Understanding the Efficiency Gap
Standard electric resistance water heaters (Energy Factor approximately 0.95) convert 95% of electricity to hot water heat. Standard gas water heaters (Energy Factor approximately 0.60–0.67) lose significant heat up the flue exhaust. On raw efficiency alone, electric wins. But electricity costs more per BTU than gas in most U.S. markets — which is why gas water heating has historically been cheaper to operate despite lower efficiency. The comparison is fundamentally about fuel cost, not efficiency: at what electricity rate does electric water heating become cost-competitive with gas?
The Breakeven Electricity Rate
A typical household uses 4,000 kWh-equivalent of hot water annually. A 0.64 EF gas water heater uses about 250 therms/year at $1.40/therm = $350/year. A 0.95 EF electric resistance heater uses about 4,210 kWh/year at 18¢/kWh = $758/year. Gas wins at these national averages. The breakeven point: gas at $1.40/therm equals $0.041/kBTU; electric resistance becomes competitive at approximately 8–9¢/kWh — below national average but typical in Idaho, Washington, Oregon, and Louisiana. Residents in those states may find electric actually cheaper to operate.
Heat Pump Water Heaters: The Game Changer
Heat pump water heaters fundamentally change this comparison. At COP 3.5, a HPWH uses 1,200 kWh/year instead of 4,200 kWh/year for electric resistance — or instead of 250 therms for gas. At 18¢/kWh: HPWH costs $216/year vs. gas at $350/year. The HPWH wins by $134/year — and even though the federal tax credit for HPWHs (up to $300, 30% of cost) expired December 31, 2025, the equipment cost premium over a standard electric heater still typically pays back in 3–4 years from operating savings alone. At California rates (28¢/kWh), HPWH costs $336/year — still competitive with gas and dramatically cheaper than electric resistance at $1,179/year.
Installation Considerations
Gas water heater replacement requires gas line, proper flue venting, and expansion tank in closed systems — installation runs $300–$600 on top of equipment. Electric requires a 240V/30A circuit. Heat pump water heaters need 700+ cubic feet of unconditioned or semi-conditioned air surrounding them (they extract heat from the air), and they exhaust cool, dry air — a benefit in warm climates and seasons, a slight heating penalty in winter in heated basements. They also make noise similar to a window AC unit at about 50 dB. Basement, garage, or utility room installation is typical and practical for most homes.
Quick Reference: All Four Options at This Calculator's Default Inputs
For a household using 50 gallons of hot water per day (this calculator's default, on the lower end of the 50–80 gal/day range commonly cited for a family of 3–4) at national-average rates (18¢/kWh electricity, $1.70/therm gas), here's how the four main water heating options stack up before you plug in your own numbers above:
| System | Efficiency | Annual Operating Cost | Typical Install Cost |
|---|---|---|---|
| Heat Pump Water Heater | COP 2.5 | ~$193/year | $1,200+ |
| Gas Tankless | 84% (EF 0.84) | ~$185/year | $1,200+ |
| Gas Tank | 67% (EF 0.67) | ~$232/year | $800+ |
| Electric Resistance Tank | 95% (EF 0.95) | ~$507/year | $700+ |
At national-average rates, heat pump and gas tankless are nearly tied on operating cost, both meaningfully cheaper than a gas tank, and standard electric resistance is by far the most expensive to run despite being the cheapest to install. The gap moves with your local rates: heat pump water heaters pull further ahead as electricity gets cheaper relative to gas, while gas options pull ahead in regions with low gas prices and high electricity prices. Use the calculator above with your own local rates to see exactly where you land.