Homeowners considering a new water heater often ask whether an electric tankless unit is the right choice. This question is especially relevant for homes with limited space, intermittent usage, or a desire to reduce energy consumption. The GreenBuildingAdvisor Q&A Spotlight on this topic examines a real-world case: a vacation homeowner facing very cold incoming water, limited gas availability, and existing photovoltaic panels. To make an informed decision, it helps to compare the electrical demands, installation costs, operating trade-offs, and practical alternatives. Understanding the full picture of water heater selection and installation for tank-type, tankless, and heat pump systems provides a useful starting point for evaluating what works in different home settings.
How Electric Tankless Water Heaters Work and Their Power Demands
Electric tankless water heaters, also called demand-type heaters, heat water directly as it flows through the unit. When a hot water tap opens, cold water passes over electric heating elements that rapidly raise the temperature. Unlike storage tanks, these units do not maintain a reservoir of preheated water, which eliminates standby heat loss entirely.
The key trade-off is the enormous electrical demand. Building science experts quoted in the GreenBuildingAdvisor article note that a whole-house electric tankless unit draws more than 25,000 watts and requires a dedicated 150-amp, 240-volt breaker. By comparison, a standard storage tank heater draws under 5,000 watts on a 30-amp breaker. For homes with combined hydronic heat and hot water systems where one tankless unit serves both space heating and domestic needs, the electrical load increases even further.
This high power draw creates two challenges. First, most existing homes have electrical service rated at 100 or 200 amps total. Adding a 150-amp breaker for a water heater leaves little capacity for other appliances. Second, upgrading the service panel and running heavy-gauge wiring can cost several thousand dollars before the heater itself is purchased. Utilities also face strain from these short, intense power bursts and some are responding with demand charges for high-peak customers.
Electric Tankless versus Storage Tank Water Heaters
Comparing electric tankless models with conventional storage tank heaters reveals meaningful differences in energy use, installation complexity, and long-term performance.
| Feature | Electric Tankless | Storage Tank (Electric) |
|---|---|---|
| Power draw | 25,000+ watts (150A breaker) | 4,500-5,500 watts (30A breaker) |
| Standby losses | None (heats on demand) | 30-50 kWh/month standby |
| Space required | Wall-mounted, compact | Floor space, 60 cm diameter |
| Flow rate limitation | Limited by inlet temperature | Limited by tank volume |
| Lifespan | 15-20 years | 8-12 years |
| First hour rating | Unlimited (continuous) | Limited to tank capacity |
| Installation complexity | High (panel upgrade needed) | Moderate |
The elimination of standby losses is the most frequently cited advantage of tankless technology. Storage tank heaters lose heat to the surrounding air through the tank walls even when no water is being drawn, costing 10 to 20 percent of total energy consumption in standby mode. A tankless unit avoids this entirely.
However, these energy savings must be weighed against the high upfront electrical work. As shown in reviews of the best electric tankless water heaters, unit prices range from $500 to $1,200 depending on flow capacity, but installation costs often exceed the unit cost when service upgrades are needed.
Flow rate is another practical difference. Tankless units are rate-limited by incoming water temperature. In northern climates where groundwater drops to 4-10 degrees Celsius in winter, the heater must work much harder, reducing effective flow rate by half or more. Storage tanks deliver hot water at a fixed temperature regardless of inlet conditions, though they are limited by total tank volume.
The True Cost of Installing an Electric Tankless System
Installation cost is often the deciding factor. For an electric tankless unit, costs include the heater itself, electrical service upgrades, wiring, breakers, permits, and labor.
- Electric tankless unit: $500 to $1,200
- Electrical panel upgrade (100A to 200A): $1,200 to $2,500
- Dedicated 150-amp breaker and wiring: $400 to $800
- Permits and inspection fees: $150 to $400
- Plumbing connections and mounting: $300 to $700
A professionally installed electric tankless system typically ranges from $2,500 to $5,500 or more, compared to $800 to $1,500 for a standard electric storage tank heater. The payback period from energy savings alone can extend well beyond the expected equipment lifespan. For homeowners exploring advanced water heater replacement options including tankless and heat pump systems, the analysis must factor in local utility rates, climate conditions, and available rebates, which can reduce the upfront cost by several hundred dollars in some regions.
Demand charges are an emerging concern. Utilities in several states are experimenting with rate structures based on peak power demand rather than total energy consumed. For an electric tankless unit drawing 25,000 watts in short bursts, even a modest demand charge of $5 per kilowatt of peak demand could add $125 or more per month to the electric bill. Homeowners should check with their local utility before purchasing.
