Quick links
- How an Electric Tankless Heater Works
- Whole House Electric Tankless Water Heaters
- Sizing by Flow Rate and Temperature Rise
- Small Electric Units: 120V, Under Sink and Portable
- Outdoor and Mobile Home Use
- Installing an Electric Tankless Heater
- Are Electric Tankless Water Heaters Good and Efficient?
- Cost Factors for an Electric Tankless Installation
- Which Homes Suit Electric Tankless, and Which Do Not
- Combining Electric Tankless With Fixtures and Remodels
- Maintenance and Common Problems
- Where You Can Get Help
- Related Plumbing Help
- Frequently Asked Questions
An electric tankless water heater heats water as it flows past heating elements, with no burner, no flue and no storage tank. Its big requirement is electrical: a whole-house unit can draw more power than many older panels have to spare, so the first job is an electrical check, and the second is a flow-rate check against how you actually use hot water.
That makes the question less about the heater and more about the house. Panel capacity, wire size, incoming water temperature and the number of fixtures running together decide whether one unit will do, whether you need two, or whether a small unit at a single sink is smarter. Here is how to work through it.
How an Electric Tankless Heater Works
An electric on demand water heater waits until a tap opens. A flow sensor senses moving water and switches on heating elements, which warm the water as it passes through. Close the tap, and the elements shut off. It is sometimes called an electric instant water heater, an electric instant hot water heater or an electric continuous water heater, and all mean the same idea: heat only when hot water is being used.
Are tankless water heaters gas or electric?
Both exist. Are tankless water heaters gas or electric is a common question, and the answer is that each fuel has trade-offs. Gas units use burners and need venting. Electric units need no vent but need a lot of electrical capacity. The propane tankless water heater covers the gas side, and the tankless water heater installation and cost compares the two more broadly.
Do gas tankless water heaters need electricity?
Yes, gas tankless models also need a small amount of power for the fan, igniter and controls. Do gas tankless water heaters need electricity is worth knowing, because it means a power outage affects both types, even though the demand is very different.
Electric tankless boiler
An electric tankless boiler is a related idea for hydronic heating: it warms circulating water for radiators or baseboard without a tank. It is not the same as a domestic hot water unit, though some setups feed both. A plumber will want to look at the whole system.
Whole House Electric Tankless Water Heaters
A whole house electric tankless hot water heater, also called a whole house water heater tankless or whole house on demand electric water heater, is sized to serve several fixtures at once. Because electric elements pull large current, these units may need heavy-gauge wire and multiple double-pole breakers.
What the electrical load looks like
Large units are described in kilowatts. You may see an 18kw-class unit, for example, and the amperage it needs is in the manufacturer's spec, not a number to guess. A 30 amp on demand water heater usually refers to a smaller model that serves a bathroom or a low-demand home. The higher the output, the more panel space and wire size matter.
Panel and service check
- Compare the unit's amp draw with the space left in the main panel
- Check the main breaker rating against the whole household load
- Look at wire runs, since long runs increase the size of wire needed
- Ask whether a service upgrade is possible or needed
A whole house tankless hot water heater can be a poor fit when the panel cannot support it, and a plumber and electrician will tell you that before you buy.
Ready to get a quote? Availability and pricing are confirmed by phone.
Call 417-261-5030Sizing by Flow Rate and Temperature Rise
Flow rate, measured in gallons per minute, is what a tankless unit is rated on. Heating water from cold takes more power than heating water that is already warm, so winter performance can be lower than summer.
Two showers at once
People often ask whether a single unit can handle two showers. The honest answer depends on the incoming water temperature, the showerheads' flow and the unit's output. Even a 7 gpm tankless water heater label is only meaningful at a stated temperature rise. Have the installer size it against your coldest month.
Questions to ask
- What is the rated flow at my coldest incoming water temperature?
- How many fixtures do we run at once?
- Do low-flow fixtures change the answer?
- Would two smaller units serve the house better than one big one?
Small Electric Units: 120V, Under Sink and Portable
Not every electric tankless heater is whole house. Small models serve one fixture.
