Tank Water Heaters

DOE's federal test procedure for water heaters sorts household hot water use into four standard tiers, based on gallons used per day. Every new unit's yellow EnergyGuide label reports an estimated annual energy cost built on one of these tiers, along with its rated capacity in gallons.

That same label also carries a First Hour Rating: how much hot water the unit can deliver during one demanding hour, not just how many gallons the tank holds. Two 50-gallon tanks can post different ratings depending on burner or element size and recovery speed.

ENERGY STAR's buying guidance recommends starting from the gallon capacity of the unit being replaced, then sizing up if the household has grown or added a fixture that pulls hot water at the same time as everything else, such as a second shower or a soaking tub. A contractor can weigh in on whether that calls for a larger tank.

On heat pump water heaters, federal guidance notes that running in the most efficient mode slows recovery time and lowers the First Hour Rating. That matters in a household used to back-to-back showers, since most models include a faster electric-resistance mode for that reason.

Inside the tank, a glass, or porcelain enamel, lining separates the water from the steel shell, but that lining is never perfectly continuous. A magnesium anode rod protects the microscopic bare spots it leaves through cathodic protection: the magnesium corrodes in the water's place, sacrificing itself so the steel tank does not rust through.

Rheem/Ruud's technical service documentation calls for the anode rod to be pulled and inspected annually, and replaced once more than six inches of core wire is exposed at either end. Running a tank with the rod removed voids warranty coverage and shortens the tank's life.

Water chemistry affects how fast the rod wears. The same documentation notes that softened water raises the anode's current demand and shortens its service life, and that water high in sulfate content, combined with sulfate-reducing bacteria, can react with a magnesium anode to produce hydrogen sulfide gas, the rotten-egg smell some households notice in hot water.

Heating water makes it expand. In an older, open system, that extra volume has somewhere to go, back down the supply line toward the main. Add a check valve, pressure-reducing valve, or backflow preventer on the incoming line, increasingly common on both wells and municipal connections, and the system becomes closed: the expanded volume from each heating cycle has nowhere to go.

In a closed system, that trapped expansion shows up as a pressure spike at the water heater every heating cycle. A thermal expansion tank, a small tank with an air-charged bladder installed on the cold-water line between the water heater and the backflow-prevention device, absorbs that volume instead of the pressure landing on the tank and its fittings.

Manufacturer installation guidance calls for checking the system's static water pressure at the water heater's drain valve, then setting the expansion tank's air pre-charge to match it before installation. Sizing depends on both tank volume and system pressure: larger tanks and higher pressures call for more expansion capacity.

Every tank water heater has a temperature and pressure relief valve near the top of the tank, a two-in-one safety device that opens if tank pressure climbs too high, and separately if water temperature reaches an unsafe level. Manufacturer guidance is direct: a discharge can mean an unsafe condition exists, and the recommended response is to contact a licensed plumber immediately.

A valve that is weeping or dribbling is usually reacting to pressure, often thermal expansion, or to mineral buildup such as calcium on the valve seat that keeps it from closing fully. A valve discharging large volumes of water points to an actual over-temperature event. Manufacturer guidance calls for the valve to be inspected and tested at every service visit.

• No T&P valve installed, or a pressure-only relief valve substituted in its place
• A T&P valve installed away from the tank, such as in the hot outlet line, instead of directly on the tank itself
• A discharge line that has been shortened, capped, fitted with a shutoff valve, or otherwise restricted

Minerals suspended in incoming water settle to the bottom of a tank and, over time, harden into sediment. In a gas water heater, that layer sits between the burner and the water it is heating, so the unit works harder and can rumble as trapped water boils underneath it. In an electric unit, the same minerals scale onto the heating elements, reducing heat transfer.

Maine's Center for Disease Control recommends private well owners test for hardness, iron, and manganese every three to five years, alongside routine bacteria testing. Those are exactly the minerals common in bedrock wells across Kennebec and Cumberland counties, and what settle out inside a tank over time.

Manufacturer guidance calls for flushing a residential tank at least every six months, and notes that areas with hard water may need it more often, in some cases monthly, depending on water conditions and household use. Flushing will not remove every trace of sediment, but a routine schedule keeps it from clogging the drain valve or insulating the burner.

This is one of the more straightforward maintenance visits. Our tank water heater flush, priced at $149, drains and flushes the sediment and checks the T&P valve while the tank is apart.