Special Considerations for Vacation Homes and Intermittent Use
The GreenBuildingAdvisor article centers on a vacation home with intermittent use that occasionally hosts many guests at once. This pattern creates unique considerations.
For a vacation home used only a few weekends per month, a storage tank heater can be turned off at the breaker when the house is empty, eliminating standby losses entirely during unoccupied periods. This significantly reduces the energy efficiency advantage of a tankless unit, which still requires the electrical infrastructure to remain live even if not actively heating water.
Cold incoming water temperatures are another critical factor. Vacation homes in colder regions often have well water or uninsulated supply lines delivering water just above freezing. An electric tankless unit must overcome this temperature rise in real time, severely limiting the flow rate. When the homeowner needs hot water for multiple guests taking simultaneous showers, plus dishwashing and laundry, an electric tankless unit may struggle to keep up. Storage tank heaters handle this better by preheating a full volume of water. A well-sized 200-liter tank can supply several showers in sequence, recovering between uses. For a deeper comparison of how instantaneous hot water systems compare with traditional tank-style heaters across different usage scenarios, consider how simultaneous demand and recovery rates affect the overall experience.
Freeze protection is also a concern. Tankless units installed in unheated crawlspaces or garages require freeze protection features or indoor installation to prevent damage when the house is unoccupied in winter. Storage tank heaters have a large thermal mass that provides some buffer, though any installation in a cold climate must include proper insulation for exposed pipes.
Evaluating Alternatives and Making the Right Choice
Given the high electrical demands and installation costs, several alternatives deserve consideration depending on the home’s specific constraints.
- Heat pump water heaters: Use electricity to move heat from surrounding air into the water, achieving two to three times the efficiency of resistance heaters. They draw only 500 to 1,500 watts and require no panel upgrade in most homes, though they need adequate air volume and a condensate drain.
- Propane tankless water heaters: For homes without natural gas, propane-fired units provide high flow rates with minimal electrical demand limited to a control board and ignition system drawing under 100 watts. Proper combustion venting is required.
- Point-of-use tankless heaters: Instead of one whole-house unit, dedicated heaters at individual showers or sinks limit peak demand. Each draws 8,000 to 12,000 watts, and running only one or two at a time reduces the need for a massive panel upgrade.
- Larger storage tank heater: Increasing tank size from 150 to 200 or 250 liters provides more reserve capacity at a fraction of the installation cost of a tankless system.
For homes with existing solar PV systems, the calculus changes again. The vacation homeowner in the article already has panels, meaning electricity for water heating may be partially offset by solar generation. However, utilities increasingly apply demand charges to net-zero and solar homes to recover infrastructure costs. These charges apply to the peak draw when the tankless heater fires, potentially eroding the financial benefit of solar generation for water heating.
Proper water heater installation requires careful attention to sizing, connections, safety, and local code requirements regardless of the technology chosen. The best system matches the home’s usage pattern, climate, available fuel sources, and existing electrical infrastructure. A vacation home needing occasional bursts of hot water for a crowd may be better served by a larger storage tank heater that can be turned off between visits than by an expensive electric tankless system requiring full electrical service upgrades.
Conclusion
Whether an electric tankless water heater makes sense depends heavily on the specific circumstances. For new construction where electrical service can be designed from the ground up, and where continuous hot water delivery is a priority, an electric tankless unit can be a reasonable choice. The elimination of standby losses, the compact wall-mounted installation, and the longer equipment lifespan are genuine advantages.
For existing homes, particularly those with 100-amp electrical service, the cost of upgrading the panel often outweighs the energy savings. Vacation homes with intermittent use lose much of the standby loss advantage, since a tank heater can simply be turned off when empty. Cold incoming water temperatures can dramatically reduce flow rates, making simultaneous fixture use difficult. And emerging utility demand charges may add a significant ongoing cost.
Homeowners determined to go tankless with the budget for electrical upgrades will find the technology works well in the right application. Others may find that a heat pump water heater, a propane tankless unit, or simply a larger storage tank heater offers better value. Consulting a licensed electrician and plumbing professional to evaluate existing service, verify code requirements, and obtain accurate installation quotes is essential before making a final decision. Those interested in tankless water heater applications for combined space heating and domestic hot water needs should review the additional design requirements for such integrated systems.