Gas tankless water heaters deliver 2–3x more hot water flow than electric models and dominate whole-home applications in cold climates. Electric tankless heaters cost 40–60% less to install, require zero venting, and reach near-perfect 0.99 UEF efficiency. The right choice depends on your climate, hot water demand, available infrastructure, and budget.
Here is every metric compared, with real numbers from 2026 product data.
The Complete Head-to-Head
Efficiency: Electric Wins on Paper
Electric tankless heaters convert 96–99% of input energy into hot water. Gas condensing units convert 90–97%. Gas non-condensing converts 80–85%. On a pure efficiency basis, electric wins.
But efficiency is not the full picture. The relevant question is: how much does each BTU of delivered hot water cost?
Cost Per Gallon of Hot Water
Using a 60F temperature rise (moderate climate):
Key finding: Natural gas tankless costs $0.013–$0.016 per gallon of hot water. Electric tankless costs $0.017–$0.046 per gallon. Gas is cheaper to operate everywhere except areas with very cheap electricity (under $0.10/kWh) or very expensive gas (above $2.00/therm).
Propane tankless costs $0.033 per gallon — roughly equal to electric at $0.19/kWh. If your propane costs above $3.00/gallon, electric may be cheaper to operate.
The crossover point: Electric tankless operating costs equal gas tankless when your electricity rate divided by your gas rate per therm equals approximately 0.078. At $1.20/therm gas, the electric breakeven is $0.094/kWh. Below that electricity rate, electric is cheaper. Above it, gas is cheaper.
Flow Rate: Gas Wins Decisively
This is where gas pulls far ahead. The physics cannot be argued:
A 199,900 BTU/h gas burner delivers usable heat of roughly 186,000 BTU/h after efficiency losses (at 0.93 UEF). Converting to kW: that is approximately 54.5 kW of usable heating power.
A 36 kW electric unit delivers about 35.6 kW of usable heat (at 0.99 UEF).
Gas delivers 53% more heating power. At a 77F temperature rise (typical northern U.S. winter), that translates to:
- Gas condensing: 4.5–5.4 GPM (two full showers plus fixtures)
- Electric (36 kW): 2.2–2.7 GPM (one shower, maybe a faucet)
For a family of 4 or more, or any home needing simultaneous multi-fixture hot water in a cold climate, gas is the only practical single-unit solution.
Installation: Electric Wins on Simplicity
Electric tankless installation is fundamentally simpler:
What gas requires that electric does not: Gas supply line (3/4 inch minimum, possibly a new run from the meter), venting pipes through a wall or roof (PVC or stainless steel), condensate drain (for condensing units), combustion air supply, and carbon monoxide testing.
What electric requires that gas does not: Dedicated 240V circuits (2–4 of them), heavy-gauge copper wire from the panel, sufficient panel capacity (possibly a panel upgrade), and double-pole breakers.
Installation time: Gas takes 4–8 hours. Electric takes 2–4 hours (without panel upgrade).
Who installs: Gas requires a licensed plumber with gas certification. Electric requires a licensed electrician (for wiring) and can sometimes be done by a qualified plumber for the water connections.
Installation Cost Comparison
Without a panel upgrade, electric wins by $1,500–$2,500 on total installed cost. With a panel upgrade, the gap narrows to $500–$1,000.
Climate: The Decision-Maker
Climate determines which fuel type is practical for whole-home applications. This is not a preference — it is physics.
The 55F groundwater line: If your winter groundwater temperature is below 55F, a single electric tankless unit cannot reliably serve more than one fixture at a time. Above 55F, a 36 kW electric unit can handle 2 fixtures. This makes 55F groundwater the practical dividing line between electric-viable and gas-required for whole-home applications.
Environmental Impact
At Point of Use
Electric tankless produces zero emissions at the point of use. Gas tankless combustion produces CO2, water vapor, and trace NOx.
A gas condensing unit burning natural gas emits approximately 117 lbs of CO2 per million BTU. For a typical household (250 therms/year), that is about 2,925 lbs of CO2 annually from water heating alone.
