How much does it cost to run an electric tankless water heater?
An electric tankless water heater heats water on-demand as it flows through the unit, eliminating the energy waste of keeping a large tank hot around the clock. Because these units draw substantial electrical power during operation—firing up heating elements only when someone turns on a tap—their cost profile depends heavily on how often hot water is actually needed and the efficiency of the heating pathway itself.
Electric Tankless Water Heater running cost calculator
- Per day
- $1.87
- Per month
- $56.88
- Per year
- $682.55
- CO₂ / year
- 1606 kg
Based on 4015 kWh per year. Adjust the price per kWh to match your latest electricity bill for an exact figure.
At 5500 watts used 2 hours a day, an electric tankless water heater costs about $1.87 per day, $56.88 per month and $682.55 per year on an average rate of 17¢ per kWh — roughly 4015 kWh and 1606 kg of CO₂ over a year. Enter your own electricity rate and usage in the calculator above for a figure matched to your bill.
The most misunderstood aspect of tankless water heater costs is that they don't use energy when idle. Unlike tank models that quietly bleed heat through their insulation day and night, a tankless unit consumes power only during the minutes when water is flowing through the heating chamber. However, because they must heat water rapidly to useful temperatures, they demand a very high electrical draw while active—often requiring dedicated, heavy-gauge wiring and sometimes even a 240-volt circuit upgrade. Homeowners should understand that the actual operating cost depends more on daily hot-water consumption patterns than on the heater's mere existence in the home.
Water temperature and flow rate are the primary drivers of energy consumption once a tankless unit is installed. A unit set to deliver 120°F water to an already-warm pipe will work less hard than one fighting to raise frigid groundwater to 130°F in winter. Similarly, turning on a shower uses more energy than filling a small sink because the volume and time are greater. The efficiency rating on a tankless heater—typically shown as a percentage rather than gallons-per-minute—reflects how much of the electrical input actually reaches the water versus being lost through the unit's body or venting. Higher efficiency ratings (above 95 percent for electric models) mean less waste, though even mid-range units are usually quite efficient since there's no standing tank to lose heat through.
Sizing is critical and often done incorrectly, leading to false economy assumptions. A household that buys an undersized tankless heater to save upfront money may find that simultaneous showers or dishwasher use during a shower causes the temperature to drop or flow to reduce—forcing family members to adjust usage or run the unit longer than necessary. Conversely, an oversized unit will cycle on and off inefficiently for small draws. The correct approach is to calculate peak simultaneous hot-water demand: simultaneous showers count fully, but a single shower running while the dishwasher heats its own water does not. Installers who ignore this often leave customers frustrated and blaming the heater rather than the installation choice.
One frequently overlooked cost factor is the electricity demand charge some utilities impose, separate from consumption. If your utility has demand-based pricing, running a 5500-watt unit can spike your monthly demand fee even if the unit runs only briefly. This makes tankless systems less economical in areas with steep demand charges and more attractive where consumption-only pricing applies. It's worth asking your utility directly or reviewing an older bill before committing to a tankless system in a region you're unfamiliar with.
Maintenance affects long-term cost efficiency more than many owners realize. Hard-water deposits accumulate inside the heating chamber, insulating the elements and forcing them to work harder and longer to reach target temperature. Annual or semi-annual descaling with a mild acid solution—a straightforward process using a small pump kit—can maintain efficiency and lifespan. Neglecting this maintenance can gradually degrade the cost profile, turning a theoretically efficient unit into an energy-hungry one over five to ten years.
Frequently asked questions
- Do tankless water heaters really save money compared to a traditional tank?
- That depends on your household's hot-water use and local electricity rates. Tankless heaters eliminate standby losses, so they're cheaper to operate if you use less than 40 to 50 gallons of hot water per day, which is typical for smaller households. Larger families or heavy users may see less dramatic savings because the tankless unit works at high power when in use. The figures above compare this specific unit to typical tank models—check whether your usage pattern matches.
- Why does my tankless water heater seem to use more power than expected?
- Tankless units consume high power only while actively heating water. If your usage has increased, or if you've adjusted the setpoint temperature higher, runtime increases proportionally. Hard-water scaling inside the heating chamber also forces elements to work longer; if you haven't descaled recently, that could explain higher consumption. Finally, if the unit is simultaneously supplying multiple hot-water outlets, its heating elements are working at full capacity—this is expected and necessary.
- Can I install an electric tankless heater myself, or do I need an electrician?
- Electric tankless heaters almost always require an electrician. The electrical demands are substantial and typically require upgrading your home's service panel, running new wiring, and installing a dedicated breaker—often 40 to 60 amps at 240 volts. DIY installation risks both safety hazards and voiding the warranty. Budget for professional installation when calculating total cost to own.
- How often should I descale an electric tankless water heater?
- In soft-water areas, annual descaling is sufficient. In hard-water regions, every 6 months may be needed to prevent efficiency loss and maintain warranty coverage. Many manufacturers require documented descaling as a warranty condition. You can do it yourself with an inexpensive pump kit and a gallon of white vinegar or a descaling solution. Skipping this maintenance gradually raises operating cost and shortens the unit's lifespan.
- Does running the dishwasher while someone showers impact the cost?
- Yes, in two ways. First, if the dishwasher heats its own water using the tankless heater, the unit works harder and longer to supply both applications simultaneously, increasing energy consumption during that period. Second, simultaneous loads may reduce water pressure or temperature at the shower, prompting longer showers to compensate. To minimize cost, space out major hot-water activities—shower first, then run the dishwasher—so the heater isn't overtaxed.
- What efficiency rating should I look for when comparing electric tankless models?
- Electric tankless heaters are inherently more efficient than gas models—most exceed 95 percent efficiency. The variance between units is smaller than you might think, so focus instead on whether the unit fits your household's peak demand (gallons per minute at desired temperature), its warranty length, and its warranty coverage for descaling maintenance. A slightly less efficient unit that's properly sized and maintained will cost less to operate than an oversized, neglected unit.