How much does it cost to run a water heater per month?

For a typical household drawing 64 gallons a day at a 70 °F rise, running cost is roughly $22/month on gas or $58/month on electric resistance at common rates, and about $15/month on a heat pump. Your figure depends on your draw, your unit’s UEF and your utility rate — enter them to get your own number.

Is gas or electric cheaper to run?

Usually gas, because a therm is cheap relative to the electricity a resistance element uses — often around 60% cheaper to run. The exception is a heat-pump electric unit, which can undercut gas because its efficiency (UEF ~3.5) is far above 1. Your local rates decide it.

Does turning down the water heater save money?

Yes. Lowering the setpoint reduces the temperature rise and cuts both heating energy and standby loss. The common guidance is 120 °F — hot enough for use, low enough to limit scald risk and waste. The scald and bacteria tradeoff is the manufacturer’s and a professional’s call.

How much electricity does a water heater use?

A resistance electric tank for a busy household often uses on the order of 4,000–4,500 kWh a year; a heat-pump model delivers the same hot water on roughly a third of that. The exact figure is annual_BTU ÷ 3412 ÷ UEF — enter your draw and UEF to compute it.

How much does it cost to run a water heater?

Operating cost is not a mystery and it is not a fixed number off a chart — it is delivered heat ÷ efficiency × your rate. Plug in your $/kWh or $/therm and your unit’s UEF and the annual figure falls out, fuel by fuel.

By Francesco Zinghinì

People ask “how much does a water heater cost to run” expecting a single dollar figure, but the answer is a short formula with three inputs that are all specific to you: how much hot water you draw, how efficient your unit is, and what your utility charges. Once you see the formula, you can compare fuels honestly and spot where the money actually goes.

The formula

Start with the physics: it takes 8.33 BTU to raise one gallon of water 1 °F. So the heat you deliver in a year is annual_BTU = daily_gallons × 365 × 8.33 × ΔT, where ΔT is your temperature rise (output minus inlet). Then divide by the fuel’s energy content and the unit’s efficiency:

Electric: annual_kWh = annual_BTU ÷ 3412 ÷ UEF, then × your $/kWh.
Gas: annual_therms = annual_BTU ÷ 100000 ÷ UEF, then × your $/therm.

UEF (Uniform Energy Factor) is on the EnergyGuide label — roughly 0.92 for an electric-resistance tank, 0.62 for a conventional gas tank, 0.90 for a gas tankless, and about 3.5 for a heat pump (yes, above 1 — it moves heat rather than making it).

Worked example: the same house on two fuels

Take 64 gallons a day and a 70 °F rise. The delivered heat is 64 × 365 × 8.33 × 70 ≈ 13,621,000 BTU/yr. On electric resistance (UEF 0.92, $0.16/kWh): 13,621,000 ÷ 3412 ÷ 0.92 ≈ 4,339 kWh × $0.16 ≈ $694/yr. On gas (UEF 0.62, $1.20/therm): 13,621,000 ÷ 100,000 ÷ 0.62 ≈ 219.7 therms × $1.20 ≈ $264/yr. Same hot water, but gas costs about 62% less to run at these rates — and that caveat matters, because your rates decide the winner. Try yours in the operating-cost calculator and compare fuels in the energy cost by fuel tool.

Where a heat pump changes the story

A heat-pump (hybrid) water heater has a UEF near 3.5, so it uses roughly a third of the electricity of a resistance tank. On the same draw, our $694 resistance figure drops to about $182/yr — a saving on the order of $500 a year. It needs warm ambient space and clearance to work well, but on running cost alone it is the electric champion. See the heat-pump savings tool.

The levers that move the bill most

Volume. Fewer or shorter showers and a low-flow head cut daily gallons directly — the single biggest lever.
Temperature rise. Every degree you drop the setpoint (within the safe 120 °F guidance) trims ΔT and therefore energy; a warmer inlet in summer does the same for free.
Efficiency. UEF is a multiplier on the whole bill — a heat pump versus resistance is a 3× swing.
Standby loss. A tank loses heat around the clock; a tankless and good tank insulation cut that. It is why the same UEF on paper can run differently in practice.

Standby loss: the cost you pay for nothing

The operating-cost formula captures the energy you put into hot water, but a storage tank also loses heat around the clock whether you draw a drop or not — the tank sits full of 120 °F water in a cooler room and radiates. That standby loss is why two units with the same on-paper efficiency can run differently, and it is baked into the UEF rating, which is measured over a realistic daily draw. It also explains three practical savings: a well-insulated tank (or an add-on blanket where the manufacturer permits it) loses less; a right-sized tank loses less than an oversized one holding gallons you never use; and a tankless loses essentially none because it stores nothing. If your household draws little hot water but keeps a big tank hot, standby is a large share of your bill — and no amount of shorter showers touches it, only a smaller tank, better insulation or a tankless does.

Vacations and swing seasons are worth a thought too. Leaving a tank fully hot while you are away a week is pure standby waste; many units have a “vacation” setting that holds a lower temperature. And because ΔT falls in summer as the inlet water warms, the same shower costs noticeably less in July than in January — your annual figure is an average of a cheap warm season and an expensive cold one. Run the operating-cost calculator at both your winter and summer inlet temperatures to see the swing, and remember the biggest structural lever remains efficiency: moving from resistance to a heat pump changes the whole equation, not just the margins.

Common mistakes

Do not compare fuels on price per unit alone — a kWh and a therm hold very different amounts of energy, which is exactly what the formula normalizes. Do not use a nameplate wattage as a running cost; a 4,500-watt element does not run 24/7, it cycles to replace the heat you draw and lose. And do not trust a generic “$400 a year” from an article — it was written for someone else’s rates and habits. Enter your own $/kWh and $/therm from a recent bill and your unit’s UEF, and the number is yours and stays correct no matter how prices move.