Hot water heaters use a variety of means to heat water before circulating it through the house to faucets, showers and other hot water devices. A slight amount of noise is common in many water tanks and means the tank is filling with water or pumping out hot water. If the tank makes unexpected noises such as whining, creaking, popping or rumbling, then it is probably experiencing problems. Most of these noises are caused by sediment, which can affect water heaters differently based on what water is being used and how it is being heated.
Gas vs. Electric Water Heater
Gas water heater tanks have a gas burner installed in the bottom. This heater raises the temperature of water in the tank above it until it is ready to be pumped out. Electric water heaters work in a similar fashion, but instead of using a separate burner, a heating element is placed in the tank and heats the water as an electric current is passed through it.
Water can contain trace minerals that have been combined with the water molecules themselves, allowing them to pass through water plants and into household piping. Water with a large amount of these trace minerals is called hard water, while water with a relatively low count is soft water. When hard water is exposed to rapid heating, the minerals can precipitate from the water and settle in the hot water tank. These minerals are mostly calcium carbonate, with a mixture of sulphates and other silicates, depending on the area. Location also governs how hard the water is, and thus how much sediment will be released into the tank. Sometimes small amounts of soil or sand may be present in the water, adding to the sediment problem.
As the sediment builds up at the bottom of the tank, it cements itself to the metal surface and becomes difficult to remove. In gas heaters, pockets of water become trapped underneath parts of the sediment, usually close to the burner. These pockets of water heat more quickly than the rest of the water, and soon explode out of the sediment as steam. This results in many of the popping and rumbling noises hot water tanks make.
A hot water tank can be drained by turning off the heater, shutting down the water supply, and attaching a hose to the drain valve. As long as the flow of water is permitted---usually a hot-water faucet is kept on to prevent the formation of a vacuum---it will drain out some of the loose sediment in the tank. This can cause clogs in the drain valve, however, and will not work to remove some of the more permanent sediment.
Electric Water Heater Noises
Electric water heaters experience similar problems, but tend to produce whining or hissing noises instead of pops and rumbles. Water scale, or the deposits created by hard water minerals, is usually more of a problem with electric water heaters, because the scale can collect on the element itself. Over time, the element can be ruined by this build-up of deposits.
Many experts recommend regular draining of the water tank to make sure sediment is cleared out, as often as once a month to ensure no corrosion develops. If hard water is a problem based on location, there are devices that can remove minerals from the water before it reaches the hot water tank.