TL;DR
An electric tankless water heater can be a great fit when you size it by your real peak hot-water demand (GPM) and your local temperature rise — and when your electrical service can actually support the unit’s amperage. If you’re in a cold-climate region, have frequent “two showers at once” use, or you’re on a 100A panel, you may be happier with a point-of-use strategy or a heat pump water heater instead.
What Electric Tankless Water Heaters Actually Are
An electric tankless water heater (also called an electric on-demand water heater) heats water only when you open a hot-water tap. Instead of keeping 40–80 gallons hot all day like a traditional tank, it uses electric resistance heating elements that ramp up when flow is detected. The unit measures incoming water temperature, outgoing temperature, and flow rate, then modulates power to try to hold your set temperature.
Functionally, the “formula” for getting a satisfying experience looks like this:
- Your needed hot-water flow (GPM) at the same time (example: one shower + a sink).
- Your required temperature rise (target hot temp minus incoming cold-water temp).
- The unit’s output curve (how many GPM it can deliver at that rise).
- Your electrical capacity (service size, available breaker space, wiring size, and load calculations).
The key is that “endless hot water” isn’t unlimited hot water at any flow. It’s endless hot water up to the unit’s capacity. When demand exceeds what the heater can add (especially in winter when incoming water is colder), the water typically goes lukewarm — because the unit can’t add enough heat at that flow rate.
Electric tankless also changes the delivery feel. With a tank, there’s hot water sitting ready at the heater. With tankless, the unit has to sense flow, energize elements, and then heated water still has to travel through your pipes. Long pipe runs still mean waiting, and that wait can feel more noticeable because there’s no “stored hot slug” at the start. The U.S. Department of Energy explains these sizing and usage realities for demand-type water heaters, and it’s worth reading before you buy: U.S. Department of Energy (Energy Saver) — Tankless or Demand-Type Water Heaters.
Finally: electric tankless is high-current equipment. Whole-house models commonly require multiple 240V double-pole breakers and large conductors. For safety and code compliance, plan on a licensed electrician (NEC-certified) to verify panel capacity, breaker sizing, and wiring methods per the NFPA (National Electrical Code).
Who Electric Tankless Water Heaters Fits Best
Electric tankless tends to make homeowners happiest in a few specific scenarios:
- You have modest simultaneous hot-water demand (one shower at a time, or a shower plus a low-flow faucet).
- You want to save space (condos, small mechanical rooms, tight utility closets, wall-mount installs).
- You’re okay planning around capacity—for example, avoiding running two showers and the dishwasher at the same time in winter.
- You can support the electrical load without risky DIY wiring or surprise panel/service upgrades.
- You’re open to maintenance if your water is hard (scale prevention + periodic flushing/descaling).
If you’re the kind of buyer who likes a predictable, controllable hot-water experience, the “right” electric tankless paired with the “right” electrical setup can feel clean and modern. But it’s not a set-it-and-forget-it category: it rewards planning.
One of the clearest “fit” signals we see in homeowner reports is that people are happy when they go in with realistic expectations about electrical demand and installation scope. For example: “Bought the 36 plus model, did not fully grasp the scope of installation. This thing potentially sucks up 150 amps, you might only have 200 amp service to your house!!” — verified buyer, 5 stars.
Who Should Skip Electric Tankless Water Heaters
Electric tankless is not a universal replacement for a tank. You should strongly consider skipping it (or limiting it to point-of-use) if any of these are true:
- You’re in a cold-climate region where incoming water gets very cold in winter. Big temperature rise = lower GPM unless you buy a very large (high kW) unit.
- You often need multiple simultaneous hot-water draws (two showers, laundry, dishwasher) and you don’t want to think about scheduling.
- Your home has limited electrical capacity (commonly 100A service, or a crowded panel with little spare capacity).
- Your water is hard and you don’t want maintenance. Scale can reduce output and cause performance complaints over time if you don’t manage it.
- Your main goal is lowest energy use. Many homes will see better efficiency outcomes with a heat pump (hybrid) tank water heater, depending on climate and install location. (Comparing efficiency metrics like UEF can help; see the U.S. Department of Energy resources on water heater efficiency and UEF.)
Another “skip it” signal is when owners expect tankless to fix slow hot-water delivery at far-away bathrooms. Tankless doesn’t shorten the pipe run; it still has to push hot water through the same plumbing. In some layouts, it can feel slower because there’s no stored hot water at the heater to start the trip.
And if you’re hoping to avoid professional installation, this category can be unforgiving. One critical part of buyer experience is that installation can be expensive or complex due to wiring and plumbing changes. As one reviewer put it: “It did cost a grand to install because I had to plumb and wire it.” — verified buyer, 4 stars.
Price and Value
Electric tankless water heater pricing breaks into two buckets:
- Equipment cost (the heater itself).
- Total installed cost (electrical work, plumbing changes, permits, and sometimes a panel/service upgrade).
