Tankless water heaters promise endless hot water and lower energy bills, and for many Aiken homeowners they deliver on both counts. But before you can enjoy those benefits, there is a critical step that catches most people off guard: the electrical work. Unlike a traditional tank water heater that plugs into a single circuit or runs on gas alone, an electric tankless water heater has serious electrical demands that often require significant upgrades to your home's wiring and panel. If you are considering a tankless water heater for your Aiken home, here is what you need to know about the electrical side before you buy.
Why Electric Tankless Water Heaters Need So Much Power
A traditional tank water heater stores 40 to 50 gallons of hot water and heats it gradually over time. The heating element draws a moderate amount of electricity because it has hours to bring water up to temperature. A tankless unit works completely differently. It heats water on demand, the instant you turn on a faucet. To raise incoming water from its ground temperature to your desired output temperature in the few seconds it takes water to pass through the unit, the heating elements must produce an enormous amount of heat very quickly.
In Aiken, incoming water temperature typically ranges from around 55 degrees in winter to 75 degrees in summer. A whole-house electric tankless unit needs to raise that water to 120 degrees or more while pushing it through at 3 to 5 gallons per minute. The result is power consumption that ranges from 18 kilowatts on the low end to 36 kilowatts or more for larger units. To put that in perspective, 36 kilowatts is roughly the same as running nine electric ovens at the same time.
Multiple 40-Amp Circuits Are Standard
Most whole-house electric tankless water heaters require between two and four dedicated 40-amp or 50-amp circuits. A mid-range unit rated at 24 kilowatts typically needs three 40-amp double-pole breakers. A larger 36-kilowatt unit may need four. Each of these circuits must run from your main electrical panel directly to the water heater with no other outlets, fixtures, or devices sharing the circuit.
This is not a matter of preference or over-engineering. The manufacturer's installation manual specifies exactly how many circuits the unit requires, and this specification is backed by the National Electrical Code. Installing a tankless water heater on fewer circuits than required will cause the unit to underperform, trip breakers constantly, or fail to heat water to the desired temperature, especially during Aiken's cooler winter months when incoming water temperatures drop.
Wire Gauge Requirements
Each of those dedicated circuits requires appropriately sized wire. For a 40-amp circuit, the NEC requires a minimum of 8 AWG copper conductors. For 50-amp circuits, you need 6 AWG copper. The wire must be rated for the amperage and the distance of the run from your panel to the water heater location. Longer runs may require stepping up to a larger gauge to account for voltage drop, which reduces efficiency and can cause the unit to malfunction.
In many Aiken homes, the water heater is located in a garage, utility closet, or crawl space that may be some distance from the electrical panel. If the run exceeds 50 feet, your electrician will calculate the voltage drop and may recommend upgrading from 8 AWG to 6 AWG even on a 40-amp circuit. Using undersized wire creates a fire hazard and will not pass inspection.
Does Your Panel Have Enough Capacity?
Here is where the real cost consideration comes in. Adding three or four 40-amp circuits to your electrical panel requires a significant amount of available amperage. A 24-kilowatt tankless unit on three 40-amp circuits adds 120 amps of potential load to your panel. If your Aiken home has a 200-amp main panel, those three circuits alone consume 60 percent of your total panel capacity. If your home still has a 100-amp or 150-amp panel, which is common in homes built before 2000, there simply may not be enough room.
Many homeowners discover that installing a tankless water heater requires a panel upgrade as part of the project. Upgrading from a 100-amp panel to a 200-amp panel is a substantial job that involves coordination with the utility company, a new meter base, a new panel, and new main feeder wires. It is a worthwhile upgrade that benefits your entire home, but it adds to the project cost and timeline.
Even if your panel has 200 amps, it may not have enough physical space for three or four new double-pole breakers. Older panels may be fully loaded with existing circuits. In these cases, a subpanel or panel replacement may be necessary to accommodate the new circuits.
Cost of Electrical Upgrades for Tankless Installation
The electrical work for a tankless water heater installation typically costs more than the unit itself. Here is what Aiken homeowners can expect:
- Running new circuits only (panel has capacity) — $800 to $1,500 for two to four dedicated circuits including wire, breakers, and labor
- Panel upgrade required (100-amp to 200-amp) — $2,000 to $4,000 for the panel upgrade, plus the circuit costs above
- Subpanel addition — $1,200 to $2,500 if a subpanel is the most practical solution
- Permit and inspection — Aiken County requires a permit for this type of electrical work, typically $75 to $150
When you add the cost of the tankless unit itself, which ranges from $500 to $1,200 for a whole-house electric model, plus plumbing modifications, the total project cost frequently lands between $2,500 and $6,000. Homeowners who were expecting to simply swap out their old tank heater are often surprised by the scope of electrical work involved.
Gas vs Electric Tankless: The Electrical Perspective
If the electrical requirements of an electric tankless unit seem daunting, there is an alternative worth considering. A gas-powered tankless water heater (natural gas or propane) heats water using a burner rather than electrical elements. The electrical requirements for a gas tankless unit are minimal: a single standard 120-volt, 15-amp outlet for the electronic controls and ignition system. This is a fraction of the electrical demand of an electric model.
However, gas tankless units have their own requirements. They need a gas line sized for the unit's BTU rating, proper venting (either power vent or direct vent through an exterior wall), and adequate combustion air. If your Aiken home does not already have a gas line to the water heater location, running one adds cost. Gas units also cost more upfront, typically $1,000 to $2,000 for the unit alone. But the dramatically lower electrical requirements mean you almost certainly will not need a panel upgrade.
For Aiken homes with natural gas service and an existing gas line near the water heater location, a gas tankless unit is often the simpler and less expensive path. For all-electric homes or locations where gas is not practical, an electric tankless unit is the way to go, but budget for the electrical infrastructure.
What to Do Before Buying a Tankless Water Heater
Before you purchase a tankless water heater or commit to a plumber's installation quote, have an electrician evaluate your panel and wiring. This assessment will tell you exactly what electrical work is needed, whether your panel can handle the additional load, and what the electrical portion of the project will cost. Without this information, you are making a major purchase decision without knowing the full price.
At Unity Power and Light, we perform these evaluations for Aiken homeowners regularly. We will inspect your panel capacity, measure your existing loads, calculate wire run distances, and give you a clear picture of what the electrical side of your tankless installation will require and cost. If a panel upgrade makes sense, we will explain why and provide a complete quote that covers everything from permit to final inspection.