120V tankless water heater
A 120v tankless water heater, also called 120v tankless water heater electric, 120 volt tankless hot water heater, 120 volt instant water heater or tankless 120 volt water heaters, plugs into a standard circuit. Because power is limited, these units raise water temperature modestly and deliver low flow. They suit hand washing, not showers.
Under sink electric heaters
An under sink water heater, also sold as an under sink tankless water heater, under counter water heater or under sink electric water heater, sits in a cabinet and gives fast hot water at one faucet. The point of use water heater goes deeper on the sink-level choice.
Portable and small units
A portable electric hot water heater or portable water heater electric is meant for temporary or off-grid use. A small electric tankless hot water heater may suit a workshop or camper. An instant water heater for shower is worth checking carefully; a plug-in unit that promises a full shower may not deliver, and must be installed by someone who understands the electrical safety around water.
Outdoor and Mobile Home Use
An outdoor electric tankless water heater is built for exterior walls, in cabins or outbuildings, but freezing weather and moisture are the enemies. A tankless water heater for mobile home use is also common, because the unit is compact and needs no vent. Manufactured housing has its own electrical and mounting rules, so confirm the model is approved for that use.
Installing an Electric Tankless Heater
Water heater installation covers the common connections. For tankless electric, the specifics are:
- Confirm panel capacity and available breaker spaces.
- Run properly sized wire and install the correct double-pole breakers.
- Mount the unit on a wall with clearances and service access.
- Connect the water lines with isolation valves for flushing.
- Fill, purge air, then power on and test flow and temperature.
Wiring safety
Electricity and water do not mix. If you are asked to open a unit or touch wiring, do not do it with power on. Wiring and breaker work is for a professional, and a scorched breaker or warm wire is a reason to stop and call.
Replacing a tank with electric tankless
People who search for instant water heater replacement are often replacing a failed tank. Start with how water heater replacement normally goes, then consider whether the electrical and plumbing work for tankless is worth it in your house.
Water still running or a smell of gas? Act first, then call.
Call 417-261-5030Are Electric Tankless Water Heaters Good and Efficient?
Are electric tankless water heaters good depends on your goals. They have no standby loss and are compact, and elements convert nearly all of their electricity to heat. Are electric tankless water heaters efficient in practice? In terms of turning power into heat, generally yes. Whether they are cheaper to run depends on your electricity rates and hot water habits.
Pros
- No tank to leak or rust out
- Compact, wall-mounted design
- No vent, flue or fuel line
- Continuous hot water within the flow limit
Cons
- High electrical demand
- Lower flow in cold climates
- Scale buildup in hard water
- Upfront cost and panel upgrades can add up
Reviews and brand names
Electric water heater reviews are worth reading with care, since a review rarely reflects your panel, your water or your flow needs. AO Smith and other tankless water heater AO Smith and AO Smith tankless water heaters searches turn up familiar names, and the "best" model for a neighbor may not suit you. Look for the best electric tankless water heaters in terms of fit, warranty and how easily parts and service are available.
Cost Factors for an Electric Tankless Installation
Electric tankless water heater cost depends on the unit, panel work, wire, plumbing changes and access. Prices are confirmed by phone, and your quote should list electrical work separately. A best electric on demand water heater or best whole house electric tankless water heater is not necessarily the most expensive one.
- Size and output of the unit
- Panel or service upgrades
- Wire gauge and length
- Plumbing modifications and valves
- Permit and inspection
- Removal of the old tank
For the general picture, see what plumbers charge and why. If your old tank is leaking now, emergency plumbing is the priority.
Which Homes Suit Electric Tankless, and Which Do Not
Electric tankless suits homes where the electrical service is generous, the household is small to medium, and gas is unavailable or unwanted. It struggles in large households in cold regions, where incoming water is very cold and demand peaks are high.
Good fits
- Condos and apartments where venting a gas unit is not allowed
- Homes with a modern 200-amp service and spare breaker spaces
- Additions, garages or guest suites far from the main heater
- Small households with staggered hot water use
- Homes moving away from gas appliances
Poor fits
- Older houses with a small panel and no room for an upgrade
- Large families who run several showers, laundry and a dishwasher together
- Very cold groundwater regions, unless multiple units are planned
- Rentals where the landlord will not approve panel changes
Landlord and tenant notes
Landlords weighing tankless for an apartment building should think about individual units versus a central system, since each has different electrical and maintenance demands. Tenants should not modify wiring or plumbing on their own; report a failed heater to the owner or manager.