On equipment alone, whole-house capable electric tankless units tend to land in the mid-to-high hundreds and up, depending on kW size and controls. For example, the Stiebel Eltron Tempra 36 Plus 36 kW Tankless Water Heater is typically shown in the $850 – $950 range for the unit itself.
Value-wise, the biggest “gotcha” is that the heater price is rarely the full story. Many homes need:
- Multiple dedicated 240V circuits (often multiple double-pole breakers).
- Correctly sized conductors (wire gauge matters at these loads).
- Load calculation / panel capacity confirmation (and sometimes a panel or service upgrade).
If your electrical service can support it without major upgrades, electric tankless can be a space-saving way to get continuous hot water for normal household patterns. If you’re forced into a panel upgrade to make it work, you should pause and compare total dollars against alternatives like a heat pump water heater (often very compelling for efficiency) or targeted point-of-use heaters to cover just the fixtures that need help.
Common Mistakes When Trying Electric Tankless Water Heaters
Most problems people blame on “tankless” are really sizing, electrical, or expectation issues. Here are the mistakes we see most often in homeowner reports and installer feedback:
- Sizing by “whole house” marketing instead of charts. You want GPM at your temperature rise. Incoming water temp can be dramatically different in Minnesota vs. Florida, and it changes seasonally.
- Underestimating the electrical reality. Whole-house electric tankless can demand an enormous amount of current. If you’re near the limits of your service, this can turn into a panel/service upgrade conversation fast.
- Assuming tankless solves slow hot water. Waiting is usually a plumbing distance/recirculation/insulation issue, not a storage-vs-tankless issue.
- Ignoring hard water. Scale buildup reduces heat transfer, which can show up as reduced flow, lukewarm output, or more frequent service needs.
- DIYing high-amperage wiring. These installs commonly involve multiple 240V circuits. A licensed electrician (NEC-certified) should verify breaker sizing, wire sizing, and code-compliant disconnecting means per the NFPA (National Electrical Code).
The most common “wish I’d known that” is how big the electrical load can be. One owner summed it up bluntly: “Bought the 36 plus model, did not fully grasp the scope of installation. This thing potentially sucks up 150 amps, you might only have 200 amp service to your house!!” — verified buyer, 5 stars.
FAQ
How do I size an electric tankless water heater for my home?
Size it in two steps: (1) calculate your peak simultaneous hot-water flow in GPM (for example, one shower plus a sink), and (2) estimate your temperature rise (desired hot-water temp minus incoming cold-water temp). Then use the manufacturer’s performance chart to confirm the unit can deliver your required GPM at that rise. The U.S. Department of Energy’s tankless water heater guide explains why flow rate and temperature rise are the sizing foundation.
Will an electric tankless water heater work with a 100-amp service?
Sometimes, but it’s often tight for a whole-house unit. Many whole-house electric tankless heaters require multiple 240V breakers and very high total amperage, which can exceed what a 100A service can safely support after load calculations. If you’re on 100A, ask a licensed electrician (NEC-certified) to run a load calculation and check your panel capacity before you buy, using requirements consistent with the NFPA (National Electrical Code). If capacity is limited, consider a smaller point-of-use heater near a problem bathroom or a heat pump water heater as alternatives.
Do electric tankless water heaters save money on energy bills?
They can reduce standby losses because they’re not keeping a tank of water hot 24/7. But “lower bills” isn’t guaranteed — your results depend on hot-water usage patterns, incoming water temperature, and electricity rates. For comparing water heaters more broadly, it helps to look at efficiency metrics like UEF; the U.S. Department of Energy is the right reference point for understanding those ratings.
Why does it take longer to get hot water with a tankless?
Most of the wait is still your plumbing: the hot water has to travel from the heater to the faucet through the same pipe run as before. With tankless, there’s also a short ramp-up period while the unit senses flow and energizes the heating elements. If wait time is your main complaint, focus on shortening pipe runs where possible, insulating hot-water lines, or discussing a properly designed recirculation approach with a licensed plumber.
How often do I need to descale an electric tankless water heater?
It depends mostly on water hardness and how much hot water you use. In hard-water areas, more frequent descaling/flushes are common to keep heat transfer strong and maintain flow and temperature stability. Follow your manufacturer’s maintenance guidance to protect performance and avoid warranty issues; if you’re unsure about your local water hardness, your utility’s water quality report or a simple home test can help you decide how aggressive to be.
Can I run two showers at once on an electric tankless?
Maybe — but only if the unit can deliver enough GPM at your required temperature rise, and your electrical service can support the heater’s full draw. Two showers can easily push you into a higher-capacity (higher kW) unit, especially in winter in colder regions. This is where checking the performance chart matters more than “whole-house” labels.
Bottom Line
Electric tankless water heaters work best when you pick a unit based on GPM at your local temperature rise and you confirm — up front — that your electrical panel/service can safely support the load. If you can’t (or don’t want to) accommodate the electrical and maintenance realities, you’ll likely be happier with point-of-use heaters for specific fixtures or a heat pump water heater for overall efficiency.
