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(NOTE:  Should you drain your water heater when you go on an extended vacation??  Maybe... or maybe not!! Click HERE for NH's comments on this issue!)

About 15 years ago, a customer asked me to remove an orphan hot water tank that had been in her basement for over 20 years. Some folks don't bother removing their old tanks from the basement... they just install a new one next to the old one. You know... over there in the corner next to the rusting '62 Chevy!

Because of the size of this cast iron tank... over 6 feet tall and at least 100 gallons... and the small doorway to the basement, I was forced to cut it into pieces. I think they built the house around that old water heater!

Anyway, I was astonished when I took the top off and found that the tank had over two feet of sediment in the bottom! The old well that had serviced this home for so many years sure brought up a lot of grit!

No, Virginia, it is not absolutely necessary to drain the gunk from the bottom of your tank every year!

However, if your water heater is a few years old or you just bought a new home, you should drain it now to see just how much sediment you have accumulated. The amount of sediment that you observe in the drained water will help you to determine your future flushing schedule.

What is the sediment, and why is it a problem?

The sediment is simply any solid material that is not dissolved in the water. This can be sand or other grit from a well, or any other stuff that has gotten into the municipal water mains. Many municipal water systems are not filtered so there is always a small amount of "stuff" moving through the pipes. This "stuff" settles to the bottom of the tank.

A dog's best friend...A humongous one-time blast of sediment can come into your home after the Water Company (applause, please) flushes out their lines. Have you ever hydroplaned a Yugo through a blast of water from a fire hydrant... with the "High Water" signs and life guard stand? This is how sediment is cleared from these main lines. If your house's plumbing connects to this main, the sediment lifted from this sudden burst of water can be enough to clog your toilet inlet valves, your faucet aerators, and deposit a goodly amount in your hot water tank. As a courtesy, most water companies try to give notice of flushing in your area, and advise residents not to run the water. If you don't heed their warning, you will grasp the deeper meaning of "hard" water!

Small accumulations of sediment are not a serious problem. However, as with the example of benign neglect mentioned in my prologue, the depth of the sediment can interfere with the functioning of the drain valve, increase the amount of dissolved minerals in the hot water, and even affect the efficiency of the lower heating element if allowed to accumulate.

Most people have at some time or another been told not to drink hot water from the tap, but are unaware of the reason why. In your hot water tank, the minerals, salts, etc. that have settled in the tank can dissolve into the water. As you know, hot water can dissolve substances that will not dissolve in cold water, and in greater quantities. Plus, the chlorine in the water has an effect on the sediment, and may produce unwanted and possibly unhealthy chemical compounds. All the more reason to keep the sediment level in the tank low.

Clearing sediment from the hot water tank:

Note from NH:  Replacing the stock drain valve can dramatically increase your water heater's draining efficiency.  Curious?  Read more here.

1) Do whichever applies for your water heater... gas or electric:

  • Turn off the electricity to the water heater.  This is vital.  If an electric heating element turns on while not submersed in water, it will burn out, possibly leading to replacement of the entire water heater! 
  • If you have a gas hot water heater, you may be able to do this procedure with the gas on, but turned to the lowest setting. However, you must not let the tank drain more than 3/4 empty. This is easier to gauge if you use a bucket to measure the amount of water you drain. For your first ever flushing of your tank, though, I would recommend a full flush, which requires you to turn the gas to "pilot". You can do "touchups" later by draining a portion of the tank down, rather than a full drain.

2) Turn off the COLD water supply to the tank.

3) Attach a garden hose to the drain valve at the bottom of the tank.  Run the hose to a convenient drain location.  Be careful if you use a real cheapy garden hose... some of these become very soft when hot water runs through them, and may leak!  If you don't have a drain in the basement floor or suitable sump hole, you have my sympathies... this drain-down can take a while with a bucket! Oh... and be careful if you use a soft plastic bucket. It can also soften from the heated water so don't overfill it or burn yourself!

4) Open up the hot water side of any faucet. Open up the drain valve on the tank and allow it to empty. Miller time. That is, unless you don't have a sump...

NOTE: If the drain valve clogs, turn on the cold water supply to the tank to use water pressure to "blast" through the clog.

5) When the tank is empty, shut off the drain valve and turn on the cold water.  This will loosen up more sediment in the tank through the churning action of the cold water in the tank.  Let the tank fill partially and drain it again. In fact, if you find that the sediment starts to clog the drain valve, turn on the cold water supply to the tank, which will help loosen the sediment and blast it out.

If you have extreme amounts of sediment, you may have to repeat this procedure a few more times.  Look at the drain water... if it is running clear, you are done. Shut off the drain valve, open the cold water supply and allow the tank to fill. Once water comes out of the hot water faucet, the tank is full and your task is done!  Now, you can turn the electricity or gas back on to heat the water.

How frequently should you drain the sediment from your tank?

This depends on the source and purity of your water supply. Some pros recommend doing it annually, some every few years. I would recommend doing a partial drain down annually if you find any sediment in the tank, otherwise every couple of years.

Remember that with an electric water heater, you must turn the power off! Even a partial drain down may expose the upper heating element to the air and permanently damage it!

Is there any way to keep this sediment from accumulating in the tank?

Installing a whole house filtration system can make a real dent, especially if you have gritty well water!  They are fairly easy to install for someone with good plumbing skills, and not only help to reduce the sediment accumulation but prolong the life of all your plumbing fixtures and appliances.

Of course, depending on the ferocity of your filtration system some dissolved minerals may still eventually accumulate in the tank but hopefully in less significant amounts.

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