Combining Electric Tankless With Fixtures and Remodels
Tankless heaters change where hot water is made, which can be useful when other plumbing work is happening. During a bathroom remodel a small unit near a new shower or vanity can shorten the wait for hot water. Swapping a fixture, such as a kitchen faucet replacement, is a moment to consider an under-sink unit at that location.
Planning the layout
- Keep the heater close to the fixtures it serves to reduce wait time
- Leave clear space and access for servicing and flushing
- Put isolation valves on both water lines
- Plan the electrical route before the walls are closed up
Broader jobs like these sit under plumbing installation, and a plumber can coordinate with an electrician so the two trades do not work at cross purposes.
Not sure what you need? Call and we will point you to the right help.
Call 417-261-5030Maintenance and Common Problems
Scale
Hard water leaves mineral scale on elements and in inlet screens, reducing flow and heating. Descaling or a filter helps, depending on your water.
Symptoms to note
Some of these are minor and some need a technician. If you find a wet area under the unit, see leak detection for tracing the source.
- Water that fluctuates between hot and cold
- Error codes on the display
- A breaker that trips when the unit starts
- Reduced flow at fixtures
- Warm spots or discoloration on wiring or the breaker
- Clicking or humming from the unit that is new
For diagnosis, tankless water heater repair explains what technicians check.
Where You Can Get Electric Tankless Water Heater Installation Help
Plumbing calls are taken for 21 states, 1,511 cities and 3,769 ZIP codes. Pick your state, or look at a sample city and ZIP for each state; coverage for your exact address is confirmed by phone.
- Arizona
- California
- Colorado
- Connecticut
- Florida
- Georgia
- Idaho
- Illinois
- Maine
- Massachusetts
- Michigan
- Minnesota
- Missouri
- New Hampshire
- New Jersey
- New York
- North Carolina
- Ohio
- Texas
- Virginia
- Washington
| City | ZIP codes and places |
|---|---|
| Mesa, AZ | 85203 about 1.4 miles from HoHoKam Stadium; about 1.5 miles from Fitch Park 85211 about 2 miles from HoHoKam Stadium; about 2.7 miles from Sloan Park |
| Pasadena, CA | 91101 near Pacific Asia Museum; near Fuller Theological Seminary 91102 near Pasadena City Hall; near Fuller Theological Seminary |
| Colorado Springs, CO | 80901 near Colorado Springs Fine Arts Center; about 1 mile from Colorado College 80906 about 1.4 miles from Broadmoor World Arena; about 1.6 miles from World Figure Skating Hall of Fame |
| Groton, CT | 06340 about 2.4 miles from United States Coast Guard Academy; about 2.6 miles from Mitchell College 06349 about 1.6 miles from Connecticut College; about 1.7 miles from Connecticut College Arboretum |
| Hialeah, FL | 33002 about 2 miles from Amelia Earhart Park; about 4.5 miles from Miami International Airport 33010 about 2.8 miles from Miami International Airport; about 3.7 miles from Amelia Earhart Park |
| Marietta, GA | 30006 near Strand Theatre; about 1.9 miles from Southern Polytechnic State University 30007 about 2.3 miles from Georgia Military Institute; about 2.9 miles from Southern Polytechnic State University |
| Eagle, ID | 83616 about 8 miles from Idaho Aquarium; about 10 miles from Idaho Central Arena |
| Palatine, IL | 60038 near Arlington Park; about 7 miles from McDonald's #1 Store Museum 60055 near Arlington Park; about 7 miles from McDonald's #1 Store Museum |
| Biddeford Pool, ME | 04006 about 2.5 miles from University of New England; about 7 miles from Funtown Splashtown USA |
| Wakefield, MA | 02129 near Monument Square Park; near Thompson Square 02131 about 1.2 miles from Faulkner Hospital; about 1.3 miles from Bussey Institution |
| Clinton Township, MI | 48035 about 8 miles from Jimmy John's Field; about 14 miles from Lake Saint Clair |
| Maple Plain, MN | 55359 about 7 miles from Crown College; about 7 miles from Lake Minnetonka |
| O Fallon, MO | 63366 about 4.9 miles from Midwest University; about 6 miles from Wentzville Ice Arena 63368 about 8 miles from Midwest University; about 8 miles from Wentzville Ice Arena |
