Electric Tankless Water Heater in Phoenix? What the Electrical Needs

An electric tankless water heater in Phoenix can need more electrical capacity than almost anything else in your house. Before you buy one, it helps to know how much power it draws, whether your panel can carry it, and how it compares with a standard tank or a heat pump water heater. Here is what we look at when a homeowner calls about a water heater change.

Electric tankless water heater electrical requirements

A tankless heater warms water only while it flows, so it has to heat it fast. That takes a lot of power at once. A small point-of-use unit under a sink may need one modest circuit. A whole-house electric tankless unit is a different animal:

• Several large circuits. Whole-house models often need two, three or even four 240-volt circuits, each on its own double-pole breaker. The installation manual lists exactly how many and what size.
• Heavy wire. Each of those circuits needs wire sized to its breaker. That's thick, stiff copper, and the run from the panel to the heater has to be planned around it.
• Panel space. Every double-pole breaker takes two spaces. Three circuits means six open spaces, which many older Phoenix panels simply don't have.
• Service capacity. When the heater fires at full output, it can draw more current than your central air conditioner. On a July afternoon with the AC, pool pump and dryer running, that adds up fast.

Tank, tankless or heat pump: how the electrical compares

Standard electric tank. Most run on one dedicated 240-volt circuit. If you're replacing a tank with a similar tank, the existing circuit is usually reused after a quick check of the wire, breaker and connections.

Heat pump water heater. These pull heat from the surrounding air, so they use far less electricity than a standard tank to make the same hot water. Many run on a 240-volt circuit similar to a standard tank. Some newer models are made to run on 120 volts, which can make a switch from gas easier. Check the manual for the circuit it requires.

Electric tankless. The biggest electrical demand of the three, as described above. It saves floor space and never runs out of hot water, but the wiring and panel side is a real project.

Gas tankless. If you're keeping gas, most gas tankless units still need a 120-volt outlet or circuit for their controls and fan. That's a small job, but it should be planned so you don't end up with an extension cord in the garage.

Will a tankless water heater overload my panel?

It might. This is the question that matters most, and the answer comes from a load calculation, not from looking at the main breaker size. The calculation adds up what your home already uses, including one or two AC systems, the range, the dryer and pool equipment, then adds the new heater. Our post on AC load and your electrical panel walks through how that works in a Phoenix home.

If the panel has capacity but no open spaces, a subpanel may solve it. Our subpanel vs panel upgrade post explains the difference. If the service itself can't carry a whole-house tankless unit, you're looking at a service upgrade. Our 200-amp vs 400-amp guide covers when a bigger service makes sense, and the panel upgrade cost guide explains what drives the price. Sometimes the honest answer is that a heat pump water heater or a smaller tankless unit fits your home better than a whole-house tankless model.

Phoenix details that change the plan

• Winter sizing. In summer, the water coming into a Valley home is warm, so a tankless heater barely has to work. In winter the incoming water is colder and the heater has to raise it much more. Size the unit, and its circuits, for winter, not for July.
• Garage heat and heat pump units. ENERGY STAR's heat pump water heater page recommends a space that stays between 40 and 90 degrees year-round. Many Phoenix garages run hotter than that in summer. Check the manufacturer's operating range before you choose the garage as the location.
• Hard water. Valley water leaves scale behind, and tankless heat exchangers are sensitive to it. That's a plumbing issue, but plan for service access around the unit so it can be flushed without working around live wiring.
• Older panels. Many 1960s and 70s ranch homes have panels with little spare space. If yours is a brand known for problems, like Federal Pacific or Zinsco, replace it before adding a big new load.

Water heater electrical in Paradise Valley

In Paradise Valley, homes are often large and spread out, with more than one water heater and long distances between the panel and the mechanical room or garage. That makes wire size and routing a bigger part of the job. Paradise Valley is its own town, so permits go through the Town rather than the City of Phoenix. Many homes there also have pool equipment, multiple AC systems and sometimes an EV charger, which is exactly when a load calculation should come before the purchase.

Permits and who does what

Replacing a water heater usually involves both a plumber and an electrician, and sometimes one company handles both. New circuits and panel changes are permitted electrical work in Phoenix and the surrounding cities. Ask up front who is pulling which permit, so the electrical side doesn't get skipped. If a service upgrade is part of the plan, our panel upgrades page explains how we handle the utility coordination.

Get the water heater circuits done right

If you're planning an electric tankless or heat pump water heater, send us the model number and a photo of your panel with the door open, and we'll tell you what it takes. B and D Electric LLC is licensed and bonded, Arizona ROC 361086, and our two owners have more than 40 years of combined experience. Call or text (480) 828-1181, or request an estimate.