Including Grid Emissions
Electric heaters are only as clean as the grid that powers them. The national average grid emission rate is about 0.86 lbs CO2/kWh. For a household using 3,700 kWh/year on electric tankless, that is 3,182 lbs of CO2 — slightly more than gas.
However, grid emissions vary dramatically by state. In Washington (hydro-dominated), grid emissions are 0.08 lbs/kWh, making electric nearly carbon-free. In West Virginia (coal-dominated), grid emissions are 1.8 lbs/kWh, making gas the cleaner option.
If you have solar panels, electric tankless powered by your own solar is the cleanest option, period.
Safety Comparison
Electric is objectively safer because it eliminates combustion-related risks entirely. Gas units are safe when properly installed and maintained, but the consequences of improper venting (carbon monoxide) are severe.
Real-World Decision Scenarios
Scenario 1: New Home in Houston, TX
Groundwater: 68F. Peak demand: 4.5 GPM. Gas available? Yes.
Electric option: EcoSmart ECO 27 ($480 unit). Delivers 4.6 GPM at 52F rise. Total installed: $1,650. Annual cost: $310 at $0.135/kWh.
Gas option: Rinnai RU160iN ($1,500 unit). Delivers 6.5 GPM at 52F rise. Total installed: $3,400. Annual cost: $215 at $1.10/therm.
Winner: Electric — $1,750 cheaper to install, only $95/year more to operate. Payback on gas premium: 18+ years. Electric is the clear choice.
Scenario 2: Existing Home in Boston, MA
Groundwater: 45F. Peak demand: 6.0 GPM. Gas available? Yes.
Electric option: EcoSmart ECO 36 ($650 unit). Delivers 2.8 GPM at 75F rise — barely one shower. Would need two units. Total installed (2 units): $4,200.
Gas option: Navien NPE-2 240S ($1,800 unit). Delivers 5.3 GPM at 75F rise — two showers. Total installed: $4,500.
Winner: Gas — virtually the same installed cost, but one unit instead of two, with far superior flow capacity. Gas is the obvious choice.
Scenario 3: Rural Cabin, No Gas Line
Groundwater: 50F. Peak demand: 2.5 GPM. Gas available? No (would need propane tank).
Electric option: EcoSmart ECO 24 ($430 unit). Delivers 2.0 GPM at 70F rise — tight but workable for a cabin. Total installed: $1,300.
Propane option: Rinnai RU160iP ($1,600 unit) plus 500-gallon propane tank ($800–$1,500). Total installed: $5,000–$6,000.
Winner: Electric — $3,700–$4,700 cheaper, adequate for cabin usage, no propane delivery hassles.
Scenario 4: Eco-Conscious Home with Solar Panels
Groundwater: 58F. Peak demand: 5.0 GPM. Solar array: 10 kW.
Electric option: EcoSmart ECO 36 ($650 unit). Solar offsets most water heating. Annual out-of-pocket electricity: ~$100. Total installed: $1,900.
Gas option: Navien NPE-2 180S ($1,500 unit). Annual gas: $250. Total installed: $3,800.
Winner: Electric — lower installed cost AND near-zero operating cost with solar. Payback vs gas: immediate.
Key Takeaways
- Choose gas if: Cold climate (groundwater below 55F), need 2+ simultaneous fixtures, gas line already available, prioritize capacity over cost
- Choose electric if: Warm climate (groundwater above 55F), single-fixture or light demand, no gas line, want simplest install, have solar panels, prioritize low upfront cost
- Gas costs more to install ($2,700–$6,000 vs $1,100–$3,400) but less to operate ($200–$400/year vs $365–$900/year)
- Electric is near-perfect efficiency (0.99 UEF) but limited by panel capacity and flow rate
- The 55F groundwater line separates electric-viable from gas-required for whole-home use
- Both qualify for IRA tax credits (gas condensing UEF 0.95+, all electric models)
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