| Dover, NH | 03820 about 4.2 miles from Whittemore Center; about 4.3 miles from University of New Hampshire 03821 about 4.5 miles from Powderhouse Hill; about 5 miles from Whittemore Center |
| Jersey City, NJ | 07097 near Mana Contemporary; near Saint Peter's University 07302 near Hamilton Park; near Headroom LGBTQ+ Lounge |
| Manhasset, NY | 11030 near Manhasset Valley Park; about 1.3 miles from Flower Hill Village Park |
| Kannapolis, NC | 28081 about 3.9 miles from CMC-NorthEast Stadium; about 11 miles from Charlotte Motor Speedway 28082 about 8 miles from Charlotte Motor Speedway; about 19 miles from Spectrum Center |
| Westerville, OH | 43081 about 1.6 miles from Otterbein University; about 8 miles from Historic Crew Stadium 43086 near Huntington Park; near Nationwide Arena |
| Plano, TX | 75023 about 2.1 miles from John Clark Field; about 4.9 miles from University of Texas at Dallas 75024 about 1 mile from Children's Medical Center at Legacy; about 2.6 miles from Riders Field |
| Yorktown, VA | 23690 about 1.9 miles from Endview Plantation Historic Site; about 2.7 miles from Virginia Institute of Marine Science 23691 about 2.9 miles from Virginia Institute of Marine Science; about 3 miles from Endview Plantation Historic Site |
| Lakewood, WA | 98439 about 1.7 miles from McChord Field; about 2.5 miles from American Lake 98496 about 2.5 miles from McChord Field; about 2.7 miles from Fort Steilacoom |
Frequently Asked Questions
How does an electric tankless water heater work?
Water flowing through the unit trips a flow sensor, which turns on electric heating elements. The elements heat the water as it passes, and the unit shuts off when the tap closes. There is no tank, so hot water lasts as long as the unit can keep up with the flow you are asking for.
Do I need a special circuit for an electric tankless water heater?
Whole house units typically need a dedicated, heavy-gauge circuit and one or more double-pole breakers. Small 120V units plug into standard circuits but heat less. The exact requirements are on the unit's rating label. An electrician or plumber should check your panel before you buy.
Can an electric tankless heater run two showers?
It depends on the unit's rated output, the incoming water temperature and the flow of your showerheads. Some can, especially in warm climates or with low-flow heads, and others cannot. Ask for sizing against your coldest incoming water, not a summer estimate.
Are tankless water heaters gas or electric?
They come in both. Gas and propane units burn fuel and need venting; electric units have no vent but need substantial power. The right choice depends on what your home has and what upgrades are practical.
Do 120V tankless water heaters work for a shower?
Generally not well. A plug-in unit has limited power, so it raises water temperature modestly at low flow, which suits a hand basin. A shower usually needs a larger, hardwired unit.
What is an under sink tankless water heater good for?
It gives quick hot water at a distant sink so you do not wait for the main heater. It is best for hand washing and small tasks, not for filling a tub.
Are electric tankless water heaters efficient?
They convert nearly all the electricity they use into heat and avoid tank standby loss. Whether they save money depends on your electric rates and usage. Compare based on your own bills.
Can I install an electric tankless water heater myself?
Small plug-in units can be simple, but a whole house unit involves high-current wiring, breaker work and often a permit. Errors can be dangerous. Hire a professional for anything hardwired.
Does a tankless heater work in a mobile home?
Yes, many are used there, as they are compact and need no vent. Confirm the model is approved for manufactured housing and check the electrical service can support it.
How often should I descale an electric tankless heater?
It depends on your water hardness and how much hot water you use. In hard water areas, yearly service is common. Your plumber can suggest a schedule and install isolation valves to make flushing easier.
Ready to talk to a plumber? Call 417-261-5030.
Call 417-261-5030