EcoSmart Tankless Water Heater Guide: Sizing, Wiring and Real Running Costs

An electric tankless water heater heats water only while a tap is open, using heating elements that switch on when flow is detected. The EcoSmart name is one of the brands people search for when they want that kind of unit, and this guide is not a ranking of specific models. It covers the decisions that matter whichever model you shortlist: how much power you need, whether your home can supply it, what installation tends to cost, and what to verify on the listing before you pay.

The short version is that tankless electric heaters work best in homes with modest hot water demand, mild incoming water temperatures, or a point-of-use job such as a distant bathroom sink. They are harder to justify in a large household in a cold climate, because the electrical demand can be very large. Everything below is general information based on published engineering formulas and typical manufacturer documentation. Where specifics vary by model, we tell you to check the listing.

Quick decision table

What “tankless” does and does not change

A stored-tank heater keeps dozens of gallons hot all day and loses a little heat through the tank walls. A tankless unit removes that standby loss, which is where any savings come from. It does not make the heating itself cheaper: converting electricity into heat with a resistance element is close to fully efficient either way, so the energy needed to raise a gallon by a given number of degrees is the same.

What changes is the supply side. A tank can deliver a large burst of hot water because it stores energy over hours. A tankless unit has to deliver all of that energy in the moment. That is why electric tankless heaters are rated in kilowatts and why the same unit can feel generous in July and disappointing in January.

It also changes the experience. You will not run out of hot water during a long single shower, which is the classic tank complaint. But you can overload a unit by opening two showers at once, and a very low flow, such as a barely open tap, may not trigger the heating elements at all. Look for the minimum activation flow in the specifications.

Types you will run into

Product pages for this brand and its competitors generally fall into a few families. The names differ, so treat these as categories to look for rather than exact product lines.

• Whole-home electric units. Wall-mounted, high kilowatt ratings, often needing several breakers or very large single circuits. Intended to serve more than one fixture.
• Point-of-use units. Smaller, lower current, meant for a single sink, bar, garage or distant bathroom to cut the wait for hot water.
• Mini-tank hybrids. A small stored volume with elements, sometimes listed under the same family. These behave differently from true on-demand units, so read the description carefully.
• Outdoor or special-purpose units. Rated for a particular environment. Check the listing for the intended location and any enclosure requirements.

Some listings bundle a unit with a mounting kit or fittings; others sell the heater alone. Compare what is actually in the box, because missing parts add to the installed cost.

How to size a unit: flow rate and temperature rise

Two numbers decide the size. The first is the flow you want at the same moment, measured in gallons per minute. The second is the temperature rise: the difference between your coldest incoming water and your target. Many people set showers near 105 degrees Fahrenheit, but you should use the temperature you actually run.

A rule of thumb from basic physics is that power in kilowatts is roughly 0.147 times flow in gallons per minute times temperature rise in degrees Fahrenheit, assuming near-total conversion of electricity to heat. Manufacturers publish their own charts; use those for the final call.

Worked example (assumptions, not a promise for any model). Take one shower at 2.0 gallons per minute, incoming water at 50 degrees in autumn and a target of 105 degrees. The rise is 55 degrees, so you need about 0.147 x 2.0 x 55, or 16.2 kW. At 240 volts that is about 67 amps. Because continuous loads are typically sized at 125 percent, an electrician would be looking at roughly an 85 to 90 amp circuit capacity for that one shower. Now change the winter groundwater to 40 degrees: the rise is 65 degrees and the need grows to about 19 kW, or around 80 amps before the safety margin.

That arithmetic is the reason many whole-home electric units are marketed with a “flow at a given rise” table instead of a single gallons-per-minute number. Find the table on the listing or the manual, locate your coldest-month rise, and read off the flow it can actually deliver.

Electrical requirements: the part that surprises people

Before you compare brands, check whether your home can supply the load. Typical items to confirm with a licensed electrician are the service size, the spare capacity left after existing loads, the number of free breaker slots, the wire gauge and the run length from panel to heater. A high-kilowatt unit can require a service upgrade, which often costs far more than the heater.

Models are usually specified for 240 volts, with one or more dedicated double-pole breakers. Some use multiple smaller circuits instead of one huge one, which can make wiring easier but needs more panel space. Compare the “minimum breaker size” and “wire gauge” lines across listings, since a lower-power model may avoid a panel change entirely.

Safety matters here. Installation of electrical and plumbing appliances should be done by a qualified professional, and permits are often required. Follow the manufacturer’s instructions and local codes. A mis-sized breaker or loose terminal on a high-current circuit is a fire risk.

What installation can cost: a labeled estimate

We cannot quote your local prices, and any number published online is an estimate. A reasonable way to plan is to split the budget into the heater, the electrical work and the plumbing work, then request written quotes for each.

