it flush for a minute or two, then close the drain valve.
Let the cold water refill your tank for a couple of minutes, then shut off the cold water valve again and open the drain tube. Repeat steps 7 and 8 a few times, filling and draining, until the water coming out of your drain hose is clear.
After at least 3-4 flushing cycles, close the drain valve, remove the hose, and make sure your cold water valve at the top of the tank is open, allowing the tank to fill completely.
Turn the temperature setting on your gas valve back to your normal setting, and re-enable your recirculating pump and valve (if you have one).
When the hot water faucet you opened in step 6 starts flowing normally again, you can turn it off. You should also go to every hot water fixture in the house and turn them on for a few seconds to allow all the air in the hot water lines to blow out.
You’re flushed!

You Thought I Forgot The Anode

I promise, I didn’t! We already discussed the fact that most hot water tanks are made out of steel, and that the basic chemical formula of steel plus water equals rust. So, in many water heaters, a long metal stick made of aluminum, or magnesium, or zinc, or some combination of those metals, is inserted from the top of the water heater down into the tank. That rod is a sacrificial anode, and it works using a chemical reaction called electrolysis, allowing the anode to corrode (on purpose) instead of the steel inside the tank. Electrolysis occurs any time two different types of metals are touching under water: the least “noble” metal (meaning the more reactive one) will always corrode before the more noble metal will. And because aluminum, magnesium, and zinc are all less noble than steel, they make great anodes.

Anode rods are relatively cheap. I buy them for around $25 online or at plumbing supply stores, which is way cheaper than prematurely replacing your water heater. They’re designed to be replaced on a regular basis. Exactly how regular depends on a number of factors: how hard your water is, how often you use hot water, whether you use a water softener, the quality of your tank’s internal lining, and a number of other factors.

From time to time, you should inspect your anode to see how corroded it is, and whether or not it needs to be replaced. A great time to remove your anode for inspection is while you’re flushing your water heater. Make sure the cold water valve is turned off, and that at least some of the water is drained from your tank so that water doesn’t spill out the top of your tank when the anode is removed.

There are two types of anode rod designs: standalone anodes and anodes that are integrated with your tank’s hot water tube. Both require slightly different procedures to remove, inspect, and replace.

A standalone anode has a 1 1/16″ (that’s one and one-sixteenth inch) hexagonal head on top and a threaded collar underneath. Here’s what a new one looks like, next to one that’s corroded to the point that it needs replacement:

New Anode and Corroded Anode

If you have a standalone anode in your hot water tank (like we do at our Seattle house), you should be able to see the hexagonal head on top of the tank (unless it’s under some sort of access cover). With the tank partially drained and the cold water valve turned off, use a 1 1/16″ socket to loosen the anode.

Fair warning: if your hot water tank is a few years old, and you’ve never removed the anode, it’s probably rusted in tight and will be WAY harder to remove than it sounds. The manufacture date shown on the side of my water heater was 1996, and I didn’t even realize my water heater had an anode until 2012, so I had to go to extreme measures to remove mine, like spraying it with anti-seize bolt loosener (available at most auto parts stores) and asking my 300lb Icelandic power-lifter and black belt karate buddy Axel Adalsteinsson to supply the muscle with a cheater bar. You might also consider using an impact wrench if you don’t have an Icelandic buddy handy.

If you can’t find an anode on top of your hot water tank, you may have an anode that’s integrated with the tube that pulls hot water from your tank. The hot water tanks at our Utah vacation house have integrated anodes, and here’s what they looked like when I last removed them:

Integrated anode connected to hot water outlet

To remove an integrated anode from your tank, it’s best to have two pairs of channel-lock pliers or plumber’s wrenches. With the tank partially drained and the cold water valve off, use one wrench to hold the anode in place while you loosen the hot water line with the other wrench. Once the hot water line is removed (have a towel handy, it will drain a bit), gently grip the non-threaded portion of the exposed collar and turn counter-clockwise to loosen where the anode is threaded into the tank.

With either type of anode, once you’ve got it free, pull it up out of the tank and and inspect it. If it’s heavily corroded (as shown in both examples above), pull it all the way out. If you can see any part of the steel wire core on your anode, it needs to be replaced. If it’s just slightly chewed up, then you’re fine to keep it in there, and check it again in six months (set a reminder in your phone or calendar).

If it needs to be replaced, take the old anode with you to a plumbing supply or hardware store so you can get the right size replacement, or measure it and order one online. A few inches shorter or longer than the original isn’t a big deal, and if you can only buy one that’s too long to fit in your tank, a hacksaw can solve that problem fairly quickly. I keep a spare anode next to each water heater, so that when I inspect the old one and discover it’s time to replace it, I can install the spare right away, then purchase a new spare later.

When installing an anode, I recommend using plumber’s teflon tape to help ensure a tight seal, prevent rust, and make removing for inspection every six months far easier.

The Metal! (Yes, I’m a Tenacious D fan)

What type of metal you should choose for your anode depends on the water in your area.

In most cases, the magnesium anode rods are preferable over the aluminum ones, as they will last longer than aluminum ones. In general, the magnesium rods will have a small “bump” on the top, while the aluminum ones have a flat top.
If you have extremely hard water, aluminum anode rods are often your best choice. Magnesium anode will only last 1 or 2 years against really hard water.
So called “zinc” anode rods are actually just aluminum rods with about 10% zinc mixed, which helps fight sulfur smells in your hot water. They’re slightly more expensive than magnesium or aluminum rods, but are worth the upgrade come replacement time if your hot water smells like rotten eggs.

You can experiment with the different types over a few years to see which metal work best for you.

Congratulations… You’re a Plumber!

OK, so maybe you’re not quite ready to hang out with Mario and Luigi professionally just yet, but just knowing that your water heater has a user-replaceable anode is more than most people. Regular flushes of your hot water tank and inspection/replacement of your anode can extend the life of your water heater by years… if not decades, and save significant money every month by lowering the amount of energy required to heat the water in your tank.

So instead of waiting (like I did) until you actually see rust in your water, be proactive with a 6-month schedule of flushing your tanks and inspecting your anodes. I also recommend attaching a written log to your water tank, or use an online Google spreadsheet, to track how often you flush and inspect/replace the anode. Happy flushing!

Oh, and if you ever need a 300lb Icelandic power-lifter black belt to remove a rusted anode, sing a Viking ballad, or scare the women and children in your village, I know one that makes house calls.