Tankless Water Heater Electricity Use: Costs & Savings

Tankless water heaters don’t run constantly like traditional tanks. They heat water on demand, which changes how much electricity they use and how that translates to your bill.

Understanding the real electricity use and running costs helps you decide if a tankless electric water heater fits your home and budget.

Tankless Water Heater Electricity Use Explained

A tankless electric water heater typically draws between 14 kW and 18 kW when operating, but it never runs continuously at maximum power. Instead, it adjusts power based on how much hot water you use, making its electricity use variable rather than constant.

The peak rating, like 18 kW on some units, shows the maximum power the heater can require at once, not the steady consumption. Your actual kW usage depends on factors like the water flow rate, temperature difference between inlet and outlet water, and how long you run it.

For example, a standard shower uses about 2 gallons per minute (GPM) of hot water. If the heater raises the water temperature by 50°F, it consumes roughly 1.8 kWh per 10 minutes of use. That’s 0.18 kWh per minute, so a 10-minute shower uses about 1.8 kWh, costing around 31 cents at 17 cents per kWh.

Tankless water heaters avoid standby losses common to storage tanks because they only heat water on demand. When off, their electricity use is negligible—often less than a watt for electronics—so standby electricity is not a concern.

Monthly electricity cost for tankless water heaters varies with household hot water use but generally ranges from $15 to $50 at average U.S. electricity rates (about 13 to 20 cents per kWh). Higher hot water demand or colder inlet temperatures push costs toward the upper end.

Matching power to real demand

Rheem 18kW 240V Tankless Electric Water Heater

The Rheem 18kW tankless heater adjusts power output to your actual hot water use, preventing unnecessary electricity consumption during low flow.

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How Tankless Electric Heaters Compare to Other Water Heater Types

Electric tankless water heaters cost more to run monthly than heat pump water heaters but avoid the standby heat loss of storage tanks, making them more efficient than conventional electric storage models.

Storage tank electric water heaters keep gallons of hot water ready, burning electricity constantly to maintain temperature. That standby heat loss adds up: about 10% to 20% of the energy goes into keeping water hot, even when you’re not using it. A tankless unit heats water only on demand, so it uses electricity only when you turn on a tap.

The Uniform Energy Factor (UEF) rating measures efficiency. Electric tankless heaters typically have UEF ratings between 0.98 and 0.99, meaning almost all the electricity goes directly into heating water when running. By contrast, electric storage tanks usually fall between 0.88 and 0.92 UEF because of standby losses.

Electric tankless heaters demand a high electrical load, often 14 to 18 kW at peak. That usually requires upgrading your home’s electrical panel and dedicated circuits, which means higher installation costs and complexity. Storage tanks run at lower wattage but run longer, while gas tankless heaters mostly use gas for heat and only a small amount of electricity for controls, saving on electric demand.

Fuel cost and availability also shape running expenses. Natural gas or propane for gas tankless heaters generally costs less per BTU than electricity, making those units cheaper to operate where gas is available. But if you live off-grid or in a place with expensive or unreliable gas service, electric models may be your only or best option.

Heat pump water heaters stand out as an efficient electric alternative. They use electricity to move heat from the air into the water rather than generating heat directly, so their UEF can be double or triple that of electric resistance units. Your electricity bill for a heat pump water heater will be lower, but the unit works best in warmer spaces with good ventilation.

The monthly cost for an electric tankless water heater depends on how much hot water you use and your local electricity rates. For example, a typical household might spend $30 to $50 per month on electric tankless water heating at 17 cents per kWh, while a heat pump water heater with the same hot water usage might cost $15 to $25 due to higher efficiency.

Installation costs for electric tankless units can run from $1,200 to $2,500 or more because of electrical upgrades required. Storage tanks usually cost less to install, around $800 to $1,500, since they need only standard wiring. Gas tankless units have higher installation costs related to venting and gas line work, often $2,000 to $3,500.

Choosing between these options means balancing upfront installation costs, fuel availability, running costs, and your hot water needs. An electric tankless heater offers endless hot water without standby loss but at a premium for electricity and installation. Heat pump water heaters cut electricity bills significantly but need space and climate that suits their operation.

If you want to know the price specifics for installing electric tankless heaters, see our detailed guide on tankless water heater installation cost.

Tools and Efficient Models to Manage Costs

Energy meters, timers, and top-rated tankless electric heaters

Power modulates to demand

Rheem 18kW Tankless Electric Water Heater

This Rheem model adjusts its power output to match your hot water use, which helps keep electricity use close to what you actually need. Its durable copper elements and precise digital thermostat let you control temperature to avoid overheating water and wasting energy.

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High efficiency with safety fe

Orbek 14kW Tankless Electric Water Heater

Orbek’s 14kW heater uses water-electricity separation to minimize scale buildup, maintaining efficiency and lowering electricity use. Its built-in chip adjusts heating power 20,000 times per second to keep temperature stable, which avoids energy spikes during use.

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Compact, efficient, and safe

SIVUATEK 14kW Tankless Electric Water Heater

This SIVUATEK unit eliminates standby energy loss with no preheating or idle power use, cutting your electricity costs by up to half compared to traditional heaters. It keeps water temperature stable despite pressure changes, and has advanced safety features to prevent leaks and overheating.

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Factors That Influence Tankless Water Heater Electricity Costs

Your tankless water heater’s electricity use depends mostly on how much hot water you run and how hot you set the water temperature.

After reaching the set temperature, the heater cycles on and off to maintain that temperature instead of running at full power continuously. Self-modulating models adjust their power draw instantly based on demand, so if you open just one faucet, the heater uses less electricity than when multiple taps run simultaneously.

Typical power needs range from 14 kW to 18 kW when heating water. That means your electrical panel must supply a 60-amp or higher dedicated circuit to handle the full load safely. Upgrading your panel might be necessary if it lacks this capacity.

Flow rate and usage duration directly influence energy consumption. Hot water flowing faster or for longer means the heater works more and draws more power. For example, a 4 GPM (gallons per minute) flow requires more electricity than 1 GPM. Intermittent on-demand use usually consumes less electricity than keeping a tank full, but frequent short uses can add up.

Household size and simultaneous hot water points affect total power demand. A single bathroom and kitchen sink running at once need more power than just one faucet. Larger families or homes with multiple simultaneous users will see higher electricity use.

How to Cut Electricity Costs of Your Tankless Water Heater

Tankless water heaters draw significant power—usually 14 kW to 18 kW—while heating water, so managing when and how they run cuts electricity bills effectively.

Energy Monitoring Help

14kW Tankless Water Heater Electric 240V

Product 3’s advanced temperature control and energy-efficient design make it easier to track and manage your tankless heater’s electricity use effectively.

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What to Do Next for Your Tankless Water Heater

Tankless electric water heaters typically cost between $500 and $1,500 for the unit alone, with installed prices often ranging from $1,000 to $3,000 depending on electrical upgrades and labor. Yes, they run solely on electricity and demand a dedicated circuit wired to your home’s electrical panel that can handle 14 to 18 kW at 240 volts.

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