As a loose assumption for planning, treat the installed cost as the heater price plus a “wiring and labor” line that could be a few hundred dollars in the best case and well over a thousand if the panel needs work. If a contractor quotes a figure far from your own estimate, ask which line items explain the gap.

Running cost: a simple worked example

Suppose a household has one 8-minute shower at 2.0 gallons per minute, so 16 gallons. Raising 16 gallons by 55 degrees takes about 16 x 8.34 x 55 = 7,340 BTU, which is about 2.15 kWh. If your electricity price is 16 cents per kWh (an assumption for the example), that shower costs roughly 34 cents in heating energy. Multiply by showers per day and the number of days to get a monthly figure, then compare with what you pay now.

The same calculation for a tank heater gives a similar number for the water itself, plus standby losses that depend on tank insulation and room temperature. If your current tank is old and poorly insulated, the gap can be meaningful; if it is well insulated, the difference may be small. Treat any claimed percentage saving on a listing as a marketing figure until you run your own numbers.

Also check your utility’s rate structure. Time-of-use plans and demand charges can change the economics of a heater that pulls a large current for short bursts.

Water quality, scale and maintenance

Tankless heaters push water through narrow passages across hot surfaces, so mineral scale is a real concern in hard-water areas. Scale insulates elements, lowers output and can trigger error codes or shorten life. Manuals often give a maximum hardness, a recommended flush interval and inlet-filter cleaning steps.

If you are already thinking about water treatment for the whole house, our guide to whole-house carbon water filters explains what carbon filtration does and does not remove. Note that carbon media is mainly for taste, chlorine and some organic compounds, not for hardness, so do not assume it protects heating elements from scale.

Plan maintenance before you buy. Ask whether isolation valves for flushing are included, how the inlet screen is cleaned, and what the warranty says about water conditions. If a warranty excludes damage from scale, a softener may be part of the true cost of ownership.

Who should choose one, and who should skip

Good fit: a small household in a mild or warm climate; a bathroom far from the main heater where waiting for hot water wastes time; a workshop, garage or guest suite where a full tank is overkill; anyone whose old tank has failed and whose panel has room for the new circuit.

Weak fit: a large household with simultaneous showers in a cold region; a home with a small electrical service and no budget for an upgrade; a rental where you cannot alter the wiring; a house with very hard water and no plan for scale control. In those cases a stored tank, a heat-pump water heater or a gas model may deliver a better result, and a qualified plumber can compare them for your house.

Checklist before you buy

• Write down your coldest incoming water temperature and the highest simultaneous flow you need.
• Read the manufacturer’s flow-versus-temperature-rise table for the exact model, not the headline kilowatt number.
• Confirm voltage, amperage, breaker size and wire gauge, and show them to an electrician.
• Check the minimum activation flow, the maximum working pressure and the inlet and outlet fitting sizes.
• Look at the warranty length for the heat exchanger or elements, and any water-quality conditions attached.
• Confirm whether the listing is a whole-home unit, a point-of-use unit or a mini-tank; titles can blur the categories.
• Ask what is in the box, and what installation parts you must buy separately.
• Check the return policy and who services the unit if a part fails.

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Frequently asked questions

How do I know what size of electric tankless heater I need?

Start with the flow you want at the same time (for example one shower at about 2 gallons per minute) and the temperature rise from your coldest incoming water to your target. Multiply gallons per minute by degrees of rise and by roughly 0.147 to estimate kilowatts. Colder groundwater in winter needs more power, so size for the coldest month, not the average one.

Will it run on my existing electrical panel?

Possibly not. Whole-house electric units can draw more current than many older panels have spare, and they usually need dedicated double-pole breakers and heavy-gauge wiring. A licensed electrician should do a load calculation and install the circuit. Smaller point-of-use models draw less, but still check the listing for the required amperage and follow the manufacturer’s instructions and local codes.

Does a tankless heater really save money?

It can avoid standby heat loss from a stored tank, but electric resistance heating costs the same per unit of heat whether it is stored or instant. Savings depend on your hot water habits, electricity rates and the old tank’s condition. Any figure you see is an estimate until you run your own numbers using your usage and utility rate.

Do I need a water softener with a tankless heater?

Hard water leaves scale on heating elements and in small passages, which can reduce output and shorten life. Many manufacturers specify a maximum hardness or recommend periodic flushing or descaling. Check the product manual for its water-quality limits and whether scale damage affects the warranty, and consider a softener or filter if your supply is hard.

Can I install one myself?

Plumbing and electrical connections should be handled by qualified professionals. A mistake in wiring, grounding or relief provisions can cause fire, shock or scalding, and a DIY job can also void the warranty or fail inspection. Permits are often required. Ask installers for a written quote that covers the breaker, wire, fittings and any panel work.