The short answer depends on the fuel. A gas tankless water heater draws only a few amps on a standard 120-volt outlet. A whole-house electric tankless unit draws between 75 and 150 amps at 240 volts, which is more than many homes can spare. That difference decides whether your install is a simple swap or a job that starts at the electrical panel.
If you are weighing a tankless water heater installation in Sacramento, this is the first number to check.
How to Calculate the Amps
Electric tankless heaters are rated in kilowatts. To find the current they draw, divide the watts by the voltage.
Amps = kilowatts × 1,000 ÷ volts
An 18 kW unit on a 240-volt circuit draws 18,000 ÷ 240 = 75 amps. That is roughly what two electric ranges draw with every burner and the oven on at once, and the heater pulls it every time someone opens a hot tap.
Typical Amp Draw by Unit Size
| Unit size | Amps at 240 V | What it usually serves |
|---|---|---|
| 3.5 to 7 kW | 15 to 29 A | One sink, point-of-use |
| 9 to 13 kW | 38 to 54 A | One shower in a warm climate |
| 18 kW | 75 A | One to two fixtures at a time |
| 24 kW | 100 A | Two showers at a time |
| 27 kW | 113 A | Two to three fixtures |
| 36 kW | 150 A | Whole house, colder inlet water |
Larger units split the load across two, three, or four double-pole breakers. The manufacturer’s installation manual sets the exact breaker and wire size for each model, and that manual is what the inspector checks.
Gas Tankless Units Use Very Little Electricity
A gas tankless heater burns natural gas to heat the water. Electricity only runs the controls, the igniter, and the exhaust fan. Most models plug into a standard 120-volt outlet and draw a few amps. Some add a small freeze-protection heater that runs in cold weather.
The gas side is the hard part. A whole-house gas tankless unit needs far more gas than a tank heater, so the existing gas line is often too small. Upsizing the line, adding a new vent, and pulling a permit are part of most gas tankless installs. Our gas line team handles that work under the same permit.
Can Your Electrical Panel Handle It?
Many older Sacramento homes still run on a 100-amp panel. A 27 kW electric tankless unit alone would ask for more than the whole house is rated to carry. In practice, a whole-house electric tankless heater usually needs a 200-amp service, and sometimes a utility upgrade from SMUD.
Before anyone recommends an electric unit, a licensed electrician should run a load calculation. That calculation adds up everything the house already uses: the air conditioner, the range, the dryer, an EV charger, and any heat pump. If the numbers do not leave room, the choice is between a panel upgrade, a smaller point-of-use unit, a gas tankless heater, or a heat pump water heater.
We keep a licensed electrician on staff, so the load calculation and any panel work are done by our own team, not a subcontractor.
Electric, Gas, or Heat Pump: A Quick Comparison
- Gas tankless: low electrical draw, high gas demand, needs venting. Best when gas is already at the heater location.
- Electric tankless: no venting, very high amp draw. Best for small homes, point-of-use, or houses that already have spare panel capacity.
- Heat pump water heater: stores hot water like a tank, draws far less current than electric tankless, and is the most efficient electric option. Compare the options on our water heater services page.
Tankless Water Heater Amps: Common Questions
Can I run an electric tankless water heater on a 100-amp panel?
No, not for a whole-house unit in most cases. A 100-amp panel rarely has 75 to 150 amps to spare once the rest of the house is counted. A small point-of-use unit for one sink can work, but only after a load calculation confirms it.
How many breakers does an electric tankless heater need?
It depends on the size. A unit under about 13 kW usually needs one double-pole breaker. An 18 kW unit usually needs two, a 27 kW unit three, and a 36 kW unit four. The installation manual for your model sets the exact breaker and wire gauge.
Does a gas tankless water heater need its own circuit?
No, it usually does not. Most gas units plug into a standard 120-volt outlet near the heater. The outlet must be within reach of the power cord and meet code for its location.
Do I need a permit to install a tankless water heater in Sacramento?
Yes, you do. Water heater installs require a permit and an inspection. If electrical or gas work is part of the job, it goes on the same permit, and we file it under CSLB #1038276.
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Not Sure What Your Home Can Support?
Send us a photo of your electrical panel label and your current water heater, and we will tell you which options fit before anyone opens a wall. Learn more about our tankless water heater installation.
