Choosing between a gas and an electric tankless water heater hinges on operating costs, energy prices, and hot water usage patterns. This article breaks down how each type consumes energy, what drives the bill, and provides practical cost comparisons to help homeowners across the United States make an informed choice.
How Tankless Water Heaters Work
Tankless water heaters, also known as on‑demand heaters, heat water as it flows through the unit rather than storing hot water in a tank. Gas models typically use a gas burner to heat water, while electric models use electric coils or a high‑efficiency heating element. Because there is no standby heat loss associated with a storage tank, tankless units are generally more energy efficient on a per‑gallon basis. However, the capacity and flow rate (measured in gallons per minute, or GPM) determine whether the unit can supply hot water for simultaneous demands, such as a shower and a faucet at the same time. Efficiency ratings, installation requirements, and venting considerations influence total lifecycle costs in addition to the operating cost per unit of energy.
Factors Driving Operating Costs
Several variables shape the annual operating cost of a tankless water heater:
- Energy source and price. Natural gas tends to be cheaper per energy unit than electricity in many U.S. regions, but regional rate differences matter. Electricity prices vary by state and utility, while gas prices follow local market conditions and seasonal demand.
- Energy efficiency and energy factor (EF) or uniform energy factor (UEF). Gas and electric tankless models punish little standby loss, but the effective cost depends on how efficiently heat is transferred from the energy source to the water. Higher EF/UEF values generally translate to lower operating costs.
- Hot water demand and flow rate. The more hot water needed simultaneously (for example, multiple showers or appliances running at once), the larger the unit and the more energy consumed. On a gas system, higher input BTU ratings may be required to meet peak demand, influencing fuel use and cost per hour of operation.
- Temperature rise. The difference between incoming water temperature and the desired outlet temperature (temperature rise) directly affects energy usage. Colder incoming water or higher target temperatures increase energy per gallon.
- Installation and maintenance costs. While these aren’t “operating” costs, proper venting, sizing, and routine maintenance affect long‑term efficiency and reliability, which in turn influences ongoing energy use and bills.
Comparing Gas and Electric Costs
To compare operating costs, it helps to use a simple framework: annual energy use is a function of hot water volume, temperature rise, and energy efficiency. A practical estimate uses these steps:
- Estimate annual hot water usage in gallons (gal/year).
- Estimate a typical temperature rise (difference between incoming water and desired output, in °F).
- Convert to energy units (BTU or kWh) using the water heating formula: BTU = gallons × 8.34 × °F rise.
- Apply the energy source price and system efficiency to obtain annual cost.
Illustrative example with commonly cited inputs:
- Annual hot water usage: 60 gallons per day ≈ 21,900 gallons per year.
- Temperature rise: 70°F (typical for many homes).
- Gas model: efficiency around 0.80 (80%). Gas price: about $1.00 per therm (100,000 BTU).
- Electric model: efficiency around 0.95 (typical modern electric on‑demand). Electricity price: about $0.15 per kWh.
| Metric | Gas Tankless | Electric Tankless |
|---|---|---|
| Annual BTU needed (approx.) | 21,900 gal × 8.34 × 70 = ~12,785,000 BTU/yr | Same BTU need as heat source is the same for the water |
| Converted to Therms (gas) | 12,785,000 BTU ÷ 100,000 = ~128 therms/yr | N/A |
| Gas price estimate | $1.00 per therm → ~-$128/yr | N/A |
| Annual gas operating cost (rough estimate) | ≈ $128/yr (not including venting or maintenance) | N/A |
| Electrical energy equivalent (kWh) | N/A | 12,785,000 BTU ÷ 3,412 ≈ ~3,745 kWh/yr |
| Electric price estimate | N/A | $0.15 per kWh → ~-$562/yr |
| Annual electric operating cost (rough estimate) | N/A | ≈ $562/yr |
| Indicative cost comparison | Generally lower than electric for similar usage in regions with cheaper gas | Typically higher operating cost in electricity‑dominant regions, unless electricity is unusually cheap or unit is exceptionally efficient |
The table above uses conservative estimates to illustrate the scale of differences. Real‑world results vary by region, energy prices, and system design. In many U.S. markets, gas tankless setups offer noticeably lower annual operating costs, especially where natural gas remains affordable and reliable. Electric tankless systems may still appeal in areas with high gas prices, limited gas availability, or where electricity prices are competitively low and the system benefits from advanced electric heat pump technology.
Real-World Cost Scenarios
Consider two common scenarios to understand how operating costs can differ in practice:
- Regional price influence. A home in the Midwest with affordable natural gas might see gas tankless annual costs around the low hundreds of dollars, assuming typical hot water use. In the same region, an electric model could approach or exceed a couple of hundred dollars, depending on usage and electricity rates.
- High hot water demand. For households with frequent hot water use (large families, high simultaneous demand), electric tankless units may require larger, more expensive electric service upgrades and a larger heat output. While efficiency can be high, the higher kW draw during peak demand can raise electricity costs and potentially trigger demand charges in some locales.
Other practical considerations include cold‑weather performance for gas models, venting requirements, and the need for water filtration in some regions. Efficiency labels from Energy Star and manufacturer specifications help quantify expected operating costs, but real costs depend heavily on local energy prices and installation specifics.
Other Considerations and Practical Guidance
Beyond operating costs, several factors influence the long‑term value of gas vs electric tankless water heaters:
- Installation complexity. Gas tankless heaters require proper venting and may need gas line upgrades. Electric units typically require a substantial electrical circuit and can demand a high amperage service, especially for high‑flow models.
- Peak demand and sizing. Correctly sizing the unit to meet peak demand avoids overworking the system, which can minimize both energy use and maintenance needs.
- Maintenance costs. Gas units may require periodic vent inspection and combustion system maintenance. Electric units generally have fewer moving parts but still need periodic checks for mineral buildup, particularly in hard water areas.
- Environmental considerations. Gas combustion emits carbon dioxide and other pollutants, while electric heating is only as clean as the electricity grid. In regions with renewable‑heavy grids, electric tankless heaters can offer lower indirect emissions.
Takeaway for Homeowners
For most American homes, gas tankless water heaters tend to offer lower operating costs than electric tankless models, especially where natural gas prices are modest and hot water demand is steady but not extreme. Electric tankless systems can be attractive where gas is scarce, electricity is very affordable, or where homeowners aim to minimize combustion appliances. The best choice depends on local energy prices, installation feasibility, and desired hot water reliability. Consulting with a licensed plumber or licensed HVAC professional can help verify accurate sizing, cost projections, and installation requirements tailored to a specific home.
