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Gas or Electric: How to Tell, and Why It Changes Everything

Almost every useful question about a water heater fault depends on this answer, and it takes ten seconds to establish.

Answer first

The two kinds of water heater share almost no failure modes. A gas heater has a burner, a flue and a pilot or igniter; an electric one has elements and thermostats behind access panels. Ten seconds of looking decides which conversation you are about to have.

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The ten-second test

Look at the top of the tank. A metal flue pipe rising from it into the ceiling means combustion, so gas or oil. No flue, and two small rectangular access panels on the side of the tank, means electric — those panels cover the heating elements.

A gas heater will also have a gas line running to a control valve near the floor, and usually a small window or opening where a pilot flame is visible.

What can fail on gas

The pilot, the thermocouple that proves the flame, the gas control valve, and the flue if it stops drafting. A gas heater can also work perfectly and still be unable to keep up if sediment has insulated the burner from the water above it.

What can fail on electric

The upper element, the lower element, either thermostat, and the high-limit cut-out. Nothing can blow out, and nothing needs to vent. In exchange, elements scale up and burn out, and a failed lower element gives the runs-out-fast symptom.

What it costs to run

DOE puts water heating at 14% to 18% of the average household's utility bill, which is why the choice between the two is worth more than the price difference on the day.

Source: US Department of Energy, Which Water Heater Is Right for You?.

How long each lasts

DOE gives 10 to 15 years for a storage tank of either kind, about 20 for a tankless unit, and 10 to 15 for a heat pump water heater. Age is worth knowing before paying for a repair — the date is usually encoded in the serial number on the label.

Know the fuel and the symptom? That is most of the call.Gas and electric heaters fail in almost entirely different ways, so saying which you have gets you to the right person faster. We route the call and never charge you for it. Water heaters are what we write about; the number goes further.

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